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user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Mon Jan 12, 2015 8:07 pm Post subject: UN-FUSED MAIN BUS FEEDER

It is common practice not to fuse the main bus feeder between the battery and the main power bus.  But what about aircraft with small electrical loads and small feeders?  For example, the RV-12 typically uses 10 to 15 amps total.  The main feeder is 12 awg per the factory plans.  This thread, http://www.vansairforce.com/community/showthread.php?t=120999

is about a fire (while on the ground) that was caused by the main feeder shorting out to the choke cable.  Do we need to rethink the practice of not fusing the main power feeder?  Or are good wiring practices safe enough?

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 12, 2015 9:30 pm Post subject: UN-FUSED MAIN BUS FEEDER

At 22:07 2015-01-12, you wrote:

 	  Quote: 	
		  



It is common practice not to fuse the main bus feeder between the 

battery and the main power bus.  But what about aircraft with small 

electrical loads and small feeders?  For example, the RV-12 

typically uses 10 to 15 amps total.  The main feeder is 12 awg per 

the factory plans.  This thread, 

http://www.vansairforce.com/community/showthread.php?t=120999

is about a fire (while on the ground) that was caused by the main 

feeder shorting out to the choke cable.  Do we need to rethink the 

practice of not fusing the main power feeder?  Or are good wiring 

practices safe enough?

Joe


	


   The FARS speak to the risks for ENGINE CRANKING

   feeders where bus feeders are on the same order

   of risk as the cranking circuits.



   Airplanes that are powered with 'tiny' alternators

   tend to have bus feeders to match and are

   at greater risk from battery-fed faults. The

   thread is extensive and riddled with unclear

   and/or erroneous words. I'll need to digest

   it a bit . . .



   The short answer is that some form of transient

   tolerant fault protection wouldn't hurt but better

   installation of the potentially vulnerable wire

   would be better. So yes, good wiring practices

   are the first line of defense against such events.



   The fact that this wire became mechanically

   compromised speaks to questionable shop practice.

   I'll sift through the narrative and report back.



   Watch this space.



   Bob . . .

jluckey(at)pacbell.net
Guest

Posted: Mon Jan 12, 2015 9:46 pm Post subject: UN-FUSED MAIN BUS FEEDER

Joe,



Thanks for bringing this to our attention.  Very scary and very interesting.  A poster on the VansAirforce forum states that the RV-12 is "certified" under an ASTM standard.



I found this:

ASTM F2245 - 14. Standard Specification for Design and Performance of a Light Sport Airplane. http://www.astm.org/Standards/F2245.htm

The abstract for that document suggests that it discusses electrical systems.  I would like to get a look at that document but I'm hesitant to spend $60 just for a look-see.



Does anyone have a copy of that document that I could look at?  Has anyone on this forum seen/read that document and would care to comment on it.





Back to the VansAirforce post - The original poster did not post any  pictures of the before & after.  That's a shame because it might be very instructive if we could see how that feeder was routed.

-Jeff

PS - As long-time members of this forum may recall, I have been a proponent of protecting all feeders and my designs incorporate such protection. This current (no pun intended) issue is a good example of why.  If this fire had occurred while airborne the results could have been catastrophic.



 

     On Monday, January 12, 2015 8:24 PM, user9253 <fransew(at)gmail.com> wrote:  

   --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>It is common practice not to fuse the main bus feeder between the battery and the main power bus.  But what about aircraft with small electrical loads and small feeders?  For example, the RV-12 typically uses 10 to 15 amps total.  The main feeder is 12 awg per the factory plans.  This thread, http://www.vansairforce.com/community/showthread.php?t=120999is about a fire (while on the ground) that was caused by the main feeder shorting out to the choke cable.  Do we need to rethink the practice of not fusing the main power feeder?  Or are good wiring practices safe enough?Joe--------Joe GoresRead this topic online here:http://forums.matronics.com/viewtopic.php?p=436938#436938

  

 

  

 

 [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 13, 2015 4:09 am Post subject: UN-FUSED MAIN BUS FEEDER

At 23:45 2015-01-12, you wrote:

  	  Quote: 	
		  Joe,



 Thanks for bringing this to our attention.  Very scary and very interesting.  A poster on the VansAirforce forum states that the RV-12 is "certified" under an ASTM standard.



