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jluckey(at)pacbell.net
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 Posted: Wed Dec 04, 2013 9:09 pm Post subject: Unprotected Feeder in Z Drawings |
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Bob,
I have been reviewing some of the Z drawings in the back of "The Aeroelectric Connection" and I have a question. (specifically Z-11, Z-12, & Z-14)
I notice that the 6 awg wire which connects the load side of the Battery Contactor to the Main Power Distribution bus is not fused. That seems like an un-protected feeder and gives me a little heart burn.
I think of the Main Power Distribution bus as the bus bar which runs across the back of the breakers in my distribution panel which lives in my instrument panel. With the Battery Contactor on the firewall, the run from it to the distribution panel penetrates the firewall then snakes its way to the back of my panel. That #6 wire will be between 6 & 8 feet in length.
What happens if that wire gets into trouble along its route. Without a fuse it will get very hot and bad things will happen.
I'm curious about the criteria used in this design. Perhaps I'm missing something?
TIA,
-Jeff
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Thu Dec 05, 2013 7:55 am Post subject: Unprotected Feeder in Z Drawings |
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At 11:00 PM 12/4/2013, you wrote:
Bob,
I have been reviewing some of the Z drawings in the back of "The
Aeroelectric Connection" and I have a question. (specifically Z-11,
Z-12, & Z-14)
I notice that the 6 awg wire which connects the load side of the
Battery Contactor to the Main Power Distribution bus is not
fused. That seems like an un-protected feeder and gives me a little
heart burn.
I think of the Main Power Distribution bus as the bus bar which runs
across the back of the breakers in my distribution panel which lives
in my instrument panel. With the Battery Contactor on the firewall,
the run from it to the distribution panel penetrates the firewall
then snakes its way to the back of my panel. That #6 wire will be
between 6 & 8 feet in length.
What happens if that wire gets into trouble along its route. Without
a fuse it will get very hot and bad things will happen.
I'm curious about the criteria used in this design. Perhaps I'm
missing something?
TIA,
-Jeff
Okay,
Get out your toolbox and take a position to contemplate this 'risky'
piece of wire. What process and tools are needed to 'get this wire
into trouble'? Yes, it's attached to a battery with potential for
spectacular fault currents, but so too is your propeller thrashing
around in the breeze with a potential for serious bodily harm.
It's easy to get bogged down worrying about things that have low to
exceedingly small probability of happening. This is a fundamental
component of Failure Modes Effects Analysis. The artfully crafted
FMEA not only considers "what happens if . . .?" you're well advised
to consider HOW that condition became a thing to consider in the
first place. The goal is to decide which has more value: (1)
protecting against a condition or (2) reducing probability of that
condition to an acceptably low value.
In the case of your fat-wire, which design goal offers the lowest
level of risk and greatest boost of system reliability? (1) protect
the wire loaded to some gawd-awful fault or (2) reduce probability of
such an event to levels that says your worry-capital is better
invested elsewhere? This thought process convinces us that building
a safety cage around the propeller is not a useful/necessary
expenditure of weight/cost/performance budget.
There are exposed conductors that run across the back of most circuit
breaker panels. These bus bars are legacy features of all manner of
vehicle not the least of which are airplanes. Is there value in
expending worry-capital on risk for faulting a bus bar? You can
answer this question with pretty simple observation and
contemplation. With a box full of tools at your disposal, what parts
of the airplane do you have to hammer, pry or saw in order to get
that bus bar . . . or your fat-wire into trouble?
Once those actions are discovered and evaluated, what is the
likelihood that such an event is going to befall the potential victim
over the lifetime of your airplane? It's fairly predicable that your
study will produce some combination of discoveries that fall in to
two categories: (1) there are no features of structure or installed
hardware likely to dislodge and attack the potential victim; (2)
Oops! Some feature of installation of the wire or surrounds has not
been installed with attention to good practices . . . and you're
going to fix it.
This same analysis (and incorporation of lessons-learned) produced
the following excerpt from FAR23 for TC aircraft:
Sec. 23.1357 Circuit protective devices.
(a) Protective devices, such as fuses or circuit breakers, must be
installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting
only; and
(2) Circuits in which no hazard is presented by their omission.
<continued>
The controlling idea here is 23.1357(a)(2) where you're going to
manage the installation of this 6AWG wire and its surrounds such that
"no hazard is presented" by omission of a fuse or breaker.
Bob . . .
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jluckey(at)pacbell.net
Guest
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| Posted: Thu Dec 05, 2013 8:21 am Post subject: Unprotected Feeder in Z Drawings |
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Thank you for the explanation. I get it - the assumption is: very low probability of the wire getting into trouble assuming that it's well-installed w/ intelligence and craftsmanship.
But staying with the original theme, is there any down side to putting a big current limiter (ANL?) in that lead at its origin?
-Jeff
PS - I'm also thinking about ways to protect that buss bar 
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Thursday, December 5, 2013 7:54 AM
Subject: Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 11:00 PM 12/4/2013, you wrote:
Bob,
I have been reviewing some of the Z drawings in the back of "The Aeroelectric Connection" and I have a question. (specifically Z-11, Z-12, & Z-14)
I notice that the 6 awg wire which connects the load side of the Battery Contactor to the Main Power Distribution bus is not fused. That seems like an un-protected feeder and gives me a little heart burn.
I think of the Main Power Distribution bus as the bus bar which runs across the back of the breakers in my distribution panel which lives in my instrument panel. With the Battery Contactor on the firewall, the run from it to the distribution panel penetrates the firewall then snakes its way to the back of my panel. That #6 wire will be between 6 & 8 feet in length.
What happens if that wire gets into trouble along its route. Without a fuse it will get very hot and bad things will happen.
I'm curious about the criteria used in this design. Perhaps I'm missing something?
TIA,
-Jeff
Okay,
Get out your toolbox and take a position to contemplate this 'risky' piece of wire. What process and tools are needed to 'get this wire into trouble'? Yes, it's attached to a battery with potential for spectacular fault currents, but so too is your propeller thrashing around in the breeze with a potential for serious bodily harm.
It's easy to get bogged down worrying about things that have low to exceedingly small probability of happening. This is a fundamental component of Failure Modes Effects Analysis. The artfully crafted FMEA not only considers "what happens if . . .?" you're well advised to consider HOW that condition became a thing to consider in the first place. The goal is to decide which has more value: (1) protecting against a condition or (2) reducing probability of that condition to an acceptably low value.
In the case of your fat-wire, which design goal offers the lowest level of risk and greatest boost of system reliability? (1) protect the wire loaded to some gawd-awful fault or (2) reduce probability of such an event to levels that says your worry-capital is better invested elsewhere? This thought process convinces us that building a safety cage around the propeller is not a useful/necessary expenditure of weight/cost/performance budget.
There are exposed conductors that run across the back of most circuit breaker panels. These bus bars are legacy features of all manner of vehicle not the least of which are airplanes. Is there value in expending worry-capital on risk for faulting a bus bar? You can answer this question with pretty simple observation and contemplation. With a box full of tools at your disposal, what parts of the airplane do you have to hammer, pry or saw in order to get that bus bar . . . or your fat-wire into trouble?
Once those actions are discovered and evaluated, what is the likelihood that such an event is going to befall the potential victim over the lifetime of your airplane? It's fairly predicable that your study will produce some combination of discoveries that fall in to two categories: (1) there are no features of structure or installed hardware likely to dislodge and attack the potential victim; (2) Oops! Some feature of installation of the wire or surrounds has not been installed with attention to good practices . . . and you're going to fix it.
This same analysis (and incorporation of lessons-learned) produced the following excerpt from FAR23 for TC aircraft:
Sec. 23.1357 Circuit protective devices.
(a) Protective devices, such as fuses or circuit breakers, must be
installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.
<continued>
The controlling idea here is 23.1357(a)(2) where you're going to manage the installation of this 6AWG wire and its surrounds such that "no hazard is presentedution link below to find out more ronics.com/contribution" target="_blank">http://www.matronics.com/contribst -> http://www.matronics.com/Navigator?AeroElectric-List
_ref="http://forums.matronics.com/" target="_blank">http://forums.matron===================
[quote][b]
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klehman(at)albedo.net
Guest
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| Posted: Thu Dec 05, 2013 8:42 am Post subject: Unprotected Feeder in Z Drawings |
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|
Additional voltage drop and connections that could fail.
What size ANL would you propose?
A 200 amp ANL would start most engines but would it increase safety if
it limited a short to only 2 or 300 amps of arcing for only say 10 seconds?
A 200 amp arc will almost certainly melt airframe material which will
increase the arc length and self extinguish within that time frame anyway.
Ken
On 05/12/2013 11:20 AM, Jeff Luckey wrote:
| Quote: | Thank you for the explanation. I get it - the assumption is: very low
probability of the wire getting into trouble assuming that it's
well-installed w/ intelligence and craftsmanship.
But staying with the original theme, is there any down side to putting a
big current limiter (ANL?) in that lead at its origin?
-Jeff
PS - I'm also thinking about ways to protect that buss bar
------------------------------------------------------------------------
*From:* "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
*To:* aeroelectric-list(at)matronics.com
*Sent:* Thursday, December 5, 2013 7:54 AM
*Subject:* Re: Unprotected Feeder in Z Drawings
<nuckolls.bob(at)aeroelectric.com <mailto:nuckolls.bob(at)aeroelectric.com>>
At 11:00 PM 12/4/2013, you wrote:
Bob,
I have been reviewing some of the Z drawings in the back of "The
Aeroelectric Connection" and I have a question. (specifically Z-11,
Z-12, & Z-14)
I notice that the 6 awg wire which connects the load side of the Battery
Contactor to the Main Power Distribution bus is not fused. That seems
like an un-protected feeder and gives me a little heart burn.
I think of the Main Power Distribution bus as the bus bar which runs
across the back of the breakers in my distribution panel which lives in
my instrument panel. With the Battery Contactor on the firewall, the
run from it to the distribution panel penetrates the firewall then
snakes its way to the back of my panel. That #6 wire will be between 6
& 8 feet in length.
What happens if that wire gets into trouble along its route. Without a
fuse it will get very hot and bad things will happen.
I'm curious about the criteria used in this design. Perhaps I'm missing
something?