 I found this:

 ASTM F2245 - 14. Standard Specification for Design and Performance of a Light Sport Airplane.  http://www.astm.org/Standards/F2245.htm



 The abstract for that document suggests that it discusses electrical systems.  I would like to get a look at that document but I'm hesitant to spend $60 just for a look-see.



 Does anyone have a copy of that document that I could look at?  Has anyone on this forum seen/read that document and would care to comment on it.



 

 Back to the VansAirforce post - The original poster did not post any pictures of the before & after.  That's a shame because it might be very instructive if we could see how that feeder was routed.



 -Jeff



 PS - As long-time members of this forum may recall, I have been a proponent of protecting all feeders and my designs incorporate such protection. This current (no pun intended) issue is a good example of why.  If this fire had occurred while airborne the results could have been catastrophic. 	




    Yes, there are a constellation of risks associated

    with materials and processes for assembling

    airplanes. I recall a couple of instances

    of fuel fed fires on Glasairs waaayyy back when

    with root cause traced to poorly installed

    fire wall fittings on fuel lines. An RV8

    went down in flames with the pilot electing

    to do a no-parachute egress from the aircraft.

    Root cause for this unhappy event will never be

    known . . . but a whole lot of history and FMEA

    practices can give us some good ideas . . . and

    I'll bet none of them are mitigated by ADDING

    another feature to a proven system. It's more

    likely that some simple failure to observe

    good practice is the root cause. Missing safety

    wire, o-ring pinched, cracked line, etc. etc.



    Hard Reality of Life: No amount of ISO9000

    documentation and holy-watered work instructions

    will guarantee that one of life's little

    "Aw S(at)#$s" won't jump up an bite you.



    Are you working under the assumption that the

    triggering event was a hard faulted 12AWG bus

    feeder?



    In your hypothesis, how does a relatively young,

    robust wire get compromised severely over

    a short period of time to produce such

    a high energy event?



    I'm going to sift through the narrative but

    there was one poster to the thread that wondered

    about engine grounding. Those control cables

    (wound jacket Bowden controls?) are steel and

    relatively poor conductors. If the airplane's

    engine were not properly bonded to a high integrity

    ground system, then the current demands of an engine

    start circulating in the control cables offers

    a plausible explanation for the energy flows

    that triggered the event.



    Before we chase the rabbit down the bus-feeder-

    protection hole, let's assure ourselves that

    it was a hard-faulted WIRE that started the unhappy

    event and not a couple of heater-coil control

    cables being tasked to do things never intended

    by the designers. I am skeptical that a burning

    12AWG wire bundled with steel engine controls would

    do much damage to them. On the other hand, engine

    controls masquerading as crankcase grounds would

    not only exhibit severe heat stress, they would

    compromise the insulation on wires bundled together

    the controls.



    I looked at the link for the ATSM document . . .

    33 pages for $60 ????  I'm pretty sure Textron

    has a subscription to such documents, I'll see

    if I can put my hands on one. But at best, it's

    an index to a bunch of other documents or at

    worst, a gathering of lofty words speaking

    to design goals dreamed up by individuals with

    little or no experience at the craft.



    If you look through the z-figures, you'll see

    fusible links at the source end of bus feeders

    on 'tiny alternator' airplanes. Airplanes with

    big alternators are assumed to carry the same

    gage wire throughout the cranking circuit and

    bus feeders . . . 4AWG or larger. Probability

    of hard faulting a fat wire in a manner that

    puts the wire at risk is exceedingly low as

    demonstrated in hundreds of thousands of examples

    over the last century of aviation history.