TIA,
-Jeff
Okay,
Get out your toolbox and take a position to contemplate this 'risky'
piece of wire. What process and tools are needed to 'get this wire into
trouble'? Yes, it's attached to a battery with potential for spectacular
fault currents, but so too is your propeller thrashing around in the
breeze with a potential for serious bodily harm.
It's easy to get bogged down worrying about things that have low to
exceedingly small probability of happening. This is a fundamental
component of Failure Modes Effects Analysis. The artfully crafted FMEA
not only considers "what happens if . . .?" you're well advised to
consider HOW that condition became a thing to consider in the first
place. The goal is to decide which has more value: (1) protecting
against a condition or (2) reducing probability of that condition to an
acceptably low value.
In the case of your fat-wire, which design goal offers the lowest level
of risk and greatest boost of system reliability? (1) protect the wire
loaded to some gawd-awful fault or (2) reduce probability of such an
event to levels that says your worry-capital is better invested
elsewhere? This thought process convinces us that building a safety
cage around the propeller is not a useful/necessary expenditure of
weight/cost/performance budget.
There are exposed conductors that run across the back of most circuit
breaker panels. These bus bars are legacy features of all manner of
vehicle not the least of which are airplanes. Is there value in
expending worry-capital on risk for faulting a bus bar? You can answer
this question with pretty simple observation and contemplation. With a
box full of tools at your disposal, what parts of the airplane do you
have to hammer, pry or saw in order to get that bus bar . . . or your
fat-wire into trouble?
Once those actions are discovered and evaluated, what is the likelihood
that such an event is going to befall the potential victim over the
lifetime of your airplane? It's fairly predicable that your study will
produce some combination of discoveries that fall in to two categories:
(1) there are no features of structure or installed hardware likely to
dislodge and attack the potential victim; (2) Oops! Some feature of
installation of the wire or surrounds has not been installed with
attention to good practices . . . and you're going to fix it.
This same analysis (and incorporation of lessons-learned) produced the
following excerpt from FAR23 for TC aircraft:
Sec. 23.1357 Circuit protective devices.
(a) Protective devices, such as fuses or circuit breakers, must be
installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.
<continued>
The controlling idea here is 23.1357(a)(2) where you're going to manage
the installation of this 6AWG wire and its surrounds such that "no
hazard is presentedution link below to find out more
ronics.com/contribution"
target="_blank">http://www.matronics.com/contribst ->
http://www.matronics.com/Navigator?AeroElectric-List
_ref="http://forums.matronics.com/"
target="_blank">http://forums.matron===================
|
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http://www.matronics.com/Navigator?AeroElectric-List |
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jluckey(at)pacbell.net
Guest
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| Posted: Thu Dec 05, 2013 9:04 am Post subject: Unprotected Feeder in Z Drawings |
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|
Ken,
In the circuit that I'm thinking about the ANL would not be in the starter circuit - only in the feed to the distribution panel and maybe in the 60-80 amp range.
I think voltage drop will be very minimal. Additional failure points, sure, but if we are assuming quality components & workmanship that risk is also minimal.
-Jeff
From: Ken <klehman(at)albedo.net>
To: aeroelectric-list(at)matronics.com
Sent: Thursday, December 5, 2013 8:42 AM
Subject: Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: Ken <klehman(at)albedo.net (klehman(at)albedo.net)>
Additional voltage drop and connections that could fail.
What size ANL would you propose?
A 200 amp ANL would start most engines but would it increase safety if
it limited a short to only 2 or 300 amps of arcing for only say 10 seconds?
A 200 amp arc will almost certainly melt airframe material which will
increase the arc length and self extinguish within that time frame anyway.
Ken
On 05/12/2013 11:20 AM, Jeff Luckey wrote:
| Quote: | Thank you for the explanation. I get it - the assumption is: very low
probability of the wire getting into trouble assuming that it's
well-installed w/ intelligence and craftsmanship.
But staying with the original theme, is there any down side to putting a
big current limiter (ANL?) in that lead at its origin?
-Jeff
PS - I'm also thinking about ways to protect that buss bar
------------------------------------------------------------------------
*From:* "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
*To:* aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
*Sent:* Thursday, December 5, 2013 7:54 AM
*Subject:* Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com) <mailto:nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>>
At 11:00 PM 12/4/2013, you wrote:
Bob,
I have been reviewing some of the Z drawings in the back of "The
Aeroelectric Connection" and I have a question. (specifically Z-11,
Z-12, & Z-14)
I notice that the 6 awg wire which connects the load side of the Battery
Contactor to the Main Power Distribution bus is not fused. That seems
like an un-protected feeder and gives me a little heart burn.
I think of the Main Power Distribution bus as the bus bar which runs
across the back of the breakers in my distribution panel which lives in
my instrument panel. With the Battery Contactor on the firewall, the
run from it to the distribution panel penetrates the firewall then
snakes its way to the back of my panel. That #6 wire will be between 6
& 8 feet in length.
What happens if that wire gets into trouble along its route. Without a
fuse it will get very hot and bad things will happen.
I'm curious about the criteria used in this design. Perhaps I'm missing
something?
TIA,
-Jeff
Okay,
Get out your toolbox and take a position to contemplate this 'risky'
piece of wire. What process and tools are needed to 'get this wire into
trouble'? Yes, it's attached to a battery with potential for spectacular
fault currents, but so too is your propeller thrashing around in the
breeze with a potential for serious bodily harm.
It's easy to get bogged down worrying about things that have low to
exceedingly small probability of happening. This is a fundamental
component of Failure Modes Effects Analysis. The artfully crafted FMEA
not only considers "what happens if . . .?" you're well advised to
consider HOW that condition became a thing to consider in the first
place. The goal is to decide which has more value: (1) protecting
against a condition or (2) reducing probability of that condition to an
acceptably low value.
In the case of your fat-wire, which design goal offers the lowest level
of risk and greatest boost of system reliability? (1) protect the wire
loaded to some gawd-awful fault or (2) reduce probability of such an
event to levels that says your worry-capital is better invested
elsewhere? This thought process convinces us that building a safety
cage around the propeller is not a useful/necessary expenditure of
weight/cost/performance budget.
There are exposed conductors that run across the back of most circuit
breaker panels. These bus bars are legacy features of all manner of
vehicle not the least of which are airplanes. Is there value in
expending worry-capital on risk for faulting a bus bar? You can answer
this question with pretty simple observation and contemplation. With a
box full of tools at your disposal, what parts of the airplane do you
have to hammer, pry or saw in order to get that bus bar . . . or your
fat-wire into trouble?
Once those actions are discovered and evaluated, what is the likelihood
that such an event is going to befall the potential victim over the
lifetime of your airplane? It's fairly predicable that your study will
produce some combination of discoveries that fall in to two categories:
(1) there are no features of structure or installed hardware likely to
dislodge and attack the potential victim; (2) Oops! Some feature of
installation of the wire or surrounds has not been installed with
attention to good practices . . . and you're going to fix it.
This same analysis (and incorporation of lessons-learned) produced the
following excerpt from FAR23 for TC aircraft:
Sec. 23.1357 Circuit protective devices.
(a) Protective devices, such as fuses or circuit breakers, must be
installed in all electrical circuits other than--
(1) Main circuits of starter motors used during starting only; and
(2) Circuits in which no hazard is presented by their omission.
<continued>
The controlling idea here is 23.1357(a)(2) where you're going to manage
the installation of this 6AWG wire and its surrounds such that "no
hazard is presentedution link below to find out more
ronics.com/contribution"
target="_blank">http://www.matronics.com/contribst ->
http://www.matronics.com/Navigator?AeroElectric-List
_ref="http://forums.matronics.com/"
target="_blank">http://forums.matron==============p://www.matronics.com/contribution" target="_blank">http://www.matronics.nbsp; -Matt Dralle, List Atric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectrip; --> http:========================
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[quote][b]
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klehman(at)albedo.net
Guest
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| Posted: Thu Dec 05, 2013 9:40 am Post subject: Unprotected Feeder in Z Drawings |
|
|
Jeff
In that case if you decide to do it I'd suggest that something like a
maxi fuse would be more appropriate than a very slow acting ANL. I'd
still lean towards no protection but you are obviously more familiar
with your wire routing. I'd make sure that it isn't going to present a
major problem though if you get a nuisance trip after takeoff.
Ken
On 05/12/2013 12:03 PM, Jeff Luckey wrote:
| Quote: | Ken,
In the circuit that I'm thinking about the ANL would not be in the
starter circuit - only in the feed to the distribution panel and maybe
in the 60-80 amp range.
I think voltage drop will be very minimal. Additional failure points,
sure, but if we are assuming quality components & workmanship that risk
is also minimal.
-Jeff
------------------------------------------------------------------------
*From:* Ken <klehman(at)albedo.net>
*To:* aeroelectric-list(at)matronics.com
*Sent:* Thursday, December 5, 2013 8:42 AM
*Subject:* Re: Unprotected Feeder in Z Drawings
<mailto:klehman(at)albedo.net>>
Additional voltage drop and connections that could fail.
What size ANL would you propose?
A 200 amp ANL would start most engines but would it increase safety if
it limited a short to only 2 or 300 amps of arcing for only say 10 seconds?
A 200 amp arc will almost certainly melt airframe material which will
increase the arc length and self extinguish within that time frame anyway.
Ken
On 05/12/2013 11:20 AM, Jeff Luckey wrote:
> Thank you for the explanation. I get it - the assumption is: very low
> probability of the wire getting into trouble assuming that it's
> well-installed w/ intelligence and craftsmanship.
>
> But staying with the original theme, is there any down side to putting a
> big current limiter (ANL?) in that lead at its origin?
>
> -Jeff
>
> PS - I'm also thinking about ways to protect that buss bar
>
> ------------------------------------------------------------------------
> *From:* "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com
<mailto:nuckolls.bob(at)aeroelectric.com>>
> *To:* aeroelectric-list(at)matronics.com
<mailto:aeroelectric-list(at)matronics.com>
> *Sent:* Thursday, December 5, 2013 7:54 AM
> *Subject:* Re: Unprotected Feeder in Z Drawings
>
>
> <nuckolls.bob(at)aeroelectric.com <mailto:nuckolls.bob(at)aeroelectric.com>
<mailto:nuckolls.bob(at)aeroelectric.com
<mailto:nuckolls.bob(at)aeroelectric.com>>>
>
> At 11:00 PM 12/4/2013, you wrote:
> Bob,
>
> I have been reviewing some of the Z drawings in the back of "The
> Aeroelectric Connection" and I have a question. (specifically Z-11,
> Z-12, & Z-14)
>
> I notice that the 6 awg wire which connects the load side of the Battery
> Contactor to the Main Power Distribution bus is not fused. That seems
> like an un-protected feeder and gives me a little heart burn.