    The fact that the 12AWG wire in question burned

    only ahead of the fire wall suggests that it

    came to ground at the fire wall penetration

    site. How would/did this happen? Just

    for grins . . . connect a 12AWG wire to a

    battery grounded to a 'fire wall', run the

    wire through a hole in that piece of metal

    then work the wire against the edge of the hole

    until you produce a fault sufficient to

    burn the wire.  How much time? How much force?

    What kind of motion? What was going on from

    the time sparks first started to fly (soft

    fault) until connection could be made to

    cook the wire? Now, how did this happen in

    the event airplane?



    The discussion I downloaded last night is

    long on supposition and conjecture . . . short

    on failure analysis. It seems more likely that the

    controls got hot first and compromised the

    insulation which triggered an electrical

    compromise of the wire but without sifting

    the aftermath in a logical and ordered manner,

    the facts are elusive.



    We need to be sure of the simple-ideas in

    physics and proven practices before painting

    this event as a justification for pasting

    a band-aid on a system that was bleeding

    profusely somewhere else.



 

   Bob . . .    [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Tue Jan 13, 2015 4:05 pm Post subject: Re: UN-FUSED MAIN BUS FEEDER

 	  Quote: 	
		  Are you working under the assumption that the 

triggering event was a hard faulted 12AWG bus 

feeder? 	


Yes, that is what happened, in my opinion, after reading the builder's description in this post: http://www.vansairforce.com/community/showpost.php?p=945235&postcount=17

Posts by others in that thread are only speculation.

 	  Quote: 	
		  In your hypothesis, how does a relatively young, 

robust wire get compromised severely over 

a short period of time to produce such 

a high energy event? 	


The #12 awg wire that burned is the main feeder between the contactor and the instrument panel.  The wire does NOT run parallel to or with choke or throttle cables through the firewall.  Wires in the RV-12 pass through a separate hole in the firewall.  The #12 wire runs perpendicular to and under the throttle cables.  In my RV-12, there is a half inch space between the #12 wire and throttle cables and both are held apart by cushion clamps.  In the accident RV-12, the #12 wire must have been in contact with the underside of a throttle cable.  I suspect that the insulation on the wire was abraded by a vibrating throttle cable.  The copper wire then welded itself to the steel cable.  The builder is adamant that his engine is well grounded and thus had nothing to do with the incident.  The Rotax engine starts so quickly, within 1 or 2 seconds, that it seems unlikely that throttle and choke cables would have time to heat up over their entire length to a temperature high enough to melt wire insulation.  The Rotax dynamo does not use engine ground for conducting current as would a conventional alternator.  The single phase AC output of the dynamo is conducted through two wires to the rectifier/regulator which is mounted on the firewall.  After engine start, only engine-instrument-sensor current is dependent on the engine ground.  Without having the fire damage to examine, all we have to go by is the post by the pilot-builder. Below is a link to a picture of the wire in question in my airplane, not the accident aircraft.  http://tinyurl.com/RV-12-wires

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 13, 2015 6:12 pm Post subject: UN-FUSED MAIN BUS FEEDER

The #12 awg wire that burned is the main feeder between the contactor and the instrument panel.  The wire does NOT run parallel to or with choke or throttle cables through the firewall.  Wires in the RV-12 pass through a separate hole in the firewall.  The #12 wire runs perpendicular to and under the throttle cables.  In my RV-12, there is a half inch space between the #12 wire and throttle cables and both are held apart by cushion clamps.  In the accident RV-12, the #12 wire must have been in contact with the underside of a throttle cable.  I suspect that the insulation on the wire was abraded by a vibrating throttle cable.  The copper wire then welded itself to the steel cable.  The builder is adamant that his engine is well grounded and thus had nothing to do with the incident.  The Rotax engine starts so quickly, within 1 or 2 seconds, that it seems unlikely that throttle and choke cables would have time to heat up over their entire length to a temperature high enough to melt wire insulation.  The Rotax dynamo does not use engine ground for conducting current as would a conventional alternator.  The single phase AC output of the dynamo is conducted through two wires to the rectifier/regulator which is mounted on the firewall.  After engine start, only engine-instrument-sensor current is dependent on the engine ground.  Without having the fire damage to examine, all we have to go by is the post by the pilot-builder. Below is a link to a picture of the wire in question in my airplane, not the accident aircraft.   http://tinyurl.com/RV-12-wires

 Joe



     Aha! Good data points. Just got a task mailed off to   a customer and had time to read the thread downloaded   last night.