>
> I think of the Main Power Distribution bus as the bus bar which runs
> across the back of the breakers in my distribution panel which lives in
> my instrument panel. With the Battery Contactor on the firewall, the
> run from it to the distribution panel penetrates the firewall then
> snakes its way to the back of my panel. That #6 wire will be between 6
> & 8 feet in length.
>
> What happens if that wire gets into trouble along its route. Without a
> fuse it will get very hot and bad things will happen.
>
> I'm curious about the criteria used in this design. Perhaps I'm missing
> something?
>
> TIA,
>
> -Jeff
>
> Okay,
>
> Get out your toolbox and take a position to contemplate this 'risky'
> piece of wire. What process and tools are needed to 'get this wire into
> trouble'? Yes, it's attached to a battery with potential for spectacular
> fault currents, but so too is your propeller thrashing around in the
> breeze with a potential for serious bodily harm.
>
> It's easy to get bogged down worrying about things that have low to
> exceedingly small probability of happening. This is a fundamental
> component of Failure Modes Effects Analysis. The artfully crafted FMEA
> not only considers "what happens if . . .?" you're well advised to
> consider HOW that condition became a thing to consider in the first
> place. The goal is to decide which has more value: (1) protecting
> against a condition or (2) reducing probability of that condition to an
> acceptably low value.
>
> In the case of your fat-wire, which design goal offers the lowest level
> of risk and greatest boost of system reliability? (1) protect the wire
> loaded to some gawd-awful fault or (2) reduce probability of such an
> event to levels that says your worry-capital is better invested
> elsewhere? This thought process convinces us that building a safety
> cage around the propeller is not a useful/necessary expenditure of
> weight/cost/performance budget.
>
> There are exposed conductors that run across the back of most circuit
> breaker panels. These bus bars are legacy features of all manner of
> vehicle not the least of which are airplanes. Is there value in
> expending worry-capital on risk for faulting a bus bar? You can answer
> this question with pretty simple observation and contemplation. With a
> box full of tools at your disposal, what parts of the airplane do you
> have to hammer, pry or saw in order to get that bus bar . . . or your
> fat-wire into trouble?
>
> Once those actions are discovered and evaluated, what is the likelihood
> that such an event is going to befall the potential victim over the
> lifetime of your airplane? It's fairly predicable that your study will
> produce some combination of discoveries that fall in to two categories:
> (1) there are no features of structure or installed hardware likely to
> dislodge and attack the potential victim; (2) Oops! Some feature of
> installation of the wire or surrounds has not been installed with
> attention to good practices . . . and you're going to fix it.
>
> This same analysis (and incorporation of lessons-learned) produced the
> following excerpt from FAR23 for TC aircraft:
>
>
> Sec. 23.1357 Circuit protective devices.
>
> (a) Protective devices, such as fuses or circuit breakers, must be
> installed in all electrical circuits other than--
>
> (1) Main circuits of starter motors used during starting
only; and
> (2) Circuits in which no hazard is presented by their omission.
>
> <continued>
>
> The controlling idea here is 23.1357(a)(2) where you're going to manage
> the installation of this 6AWG wire and its surrounds such that "no
> hazard is presentedution link below to find out more
> ronics.com/contribution"
> target="_blank">http://www.matronics.com/contribst ->
> http://www.matronics.com/Navigator?AeroElectric-List
> _ref="http://forums.matronics.com/"
>
target="_blank">http://forums.matron==============p://www.matronics.com/contribution"
target="_blank">http://www.matronics.nbsp; -Matt Dralle,
List Atric-List"
target="_blank">http://www.matronics.com/Navigator?AeroElectrip; -->
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jluckey(at)pacbell.net
Guest
|
| Posted: Thu Dec 05, 2013 10:17 am Post subject: Unprotected Feeder in Z Drawings |
|
|
Ken,
I think you put your finger on it - I'm interested in analyzing the potential for events which are non-catastrophic & transient in nature that might cause the fuse to pop un-necessarily (nuisance trip).
I think that's a pretty small universe and at the moment I can't think of an example of such an event - perhaps that's because there are none. I'm hoping the brain trust on this list can think of such an event that I may be overlooking.
-Jeff
From: Ken <klehman(at)albedo.net>
To: aeroelectric-list(at)matronics.com
Sent: Thursday, December 5, 2013 9:39 AM
Subject: Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: Ken <klehman(at)albedo.net (klehman(at)albedo.net)>
Jeff
In that case if you decide to do it I'd suggest that something like a
maxi fuse would be more appropriate than a very slow acting ANL. I'd
still lean towards no protection but you are obviously more familiar
with your wire routing. I'd make sure that it isn't going to present a
major problem though if you get a nuisance trip after takeoff.
Ken
On 05/12/2013 12:03 PM, Jeff Luckey wrote:
| Quote: | Ken,
In the circuit that I'm thinking about the ANL would not be in the
starter circuit - only in the feed to the distribution panel and maybe
in the 60-80 amp range.
I think voltage drop will be very minimal. Additional failure points,
sure, but if we are assuming quality components & workmanship that risk
is also minimal.
-Jeff
------------------------------------------------------------------------
*From:* Ken <klehman(at)albedo.net (klehman(at)albedo.net)>
*To:* aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
*Sent:* Thursday, December 5, 2013 8:42 AM
*Subject:* Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: Ken <klehman(at)albedo.net (klehman(at)albedo.net)
<mailto:klehman(at)albedo.net (klehman(at)albedo.net)>>
Additional voltage drop and connections that could fail.
What size ANL would you propose?
A 200 amp ANL would start most engines but would it increase safety if
it limited a short to only 2 or 300 amps of arcing for only say 10 seconds?
A 200 amp arc will almost certainly melt airframe material which will
increase the arc length and self extinguish within that time frame anyway.
Ken
On 05/12/2013 11:20 AM, Jeff Luckey wrote:
> Thank you for the explanation. I get it - the assumption is: very low
> probability of the wire getting into trouble assuming that it's
> well-installed w/ intelligence and craftsmanship.
>
> But staying with the original theme, is there any down side to putting a
> big current limiter (ANL?) in that lead at its origin?
>
> -Jeff
>
> PS - I'm also thinking about ways to protect that buss bar
>
> ------------------------------------------------------------------------
> *From:* "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)
<mailto:nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>>
> *To:* aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
<mailto:aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)>
> *Sent:* Thursday, December 5, 2013 7:54 AM
> *Subject:* Re: AeroElectric-List: Unprotected Feeder in Z Drawings
>
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com) <mailto:nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
<mailto:nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)
<mailto:nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>>>
>
> At 11:00 PM 12/4/2013, you wrote:
> Bob,
>
> I have been reviewing some of the Z drawings in the back of "The
> Aeroelectric Connection" and I have a question. (specifically Z-11,
> Z-12, & Z-14)
>
> I notice that the 6 awg wire which connects the load side of the Battery
> Contactor to the Main Power Distribution bus is not fused. That seems
> like an un-protected feeder and gives me a little heart burn.
>
> I think of the Main Power Distribution bus as the bus bar which runs
> across the back of the breakers in my distribution panel which lives in
> my instrument panel. With the Battery Contactor on the firewall, the
> run from it to the distribution panel penetrates the firewall then
> snakes its way to the back of my panel. That #6 wire will be between 6
> & 8 feet in length.
>
> What happens if that wire gets into trouble along its route. Without a
> fuse it will get very hot and bad things will happen.
>
> I'm curious about the criteria used in this design. Perhaps I'm missing
> something?
>
> TIA,
>
> -Jeff
>
> Okay,
>
> Get out your toolbox and take a position to contemplate this 'risky'
> piece of wire. What process and tools are needed to 'get this wire into
> trouble'? Yes, it's attached to a battery with potential for spectacular
> fault currents, but so too is your propeller thrashing around in the
> breeze with a potential for serious bodily harm.
>
> It's easy to get bogged down worrying about things that have low to
> exceedingly small probability of happening. This is a fundamental
> component of Failure Modes Effects Analysis. The artfully crafted FMEA
> not only considers "what happens if . . .?" you're well advised to
> consider HOW that condition became a thing to consider in the first
> place. The goal is to decide which has more value: (1) protecting
> against a condition or (2) reducing probability of that condition to an
> acceptably low value.
>
> In the case of your fat-wire, which design goal offers the lowest level
> of risk and greatest boost of system reliability? (1) protect the wire
> loaded to some gawd-awful fault or (2) reduce probability of such an
> event to levels that says your worry-capital is better invested
> elsewhere? This thought process convinces us that building a safety
> cage around the propeller is not a useful/necessary expenditure of
> weight/cost/performance budget.
>
> There are exposed conductors that run across the back of most circuit
> breaker panels. These bus bars are legacy features of all manner of
> vehicle not the least of which are airplanes. Is there value in
> expending worry-capital on risk for faulting a bus bar? You can answer
> this question with pretty simple observation and contemplation. With a
> box full of tools at your disposal, what parts of the airplane do you
> have to hammer, pry or saw in order to get that bus bar . . . or your
> fat-wire into trouble?
>
> Once those actions are discovered and evaluated, what is the likelihood
> that such an event is going to befall the potential victim over the
> lifetime of your airplane? It's fairly predicable that your study will
> produce some combination of discoveries that fall in to two categories:
> (1) there are no features of structure or installed hardware likely to
> dislodge and attack the potential victim; (2) Oops! Some feature of
> installation of the wire or surrounds has not been installed with
> attention to good practices . . . and you're going to fix it.
>
> This same analysis (and incorporation of lessons-learned) produced the
> following excerpt from FAR23 for TC aircraft:
>
>
> Sec. 23.1357 Circuit protective devices.
>
> (a) Protective devices, such as fuses or circuit breakers, must be
> installed in all electrical circuits other than--
>
> (1) Main circuits of starter motors used during starting
only; and
> (2) Circuits in which no hazard is presented by their omission.
>
> <continued>
>
> The controlling idea here is 23.1357(a)(2) where you're going to manage
> the installation of this 6AWG wire and its surrounds such that "no
> hazard is presentedution link below to find out more
> ronics.com/contribution"
> target="_blank">http://www.matronics.com/contribst ->
> http://www.matronics.com/Navigator?AeroElectric-List
> _ref="http://forums.matronics.com/"
>
target="_blank">http://forums.matron==============p://www.matronics.com/contribution"
target="_blank">http://www.matronics.nbsp; -Matt Dralle,
List Atric-List"
target="_blank">http://www.matronics.com/Navigator?AeroElectrip; -->
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nuckolls.bob(at)aeroelect
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Fri Dec 06, 2013 5:19 am Post subject: Unprotected Feeder in Z Drawings |
|
|
At 12:16 PM 12/5/2013, you wrote:
| Quote: | Ken,
I think you put your finger on it - I'm interested in analyzing the
potential for events which are non-catastrophic & transient in
nature that might cause the fuse to pop un-necessarily (nuisance trip).
I think that's a pretty small universe and at the moment I can't
think of an example of such an event - perhaps that's because there
are none. I'm hoping the brain trust on this list can think of such
an event that I may be overlooking.
|
Help me understand your concerns.
You have embarked on an analytical search for
transient events that might nuisance trip the
fuse. Is there not an equally useful activity
to identify events that might put the proposed
feeder at risk for burning in the first place?
That particular wire between battery feeders and
distribution busses has existed in perhaps a
quarter million production aircraft over the past
80+ years and to my knowledge, has never been fitted
with such protection.
Are you aware of facts that argue with the notion
that hard-faults capable of raising that 6AWG wire
to hazardous temperatures do not exist outside
the realm of poor installation practice?
Bob . . .
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jluckey(at)pacbell.net
Guest
|
| Posted: Fri Dec 06, 2013 8:20 am Post subject: Unprotected Feeder in Z Drawings |
|
|
Bob,
Not sure I would call them "concerns". It's more like playing what-if
based upon my experience in other environments.
In other electrical realms: marine, residential, commercial, and I
worked on a few high-end motor homes, having an un-protected
feeder would be frowned upon (or in varying degrees of
disapproval: considered negligent, unwise, "against code", etc.)
That experience permeates my system design process.
Is there not an equally useful activity to identify events that might put the proposed feeder at risk for burning in the first place?
Certainly, but that doesn't mean that one should not engage
in exploring all options and possibilities.
Are you aware of facts that argue with the notion that hard-faults capable of raising that 6AWG wire to hazardous temperatures do not exist outside the realm of poor installation practice?
I am not. But my ignorance of such information does not mean
that it does not exist.
That particular wire between battery feeders and distribution busses has existed in perhaps a quarter million production aircraft over the past 80+ years and to my knowledge, has never been fitted with such protection.
I find that fascinating...
In my relatively simple mind I consider adding a fuse to the feeder
in question to have little or no down side and potentially huge
upside - preventing an in-flight fire. (not a fan of in-flight fires)
So the downside is that there could be some innocuous event
that I am unaware of which pops the proposed big fuse
unnecessarily. (sounds a little ridiculous, but carry on...)
I can't think of anything like that but I'm not a genius so I
thought I'd throw it out to The List to see if its collective
wisdom knows about something I may have overlooked.
-Jeff
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Friday, December 6, 2013 5:18 AM
Subject: Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
At 12:16 PM 12/5/2013, you wrote:
| Quote: | Ken,
I think you put your finger on it - I'm interested in analyzing the potential for events which are non-catastrophic & transient in nature that might cause the fuse to pop un-necessarily (nuisance trip).
I think that's a pretty small universe and at the moment I can't think of an example of such an event - perhaps that's because there are none. I'm hoping the brain trust on this list can think of such an event that I may be overlooking.
|
Help me understand your concerns.
You have embarked on an analytical search for
transient events that might nuisance trip the
fuse. Is there not an equally useful activity
to identify events that might put the proposed
feeder at risk for burning in the first place?
That particular wire between battery feeders and
distribution busses has existed in perhaps a
quarter million production aircraft over the past
80+ years and to my knowledge, has never been fitted
with such protection.
Are you aware of facts that argue with the notion
that hard-faults capable of raising that 6AWG wire
to hazardous temperatures do not exist outside
the realm of poor installation practice?
Bob . . .
www.aeroelectric.com< * HomebuiltHELP www.mypilotstor &nbs========================
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nuckolls.bob(at)aeroelect
Guest
|
| Posted: Fri Dec 06, 2013 10:30 am Post subject: Unprotected Feeder in Z Drawings |
|
|
| Quote: |
That particular wire between battery feeders and distribution busses
has existed in perhaps a quarter million production aircraft over
the past 80+ years and to my knowledge, has never been fitted with
such protection.
I find that fascinating...
In my relatively simple mind I consider adding a fuse to the feeder
in question to have little or no down side and potentially huge
upside - preventing an in-flight fire. (not a fan of in-flight fires)
|
Consider the consequences of opening that fuse
(or any other event causing that pathway to open)
in a TC aircraft. You loose EVERYTHING on the panel.
I.e. single point of failure for all accessories.
Yeah but . . . if the fuse opens, then there was
something 'wrong'.
Yes, but what? The FEMA process calls for hypothesizing
every kind of event that can open the fuse and either (1)
crafting a plan-b or (2) suppressing the risk.
| Quote: | So the downside is that there could be some innocuous event
that I am unaware of which pops the proposed big fuse
unnecessarily. (sounds a little ridiculous, but carry on...)
I can't think of anything like that but I'm not a genius so I
thought I'd throw it out to The List to see if its collective
wisdom knows about something I may have overlooked.
|
We have a huge data base from which to conduct that
assessment not the least of which are big bunches of
airplanes smaller bunches of qualification studies
and relatively tiny bunches of incidences that bent
aluminum and maybe even broke bones.
The NTSB narrative on aircraft accidents is accessible
here . . .
http://tinyurl.com/pqcdj4h
Do a random search of FINAL REPORTS with your senses
attuned to causation with roots in human failings
(either in operation, maintenance or design) and those
which have causation in some physical failure
mechanism.
Instances that speak to any electrical will fall into
the second category for causation and will be a
minuscule portion of the whole . . . and
of those, faulting of a wire to ground is even
smaller.
In 40 years of flying, 1000+ hrs as pilot and
probably another 2000 as passenger/observer, I've
observed only two incidences of a popped breaker in
flight. NEITHER of those cases had root cause in a
wire faulted to ground - the fault needed to open
your proposed fuse.
The foundation for moving circuit protection off
the panel and reverting back to fuses is predicated
on similar experiences by thousands of other pilots.
Experiences suggesting that dedicating dollars, panel
space, weight and fabrication time to a breaker-panel
is not a good return on investment.
Bottom line is that you're many, many times more
likely to have a bad day in the cockpit for reasons
far removed from a hard ground fault on your 6AWG
bus feeder . . . and THAT because you didn't conduct
due diligence in its installation.
Same thing applies to torque on your prop bolts,
replacing a tire that's flopping cordage, taking
an extra close look at forecasts during icing season,
and a host of things we do that go to reducing
risk.
In the case of the bus feeder, the risks are not
so much to the wire as to the thing the wire touches.
Case in point: C90 on short final experiences disconnect
of elevator cables. Pilot uses trim commands and power to
execute go-around, assesses the condition and successfully
lands the airplane with rudder, trim and power.
Pulling up floorboards in the cockpit revealed a 40A
protected feeder to the windshield de-ice inverter
had been mis-positioned against the elevator control
cable during a maintenance operation. Over what had to
be many hours of operation, motion of the cable wore
through the insulation bringing the cable into contact
with the hot wire. The arcing and sparking was of
insufficient intensity to come to attention of crew
in spite of the fact that it was going on virtually
under their feet.
The copper wire was barely damaged. The breaker never
popped while the elevator cable eventually eroded through
and parted. Compare thermal properties of copper versus
steel . . . this explains why the best steel safes have
intermediate layers of copper in their construction. It's
EASY to burn through steel . . . next to impossible on copper.
This narrative explains the high order probability that
even if you DID get your 6AWG feeder faulted to
ground, it's most likely to be a soft fault that
burns a hole in your airplane while doing little
damage to the wire . . . and certainly far short of
getting it to smoke and/or open a fuse/breaker.
Adding 'protection' to this pathway doubles the
number of joints in the pathway and adds nothing
demonstrable in terms of fault response . . . which
is why the spam-can builders don't do it either.
Bob . . .
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jluckey(at)pacbell.net
Guest
|
| Posted: Fri Dec 06, 2013 5:39 pm Post subject: Unprotected Feeder in Z Drawings |
|
|
Bob,
Ok, I don't disagree w/ any of the points made but let's play the Devil's Advocate/Worst Case Scenario game.
Several years ago in Germany Pilot A was flying an Extra 300 and he looses his pen. He finishes his flight but forgets to recover the pen. A few days later Pilot B takes the plane through several aerobatic maneuvers which dislodge the pen from where it was hiding and wedge it between the buss on the back of the breakers and the airframe causing a fault to ground. Smoke in the cockpit, panic, denial, etc but eventually Pilot B does the right thing and kills the master, lands plane, changes underwear, semi-happy ending. Good News: engine not electrically-dependent so engine keeps running:)
Bad News: The plane requires some serious re-wire because the feeder melted other wires in the loom. Sure, no one died but I certainly don't want to be Pilot B! If that feeder had been fused there would have been no smoke and no damage to wiring.
The point is that simply installing the feeder w/ care & craftsmanship may not be enough. No matter how well that feeder was installed, it would have made no difference in this scenario. Unforeseen circumstances could make for a bad day for your electrical system. It may be impossible to foresee all possible bad scenarios so we want the design of the system to be as fault tolerant as possible.
Perhaps putting a fuse in the feed line may be a "belt & suspenders" approach but I still don't see a real down side and, like I mentioned earlier, I sure don't want to be Pilot B.
BTW Bob (and all) I certainly enjoy being able to explore & discuss these issues in cordial & intelligent ways - whether or not there's a right or wrong answer, I always learn something.
-Jeff
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Friday, December 6, 2013 10:29 AM
Subject: Re: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
| Quote: |
That particular wire between battery feeders and distribution busses has existed in perhaps a quarter million production aircraft over the past 80+ years and to my knowledge, has never been fitted with such protection.
I find that fascinating...
In my relatively simple mind I consider adding a fuse to the feeder
in question to have little or no down side and potentially huge
upside - preventing an in-flight fire. (not a fan of in-flight fires)
|
Consider the consequences of opening that fuse
(or any other event causing that pathway to open)
in a TC aircraft. You loose EVERYTHING on the panel.
I.e. single point of failure for all accessories.
Yeah but . . . if the fuse opens, then there was
something 'wrong'.
Yes, but what? The FEMA process calls for hypothesizing
every kind of event that can open the fuse and either (1)
crafting a plan-b or (2) suppressing the risk.
| Quote: | So the downside is that there could be some innocuous event
that I am unaware of which pops the proposed big fuse
unnecessarily. (sounds a little ridiculous, but carry on...)
I can't think of anything like that but I'm not a genius so I
thought I'd throw it out to The List to see if its collective
wisdom knows about something I may have overlooked.
|
We have a huge data base from which to conduct that
assessment not the least of which are big bunches of
airplanes smaller bunches of qualification studies
and relatively tiny bunches of incidences that bent
aluminum and maybe even broke bones.
The NTSB narrative on aircraft accidents is accessible
here . . .
http://tinyurl.com/pqcdj4h
Do a random search of FINAL REPORTS with your senses
attuned to causation with roots in human failings
(either in operation, maintenance or design) and those
which have causation in some physical failure
mechanism.
Instances that speak to any electrical will fall into
the second category for causation and will be a
minuscule portion of the whole . . . and
of those, faulting of a wire to ground is even
smaller.
In 40 years of flying, 1000+ hrs as pilot and
probably another 2000 as passenger/observer, I've
observed only two incidences of a popped breaker in
flight. NEITHER of those cases had root cause in a
wire faulted to ground - the fault needed to open
your proposed fuse.
The foundation for moving circuit protection off
the panel and reverting back to fuses is predicated
on similar experiences by thousands of other pilots.
Experiences suggesting that dedicating dollars, panel
space, weight and fabrication time to a breaker-panel
is not a good return on investment.
Bottom line is that you're many, many times more
likely to have a bad day in the cockpit for reasons
far removed from a hard ground fault on your 6AWG
bus feeder . . . and THAT because you didn't conduct
due diligence in its installation.
Same thing applies to torque on your prop bolts,
replacing a tire that's flopping cordage, taking
an extra close look at forecasts during icing season,
and a host of things we do that go to reducing
risk.
In the case of the bus feeder, the risks are not
so much to the wire as to the thing the wire touches.
Case in point: C90 on short final experiences disconnect
of elevator cables. Pilot uses trim commands and power to
execute go-around, assesses the condition and successfully
lands the airplane with rudder, trim and power.
Pulling up floorboards in the cockpit revealed a 40A
protected feeder to the windshield de-ice inverter
had been mis-positioned against the elevator control
cable during a maintenance operation. Over what had to
be many hours of operation, motion of the cable wore
through the insulation bringing the cable into contact
with the hot wire. The arcing and sparking was of
insufficient intensity to come to attention of crew
in spite of the fact that it was going on virtually
under their feet.
The copper wire was barely damaged. The breaker never
popped while the elevator cable eventually eroded through
and parted. Compare thermal properties of copper versus
steel . . . this explains why the best steel safes have
intermediate layers of copper in their construction. It's
EASY to burn through steel . . . next to impossible on copper.
This narrative explains the high order probability that
even if you DID get your 6AWG feeder faulted to
ground, it's most likely to be a soft fault that
burns a hole in your airplane while doing little
damage to the wire . . . and certainly far short of
getting it to smoke and/or open a fuse/breaker.
Adding 'protection' to this pathway doubles the
number of joints in the pathway and adds nothing
demonstrable in terms of fault response . . . which
is why the spam-can builders don't do it either.
Bob . . .
http://www.matronics.com/Navigator?AeroElectric-Lista href="http://forums.matronics.com/" target="_blank">http://forums.mat====================
[quote][b]
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jan(at)CLAVER.DEMON.CO.UK
Guest
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| Posted: Sat Dec 07, 2013 3:12 am Post subject: Unprotected Feeder in Z Drawings |
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Hi Jeff,
Interesting story. My take on this is simply a question of ‘risk management’. Lets say that ALL planes that do not have this ‘extra fuse’ now suddenly get this ‘extra fuse’ .. do you think the risk is higher that something goes wrong with the fuse .. the extra connectors to fit the fuse .. how the fuse is fitted .. how it is potentially fitted incorrectly etc…
IF .. the only case of ‘something bad happened because this wire is not fused’ is the incident that you mention below .. Well … what do you think is more likely to happen ….
Something wrong will all the 1000 of planes that now have ‘one more part that can go wrong’ i.e. the extra fuse … or a pen or something else lodging against the bus and shorting to ground ?
On YOUR plane … how easy is it for anything to actually lodge in the same place ? Suggest looking at best way to prevent something to lodge and short .. than to add something that has never been seen a ‘required’ before ….
I agree that there are very few things that are absolutely right or absolutely wrong .. (apart from when at school …then everything was always very black and white .
The more you can ‘remove from the plane’ the less you have that can go wrong … what you are ‘left with’ …well .. you just need to analyze the risk and what happens when it fail .. can you reduce the risk … without adding another risk ..
The following is not related to aircrafts . but I like to use it to make people thing about risk .. and how to reduce accidents …. I have no idea if it would work .. but you could argue the case .
The general thought of car safety is to add more things .. seat belts – airbags – crumble zones etc etc.. list goes on and on …
The net results is that we tend to drive faster .. We have more accidents .. maybe less people would die .. but then compared to what ?
Here is my idea for the ultimate car safety device .. You remove seat belts and you make it a legal requirement that ALL steering wheels must have a 6” spike mounted in the centre .. pointing straight at your chest .. (and NO .. you can not wear a bullet proof west J ..)
Now you know … if you do not drive very carefully, no hard braking etc… … you are not going to last very long are you ? Looking at that 6” spike at the steering wheel.
Sure some people will die ..and some people who are driving very carefully will be hit by someone who does not … But will the OVERALL number of accidents go up or go down ??
J
Enjoy the weekend ! I
Jan
PS : will not be fitting a fuse on that wire … But I will look very very closely at how it is run …..
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Jeff Luckey
Sent: 07 December 2013 01:38
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
Bob,
Ok, I don't disagree w/ any of the points made but let's play the Devil's Advocate/Worst Case Scenario game.
Several years ago in Germany Pilot A was flying an Extra 300 and he looses his pen. He finishes his flight but forgets to recover the pen. A few days later Pilot B takes the plane through several aerobatic maneuvers which dislodge the pen from where it was hiding and wedge it between the buss on the back of the breakers and the airframe causing a fault to ground. Smoke in the cockpit, panic, denial, etc but eventually Pilot B does the right thing and kills the master, lands plane, changes underwear, semi-happy ending. Good News: engine not electrically-dependent so engine keeps running:)
Bad News: The plane requires some serious re-wire because the feeder melted other wires in the loom. Sure, no one died but I certainly don't want to be Pilot B! If that feeder had been fused there would have been no smoke and no damage to wiring.
The point is that simply installing the feeder w/ care & craftsmanship may not be enough. No matter how well that feeder was installed, it would have made no difference in this scenario. Unforeseen circumstances could make for a bad day for your electrical system. It may be impossible to foresee all possible bad scenarios so we want the design of the system to be as fault tolerant as possible.
Perhaps putting a fuse in the feed line may be a "belt & suspenders" approach but I still don't see a real down side and, like I mentioned earlier, I sure don't want to be Pilot B.
BTW Bob (and all) I certainly enjoy being able to explore & discuss these issues in cordial & intelligent ways - whether or not there's a right or wrong answer, I always learn something.
-Jeff
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Friday, December 6, 2013 10:29 AM
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
>
> That particular wire between battery feeders and distribution busses has existed in perhaps a quarter million production aircraft over the past 80+ years and to my knowledge, has never been fitted with such protection.
>
> I find that fascinating...
>
> In my relatively simple mind I consider adding a fuse to the feeder
> in question to have little or no down side and potentially huge
> upside - preventing an in-flight fire. (not a fan of in-flight fires)
Consider the consequences of opening that fuse
(or any other event causing that pathway to open)
in a TC aircraft. You loose EVERYTHING on the panel.
I.e. single point of failure for all accessories.
Yeah but . . . if the fuse opens, then there was
something 'wrong'.
Yes, but what? The FEMA process calls for hypothesizing
every kind of event that can open the fuse and either (1)
crafting a plan-b or (2) suppressing the risk.
> So the downside is that there could be some innocuous event
> that I am unaware of which pops the proposed big fuse
> unnecessarily. (sounds a little ridiculous, but carry on...)
> I can't think of anything like that but I'm not a genius so I
> thought I'd throw it out to The List to see if its collective
> wisdom knows about something I may have overlooked.
We have a huge data base from which to conduct that
assessment not the least of which are big bunches of
airplanes smaller bunches of qualification studies
and relatively tiny bunches of incidences that bent
aluminum and maybe even broke bones.
The NTSB narrative on aircraft accidents is accessible
here . . .
http://tinyurl.com/pqcdj4h
Do a random search of FINAL REPORTS with your senses
attuned to causation with roots in human failings
(either in operation, maintenance or design) and those
which have causation in some physical failure
mechanism.
Instances that speak to any electrical will fall into
the second category for causation and will be a
minuscule portion of the whole . . . and
of those, faulting of a wire to ground is even
smaller.
In 40 years of flying, 1000+ hrs as pilot and
probably another 2000 as passenger/observer, I've
observed only two incidences of a popped breaker in
flight. NEITHER of those cases had root cause in a
wire faulted to ground - the fault needed to open
your proposed fuse.
The foundation for moving circuit protection off
the panel and reverting back to fuses is predicated
on similar experiences by thousands of other pilots.
Experiences suggesting that dedicating dollars, panel
space, weight and fabrication time to a breaker-panel
is not a good return on investment.
Bottom line is that you're many, many times more
likely to have a bad day in the cockpit for reasons
far removed from a hard ground fault on your 6AWG
bus feeder . . . and THAT because you didn't conduct
due diligence in its installation.
Same thing applies to torque on your prop bolts,
replacing a tire that's flopping cordage, taking
an extra close look at forecasts during icing season,
and a host of things we do that go to reducing
risk.
In the case of the bus feeder, the risks are not
so much to the wire as to the thing the wire touches.
Case in point: C90 on short final experiences disconnect
of elevator cables. Pilot uses trim commands and power to
execute go-around, assesses the condition and successfully
lands the airplane with rudder, trim and power.
Pulling up floorboards in the cockpit revealed a 40A
protected feeder to the windshield de-ice inverter
had been mis-positioned against the elevator control
cable during a maintenance operation. Over what had to
be many hours of operation, motion of the cable wore
through the insulation bringing the cable into contact
with the hot wire. The arcing and sparking was of
insufficient intensity to come to attention of crew
in spite of the fact that it was going on virtually
under their feet.
The copper wire was barely damaged. The breaker never
popped while the elevator cable eventually eroded through
and parted. Compare thermal properties of copper versus
steel . . . this explains why the best steel safes have
intermediate layers of copper in their construction. It's
EASY to burn through steel . . . next to impossible on copper.
This narrative explains the high order probability that
even if you DID get your 6AWG feeder faulted to
ground, it's most likely to be a soft fault that
burns a hole in your airplane while doing little
damage to the wire . . . and certainly far short of
getting it to smoke and/or open a fuse/breaker.
Adding 'protection' to this pathway doubles the
number of joints in the pathway and adds nothing
demonstrable in terms of fault response . . . which
is why the spam-can builders don't do it either.
Bob . . .
http://www.matronics.com/Navigator?AeroElectric-Lista href="http://forums.matronics.com/" target="_blank">http://forums.mat====================
0123456789012345678901234567890
[quote][b]
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klehman(at)albedo.net
Guest
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| Posted: Sat Dec 07, 2013 4:29 am Post subject: Unprotected Feeder in Z Drawings |
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OTOH with Blue Sea type remote fuse panels installed at the battery, I
have no exposed bus bars. Feeders to the fuse panels are a couple of
inches long but not exposed. My starter feeder is hot when the master is
on but no big deal turning off the master in flight for me if need be.
So no exposed always hot feeders and no CB's cluttering up the
instrument panel.
Ken
On 06/12/2013 8:38 PM, Jeff Luckey wrote:
| Quote: | Bob,
Ok, I don't disagree w/ any of the points made but let's play the
Devil's Advocate/Worst Case Scenario game.
Several years ago in Germany Pilot A was flying an Extra 300 and he
looses his pen. He finishes his flight but forgets to recover the pen.
A few days later Pilot B takes the plane through several aerobatic
maneuvers which dislodge the pen from where it was hiding and wedge it
between the buss on the back of the breakers and the airframe causing a
fault to ground. Smoke in the cockpit, panic, denial, etc but
eventually Pilot B does the right thing and kills the master, lands
plane, changes underwear, semi-happy ending. Good News: engine not
electrically-dependent so engine keeps running:)
Bad News: The plane requires some serious re-wire because the feeder
melted other wires in the loom. Sure, no one died but I certainly don't
want to be Pilot B! If that feeder had been fused there would have been
no smoke and no damage to wiring.
The point is that simply installing the feeder w/ care & craftsmanship
may not be enough. No matter how well that feeder was installed, it
would have made no difference in this scenario. Unforeseen
circumstances could make for a bad day for your electrical system. It
may be impossible to foresee all possible bad scenarios so we want the
design of the system to be as fault tolerant as possible.
Perhaps putting a fuse in the feed line may be a "belt & suspenders"
approach but I still don't see a real down side and, like I mentioned
earlier, I sure don't want to be Pilot B.
BTW Bob (and all) I certainly enjoy being able to explore & discuss
these issues in cordial & intelligent ways - whether or not there's a
right or wrong answer, I always learn something.
-Jeff
|
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user9253
Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan
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| Posted: Sat Dec 07, 2013 7:09 am Post subject: Re: Unprotected Feeder in Z Drawings |
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If there is a concern about the main feeder shorting to ground, how about making sure that does not happen instead of adding a fuse? The feeder could be double insulated where it passes through the firewall. The circuit breaker bus bar can be insulated. Or better yet, use an insulated fuse block with no exposed bus.
Even if the main feeder was protected with a fuse, there is no guarantee that the fuse will blow in the event of a short circuit. Large fuses are difficult to blow. Many times a short circuit will arc and burn away metal until the short clears itself, without blowing a fuse.
It is good to question why something has always been done a certain way. On the other hand, it is hard to argue with success.
Joe
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sat Dec 07, 2013 9:31 am Post subject: Unprotected Feeder in Z Drawings |
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At 07:38 PM 12/6/2013, you wrote:
| Quote: | Bob,
Ok, I don't disagree w/ any of the points made but let's play the
Devil's Advocate/Worst Case Scenario game.
Several years ago in Germany Pilot A was flying an Extra 300 and he
looses his pen. He finishes his flight but forgets to recover the
pen. A few days later Pilot B takes the plane through several
aerobatic maneuvers which dislodge the pen from where it was hiding
and wedge it between the buss on the back of the breakers and the
airframe causing a fault to ground. Smoke in the cockpit, panic,
denial, etc but eventually Pilot B does the right thing and kills
the master, lands plane, changes underwear, semi-happy ending. Good
News: engine not electrically-dependent so engine keeps running:)
Bad News: The plane requires some serious re-wire because the feeder
melted other wires in the loom. Sure, no one died but I certainly
don't want to be Pilot B! If that feeder had been fused there would
have been no smoke and no damage to wiring.
|
Okay! A hypothesis. This is step-one in the conduct
of an FMEA for a unique event. Let's apply what we know
about the nature of things and machines to expand our
understanding of this hypothesis and to craft a
reasoned reaction to the result.
I am skeptical of this story based on the limited
data offered . . . which is not unusual. 99.9% of
what I call dark-n-stormy-night stories in the journals
are long on story value and short on data . . . the
narrative of this incident is no different.
Let us consider the processes we have evolved for
the purpose of making secure connections between
fat-wires and some terminus . . . usually a threaded
fastener.
The design goal is to achieve a sub-milliohm connection
between all conductors such that temperature rise at
the connections does not contribute to long term effects
of accelerated corrosion and ultimate failure of the
joint.
I have seen numerous examples of failure-to-implement-
good-practice as manifest by studs burned off, nuts
arc welded to studs, terminals damaged beyond serviceable
condition, etc. Except for the effects of localize heating
at the failed joint, the WIRE crimped into that terminal
was not affected. This is because the dissipation of energy
occurs at the POINT OF HIGHEST RESISTANCE in the loop.
Do the study sometime to figure out why a long piece
of wire suspended between two terminals always burns through
near the center every time.
Okay, consider the rogue debris looking for a place to
do mischief. Aha! exposed bus bar and bare airframe . . .
ideal. Consider the mechanism that brings a metallic
pen into contact with bus and airframe with such conductive
integrity that it places a span of wire at risk . . .
and outlasts the wire during the ensuing contest of
smoke and fire.
The pen would have to (1) possess conductivity capabilities
on a par or better than the at-risk wire and (2) be
held in contact with bus and airframe with sub-milliohm
integrity for a length of time necessary to heat other
components to destructive temperatures.
Another question arising from the narrative is based on
the statement: "The plane requires some serious re-wire
because the feeder melted other wires in the loom."
Again, how did the rogue debris achieve conductive
integrity that had to be a small fraction of that
for the wire(s) being overloaded?
Risks to underwear not withstanding, this pilot's airplane
was obviously wired with attention to the needs of an
electrically dependent engine that was not influenced
by the position of the master switch.
This story yields to a simple study of "where does
the energy go?" Another example: I remember 1969 when
Gordon Wood put a peak-measuring voltmeter on the coil of a
contactor and discovered, "Great galloping gremlins
Batman! Did you see that?"
Yes, discovery of those numbers in a system fitted with
newly minted, solid state radios gave rise for much
concern. But as Gordon deduced (and we've confirmed
in recent years) the energy did not propagate out
onto the bus and is of greatest risk to the controlling
device (master and starter switches). Further, adding
the $1 diode across the coil put that dragon to bed
forever.
Details of simple-ideas aside, the hypothesis you proffered
is a valid component of the FMEA process. It highlighted
something I neglected to included in my earlier
listing of potential risks to pieces of the airplane
with secondary risks to exposed conductors. I neglected
to include loose articles.
The FMEA has to consider not only the details of
how the risks stack together but the environment in
which they occur. Our el-cheepo aerial targets at
Beech were heavily controlled for high reliability (low
risk) missions. Why all the fuss? It's not a man-rated
piece of hardware and expendable. Easy. The $ expended
to set up a mission in which this target would be used
was huge. It orchestrated movements of ships a sea,
flights of training aircraft, called for an accurate
launch of the target from 50,000ft and M1.5 to fly down
a precise track, etc. The expenditures of mission
resources far exceeded the price of our little piece
of throw-away hardware by factors of 1000:1.
Okay, back to your proposed project and concerns for
system reliability. It's not a man-rated weapon so
those sorts of issues don't apply. Do you plan to
conduct negative-g aerobatics wherein loose items
would become a consideration? It would be interesting
if we could search the accident database looking for
incidents where loose articles were major players
in the evolution or outcome of an event. But
for sure, GA aircraft from C-150 to G-5 are seldom
involved in negative-g events . . . and when they
are . . . it's probably not a piece of loose hardware
that drives the outcome.
I advise caution for incorporating 'common knowledge'
into one's deliberations that will burden empty weight, time,
and dollars to reduce risks. You can do a Google search
on my website for these statements:
"I had a Seawind in here yesterday with lots of tiny breakers that
pop all the time. Was a real hassle to work on. Just because a 3 amp
fuse won't blow until it gets to 4 amps isn't the point (which is
known by everyone who deal with these things)"
"Main power bus is fused at 35 Amperes"
"Remember, a fuse or breaker won't hold above 80% of what it says on
the nameplate; so a 50 Amp breaker will pop at 40 amps after 20 or 30 minutes."
. . . which are a small sample of what was widely
distributed as useful information . . . and made yours
truly the target of incoming sand and tomatoes
pitched by acolytes of the author when I questioned the
simple-ideas that supported his statements.
Don't give up on this my friend. If there's a risk yet
un-identified, we all have an interest in knowing what
it is and deducing a mitigating response. At the same
time, be a good scientist. Exploit those recipes for
success with good track records but remain eternally
skeptical of that which is assumed to be valid. The simple-
ideas from which a recipe is crafted are inviolate and
unchanging. It's our skill and understanding of how those
simple-ideas fit together that can get wobbly. They
are always worthy of either re-validation or discounted for
something better.
Bob . . .
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nuckolls.bob(at)aeroelect
Guest
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| Posted: Sat Dec 07, 2013 9:39 am Post subject: Unprotected Feeder in Z Drawings |
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| Quote: |
Here is my idea for the ultimate car safety device .. You remove seat belts and you make it a legal requirement that ALL steering wheels must have a 6 spike mounted in the centre .. pointing straight at your chest . (and NO .. you can not wear a bullet proof west J ..)
Now you know if you do not drive very carefully, no hard braking etc you are not going to last very long are you ? Looking at that 6 spike at the steering wheel.
Sure some people will die ..and some people who are driving very carefully will be hit by someone who does not But will the OVERALL number of accidents go up or go down ?? |
Excellent question!
An illuminating peek into the innate perversity of
the human condition. I spent a number of years in
the investigation and modeling of events surrounding
accidents at railroad grade crossings. Cross-bucks
are mandated at every crossing. Some crossings get
lights. Some get lights and gates. The budget for
upgrading safety hardware at the crossing was limited
so only the worst crossings got the full treatment.
It was interesting to note that after gates were
installed at crossings with the highest accident
rates, number of accidents at the crossing only
dropped by half.
Bob . . . [quote][b]
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mrspudandcompany(at)veriz
Guest
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| Posted: Sat Dec 07, 2013 10:38 am Post subject: Unprotected Feeder in Z Drawings |
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| Quote: | It was interesting to note that after gates were
installed at crossings with the highest accident
rates, number of accidents at the crossing only
dropped by half
| Quote: | You reach a point of no return when you try
to protect people from themselves and their
own stupidity. Granted, some things can
not be avoided, but we now live in a society
where responsibility belongs to someone
else.
Roger
|
|
I am using the Free version of SPAMfighter.SPAMfighter has removed 1588 of my spam emails to date.Do you have a slow PC? Try a free scan! [quote][b]
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jluckey(at)pacbell.net
Guest
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| Posted: Sat Dec 07, 2013 1:23 pm Post subject: Unprotected Feeder in Z Drawings |
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Jan,
I'm not sure if you are being serious in this quote (perhaps you were being facetious?):
The general thought of car safety is to add more things .. seat belts – airbags – crumble zones etc etc.. list goes on and on …
The net results is that we tend to drive faster .. We have more accidents .. maybe less people would die .. but then compared to what ?
If you are suggesting that technology has not made cars safer, that would be an inaccurate assertion. The advances in motor vehicle safety that you cite have increased safety tremendously. See:
http://www-fars.nhtsa.dot.gov/Main/index.aspx
Accident rates have plummeted over the past 20 years despite large increases in the number of vehicles. Automotive safety is fantastic example of making things safer by applying technology.
...
From: jan <jan(at)claver.demon.co.uk>
To: aeroelectric-list(at)matronics.com
Sent: Saturday, December 7, 2013 3:22 AM
Subject: RE: AeroElectric-List: Unprotected Feeder in Z Drawings
Hi Jeff,
Interesting story. My take on this is simply a question of ‘risk management’. Lets say that ALL planes that do not have this ‘extra fuse’ now suddenly get this ‘extra fuse’ .. do you think the risk is higher that something goes wrong with the fuse .. the extra connectors to fit the fuse .. how the fuse is fitted .. how it is potentially fitted incorrectly etc…
IF .. the only case of ‘something bad happened because this wire is not fused’ is the incident that you mention below .. Well … what do you think is more likely to happen ….
Something wrong will all the 1000 of planes that now have ‘one more part that can go wrong’ i.e. the extra fuse … or a pen or something else lodging against the bus and shorting to ground ?
On YOUR plane … how easy is it for anything to actually lodge in the same place ? Suggest looking at best way to prevent something to lodge and short .. than to add something that has never been seen a ‘required’ before ….
I agree that there are very few things that are absolutely right or absolutely wrong .. (apart from when at school …then everything was always very black and white ..
The more you can ‘remove from the plane’ the less you have that can go wrong … what you are ‘left with’ …well .. you just need to analyze the risk and what happens when it fail .. can you reduce the risk … without adding another risk ..
The following is not related to aircrafts .. but I like to use it to make people thing about risk .. and how to reduce accidents …. I have no idea if it would work .. but you could argue the case ..
The general thought of car safety is to add more things .. seat belts – airbags – crumble zones etc etc.. list goes on and on …
The net results is that we tend to drive faster .. We have more accidents .. maybe less people would die .. but then compared to what ?
Here is my idea for the ultimate car safety device .. You remove seat belts and you make it a legal requirement that ALL steering wheels must have a 6” spike mounted in the centre .. pointing straight at your chest .. (and NO .. you can not wear a bullet proof west J ..)
Now you know … if you do not drive very carefully, no hard braking etc… … you are not going to last very long are you ? Looking at that 6” spike at the steering wheel.
Sure some people will die ..and some people who are driving very carefully will be hit by someone who does not … But will the OVERALL number of accidents go up or go down ??
J
Enjoy the weekend ! I
Jan
PS : will not be fitting a fuse on that wire … But I will look very very closely at how it is run …..
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Jeff Luckey
Sent: 07 December 2013 01:38
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
Bob,
Ok, I don't disagree w/ any of the points made but let's play the Devil's Advocate/Worst Case Scenario game.
Several years ago in Germany Pilot A was flying an Extra 300 and he looses his pen. He finishes his flight but forgets to recover the pen. A few days later Pilot B takes the plane through several aerobatic maneuvers which dislodge the pen from where it was hiding and wedge it between the buss on the back of the breakers and the airframe causing a fault to ground. Smoke in the cockpit, panic, denial, etc but eventually Pilot B does the right thing and kills the master, lands plane, changes underwear, semi-happy ending. Good News: engine not electrically-dependent so engine keeps running:)
Bad News: The plane requires some serious re-wire because the feeder melted other wires in the loom. Sure, no one died but I certainly don't want to be Pilot B! If that feeder had been fused there would have been no smoke and no damage to wiring.
The point is that simply installing the feeder w/ care & craftsmanship may not be enough. No matter how well that feeder was installed, it would have made no difference in this scenario. Unforeseen circumstances could make for a bad day for your electrical system. It may be impossible to foresee all possible bad scenarios so we want the design of the system to be as fault tolerant as possible.
Perhaps putting a fuse in the feed line may be a "belt & suspenders" approach but I still don't see a real down side and, like I mentioned earlier, I sure don't want to be Pilot B.
BTW Bob (and all) I certainly enjoy being able to explore & discuss these issues in cordial & intelligent ways - whether or not there's a right or wrong answer, I always learn something.
-Jeff
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Friday, December 6, 2013 10:29 AM
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
>
> That particular wire between battery feeders and distribution busses has existed in perhaps a quarter million production aircraft over the past 80+ years and to my knowledge, has never been fitted with such protection.
>
> I find that fascinating...
>
> In my relatively simple mind I consider adding a fuse to the feeder
> in question to have little or no down side and potentially huge
> upside - preventing an in-flight fire. (not a fan of in-flight fires)
Consider the consequences of opening that fuse
(or any other event causing that pathway to open)
in a TC aircraft. You loose EVERYTHING on the panel.
I.e. single point of failure for all accessories.
Yeah but . . . if the fuse opens, then there was
something 'wrong'.
Yes, but what? The FEMA process calls for hypothesizing
every kind of event that can open the fuse and either (1)
crafting a plan-b or (2) suppressing the risk.
> So the downside is that there could be some innocuous event
> that I am unaware of which pops the proposed big fuse
> unnecessarily. (sounds a little ridiculous, but carry on...)
> I can't think of anything like that but I'm not a genius so I
> thought I'd throw it out to The List to see if its collective
> wisdom knows about something I may have overlooked.
We have a huge data base from which to conduct that
assessment not the least of which are big bunches of
airplanes smaller bunches of qualification studies
and relatively tiny bunches of incidences that bent
aluminum and maybe even broke bones.
The NTSB narrative on aircraft accidents is accessible
here . . .
http://tinyurl.com/pqcdj4h
Do a random search of FINAL REPORTS with your senses
attuned to causation with roots in human failings
(either in operation, maintenance or design) and those
which have causation in some physical failure
mechanism.
Instances that speak to any electrical will fall into
the second category for causation and will be a
minuscule portion of the whole . . . and
of those, faulting of a wire to ground is even
smaller.
In 40 years of flying, 1000+ hrs as pilot and
probably another 2000 as passenger/observer, I've
observed only two incidences of a popped breaker in
flight. NEITHER of those cases had root cause in a
wire faulted to ground - the fault needed to open
your proposed fuse.
The foundation for moving circuit protection off
the panel and reverting back to fuses is predicated
on similar experiences by thousands of other pilots.
Experiences suggesting that dedicating dollars, panel
space, weight and fabrication time to a breaker-panel
is not a good return on investment.
Bottom line is that you're many, many times more
likely to have a bad day in the cockpit for reasons
far removed from a hard ground fault on your 6AWG
bus feeder . . . and THAT because you didn't conduct
due diligence in its installation.
Same thing applies to torque on your prop bolts,
replacing a tire that's flopping cordage, taking
an extra close look at forecasts during icing season,
and a host of things we do that go to reducing
risk.
In the case of the bus feeder, the risks are not
so much to the wire as to the thing the wire touches.
Case in point: C90 on short final experiences disconnect
of elevator cables. Pilot uses trim commands and power to
execute go-around, assesses the condition and successfully
lands the airplane with rudder, trim and power.
Pulling up floorboards in the cockpit revealed a 40A
protected feeder to the windshield de-ice inverter
had been mis-positioned against the elevator control
cable during a maintenance operation. Over what had to
be many hours of operation, motion of the cable wore
through the insulation bringing the cable into contact
with the hot wire. The arcing and sparking was of
insufficient intensity to come to attention of crew
in spite of the fact that it was going on virtually
under their feet.
The copper wire was barely damaged. The breaker never
popped while the elevator cable eventually eroded through
and parted. Compare thermal properties of copper versus
steel . . . this explains why the best steel safes have
intermediate layers of copper in their construction. It's
EASY to burn through steel . . . next to impossible on copper.
This narrative explains the high order probability that
even if you DID get your 6AWG feeder faulted to
ground, it's most likely to be a soft fault that
burns a hole in your airplane while doing little
damage to the wire . . . and certainly far short of
getting it to smoke and/or open a fuse/breaker.
Adding 'protection' to this pathway doubles the
number of joints in the pathway and adds nothing
demonstrable in terms of fault response . . . which
is why the spam-can builders don't do it either.
Bob . . .
http://www.matronics.com/Navigator?AeroElectric-Lista href="http://forums.matronics.com/" target="_blank">http://forums.mat====================
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jan(at)CLAVER.DEMON.CO.UK
Guest
|
| Posted: Sat Dec 07, 2013 2:20 pm Post subject: Unprotected Feeder in Z Drawings |
|
|
Jeff,
J
Of course I rather have a crash in a car that has seat belts (as I always wear them ....)
My point is that we add technical things .. to ‘protect us’ ... We could be equally safe if we took responsibility and drove in such a way that we did not have accidents – or at least had a lot less .
Jan
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Jeff Luckey
Sent: 07 December 2013 21:22
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
Jan,
I'm not sure if you are being serious in this quote (perhaps you were being facetious?):
The general thought of car safety is to add more things .. seat belts – airbags – crumble zones etc etc.. list goes on and on …
The net results is that we tend to drive faster .. We have more accidents .. maybe less people would die .. but then compared to what ?
If you are suggesting that technology has not made cars safer, that would be an inaccurate assertion. The advances in motor vehicle safety that you cite have increased safety tremendously. See:
http://www-fars.nhtsa.dot.gov/Main/index.aspx
Accident rates have plummeted over the past 20 years despite large increases in the number of vehicles. Automotive safety is fantastic example of making things safer by applying technology.
...
From: jan <jan(at)claver.demon.co.uk>
To: aeroelectric-list(at)matronics.com
Sent: Saturday, December 7, 2013 3:22 AM
Subject: RE: AeroElectric-List: Unprotected Feeder in Z Drawings
Hi Jeff,
Interesting story. My take on this is simply a question of ‘risk management’. Lets say that ALL planes that do not have this ‘extra fuse’ now suddenly get this ‘extra fuse’ .. do you think the risk is higher that something goes wrong with the fuse . the extra connectors to fit the fuse .. how the fuse is fitted .. how it is potentially fitted incorrectly etc…
IF .. the only case of ‘something bad happened because this wire is not fused’ is the incident that you mention below .. Well … what do you think is more likely to happen ….
Something wrong will all the 1000 of planes that now have ‘one more part that can go wrong’ i.e. the extra fuse … or a pen or something else lodging against the bus and shorting to ground ?
On YOUR plane … how easy is it for anything to actually lodge in the same place ? Suggest looking at best way to prevent something to lodge and short .. than to add something that has never been seen a ‘required’ before ….
I agree that there are very few things that are absolutely right or absolutely wrong .. (apart from when at school …then everything was always very black and white ..
The more you can ‘remove from the plane’ the less you have that can go wrong … what you are ‘left with’ …well .. you just need to analyze the risk and what happens when it fail .. can you reduce the risk … without adding another risk ..
The following is not related to aircrafts .. but I like to use it to make people thing about risk .. and how to reduce accidents …. I have no idea if it would work .. but you could argue the case ..
The general thought of car safety is to add more things .. seat belts – airbags – crumble zones etc etc.. list goes on and on …
The net results is that we tend to drive faster .. We have more accidents .. maybe less people would die .. but then compared to what ?
Here is my idea for the ultimate car safety device .. You remove seat belts and you make it a legal requirement that ALL steering wheels must have a 6” spike mounted in the centre . pointing straight at your chest .. (and NO .. you can not wear a bullet proof west J ..)
Now you know … if you do not drive very carefully, no hard braking etc… … you are not going to last very long are you ? Looking at that 6” spike at the steering wheel.
Sure some people will die .and some people who are driving very carefully will be hit by someone who does not … But will the OVERALL number of accidents go up or go down ??
J
Enjoy the weekend ! I
Jan
PS : will not be fitting a fuse on that wire … But I will look very very closely at how it is run …..
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Jeff Luckey
Sent: 07 December 2013 01:38
To: aeroelectric-list(at)matronics.com
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
Bob,
Ok, I don't disagree w/ any of the points made but let's play the Devil's Advocate/Worst Case Scenario game.
Several years ago in Germany Pilot A was flying an Extra 300 and he looses his pen. He finishes his flight but forgets to recover the pen. A few days later Pilot B takes the plane through several aerobatic maneuvers which dislodge the pen from where it was hiding and wedge it between the buss on the back of the breakers and the airframe causing a fault to ground. Smoke in the cockpit, panic, denial, etc but eventually Pilot B does the right thing and kills the master, lands plane, changes underwear, semi-happy ending. Good News: engine not electrically-dependent so engine keeps running:)
Bad News: The plane requires some serious re-wire because the feeder melted other wires in the loom. Sure, no one died but I certainly don't want to be Pilot B! If that feeder had been fused there would have been no smoke and no damage to wiring.
The point is that simply installing the feeder w/ care & craftsmanship may not be enough. No matter how well that feeder was installed, it would have made no difference in this scenario. Unforeseen circumstances could make for a bad day for your electrical system. It may be impossible to foresee all possible bad scenarios so we want the design of the system to be as fault tolerant as possible.
Perhaps putting a fuse in the feed line may be a "belt & suspenders" approach but I still don't see a real down side and, like I mentioned earlier, I sure don't want to be Pilot B.
BTW Bob (and all) I certainly enjoy being able to explore & discuss these issues in cordial & intelligent ways - whether or not there's a right or wrong answer, I always learn something.
-Jeff
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>
To: aeroelectric-list(at)matronics.com
Sent: Friday, December 6, 2013 10:29 AM
Subject: Re: AeroElectric-List: Unprotected Feeder in Z Drawings
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)>
>
> That particular wire between battery feeders and distribution busses has existed in perhaps a quarter million production aircraft over the past 80+ years and to my knowledge, has never been fitted with such protection.
>
> I find that fascinating...
>
> In my relatively simple mind I consider adding a fuse to the feeder
> in question to have little or no down side and potentially huge
> upside - preventing an in-flight fire. (not a fan of in-flight fires)
Consider the consequences of opening that fuse
(or any other event causing that pathway to open)
in a TC aircraft. You loose EVERYTHING on the panel.
I.e. single point of failure for all accessories.
Yeah but . . . if the fuse opens, then there was
something 'wrong'.
Yes, but what? The FEMA process calls for hypothesizing
every kind of event that can open the fuse and either (1)
crafting a plan-b or (2) suppressing the risk.
> So the downside is that there could be some innocuous event
> that I am unaware of which pops the proposed big fuse
> unnecessarily. (sounds a little ridiculous, but carry on...)
> I can't think of anything like that but I'm not a genius so I
> thought I'd throw it out to The List to see if its collective
> wisdom knows about something I may have overlooked.
We have a huge data base from which to conduct that
assessment not the least of which are big bunches of
airplanes smaller bunches of qualification studies
and relatively tiny bunches of incidences that bent
aluminum and maybe even broke bones.
The NTSB narrative on aircraft accidents is accessible
here . . .
http://tinyurl.com/pqcdj4h
Do a random search of FINAL REPORTS with your senses
attuned to causation with roots in human failings
(either in operation, maintenance or design) and those
which have causation in some physical failure
mechanism.
Instances that speak to any electrical will fall into
the second category for causation and will be a
minuscule portion of the whole . . . and
of those, faulting of a wire to ground is even
smaller.
In 40 years of flying, 1000+ hrs as pilot and
probably another 2000 as passenger/observer, I've
observed only two incidences of a popped breaker in
flight. NEITHER of those cases had root cause in a
wire faulted to ground - the fault needed to open
your proposed fuse.
The foundation for moving circuit protection off
the panel and reverting back to fuses is predicated
on similar experiences by thousands of other pilots.
Experiences suggesting that dedicating dollars, panel
space, weight and fabrication time to a breaker-panel
is not a good return on investment.
Bottom line is that you're many, many times more
likely to have a bad day in the cockpit for reasons
far removed from a hard ground fault on your 6AWG
bus feeder . . . and THAT because you didn't conduct
due diligence in its installation.
Same thing applies to torque on your prop bolts,
replacing a tire that's flopping cordage, taking
an extra close look at forecasts during icing season,
and a host of things we do that go to reducing
risk.
In the case of the bus feeder, the risks are not
so much to the wire as to the thing the wire touches.
Case in point: C90 on short final experiences disconnect
of elevator cables. Pilot uses trim commands and power to
execute go-around, assesses the condition and successfully
lands the airplane with rudder, trim and power.
Pulling up floorboards in the cockpit revealed a 40A
protected feeder to the windshield de-ice inverter
had been mis-positioned against the elevator control
cable during a maintenance operation. Over what had to
be many hours of operation, motion of the cable wore
through the insulation bringing the cable into contact
with the hot wire. The arcing and sparking was of
insufficient intensity to come to attention of crew
in spite of the fact that it was going on virtually
under their feet.
The copper wire was barely damaged. The breaker never
popped while the elevator cable eventually eroded through
and parted. Compare thermal properties of copper versus
steel . . . this explains why the best steel safes have
intermediate layers of copper in their construction. It's
EASY to burn through steel . . . next to impossible on copper.
This narrative explains the high order probability that
even if you DID get your 6AWG feeder faulted to
ground, it's most likely to be a soft fault that
burns a hole in your airplane while doing little
damage to the wire . . . and certainly far short of
getting it to smoke and/or open a fuse/breaker.
Adding 'protection' to this pathway doubles the
number of joints in the pathway and adds nothing
demonstrable in terms of fault response . . . which
is why the spam-can builders don't do it either.
Bob . . .
http://www.matronics.com/Navigator?AeroElectric-Lista href="http://forums.matronics.com/" target="_blank">http://forums.mat====================
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