 

    It seems clear that the wire insulation was compromised   against the control cables . . . failure to observe   common practice for the maintenance of spacing.

 



    Picked this out of the downloaded thread . . .



 On the issue of a fusible link, it is not true that it would create a weak spot electrically. A fusible link will not fail in the event of a spurious spike in current; only in the event of a major, uncontrolled power draw....a short circuit. It is true that it is 4 wire sizes smaller ( or 4 numbers larger); 16 awg in the case of the RV-12 battery power wire. Regarding the philosophy of aircraft design, to wit; the issue of a system failure versus a fire aloft is hardly worth discussion. Seriously? In a VFR, daytime-only RV-12, we'd consider a fire aloft a better deal than a display failure?! I appreciate all the redundant advice to carefully route & shield the battery power wire. Great advice. Took care of it. But that is a separate issue of the wire becoming shorted for whatever unforeseen reason. And there seems to be much naive comment on this blog that if there's a problem, a fuse would blow. It needs to be clearly understood here that if a power wire shorts out in the RV-12, a fantastically dangerous hot spot will result; in essence, an arc welder. That's what I had, and the damage was devastating. Additionally, it needs to be understood that proper engine-to-fuselage grounding will not protect against such a short circuit. My engine is properly grounded, In fact, I long ago took the precaution of an additional ( and very substantial) electrical ground wire. Unprotected +12v current will find ANY path when it "shorts" out. In my case, it virtually welded right through both the throttle & choke cables, as well as destroying the #22 (black) ground wire in the GPS antenna/receiver cable all the way to the connector on the Vans AV-5000A control module in the avionics bay (a $600 piece)



 

   As I mentioned last night, as wire sizes drop out

   of the relatively invincible 'fat wire' category,

   they do become vulnerable a hard-fault burn. The

   fusible link is one way to go. It's compact, inexpensive

   and effective. Cars have used them for years but 

   to my knowledge, the TC aircraft industry has never

   embraced them. There's a class of circuit protector

   with LONG fusing constants commonly referred to as

   a current limiter. The ANL series devices . . .



 

  http://tinyurl.com/k9tmfmh



 

   . . . have been a common ingredient in time-delay,

   hard-fault protection for over 70 years. The

   automotive industry has used a variety of

   heavy-fuses as well. An interesting line

   that popped up 30 or so years ago was the

   miniature current limiters or MANL series

   devices. They're popular with installers

   of kilowatt boom boxes in automobiles. They're

   readily available from hundreds of sources.



 

  http://tinyurl.com/pcuscp2



 

   I've not seen a MANL holder from the automotive

   world that instilled much confidence. Not sure

   about the base materials but they're probably

   okay. If it were my installation, I'd make base

   our of a piece of phenolic or Delrin . . .but

   the current limiters are just fine,



   Fusible link wire is available in bulk from

   a host of automotive supply houses. Here's

   one such product

 

  http://tinyurl.com/p3hrq22



   

   The fusible link is mechanically attractive.

   Installs with splices, ties right into a wire

   bundle with the rest of the wires. If it's in

   a bundle, it would e a good thing to add a layer

   of silicon impregnated fiberglas sleeving like

   that described in my articles and offered in

   B&C's fusible link kit.



 

   In any case, protecting light feeders

   directly attached to a battery is a good idea.



 

   Bob . . .    [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Tue Jan 13, 2015 7:12 pm Post subject: Re: UN-FUSED MAIN BUS FEEDER

Thanks for your insight, Bob.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 14, 2015 8:21 am Post subject: UN-FUSED MAIN BUS FEEDER

 	  Quote: 	
		  

   In any case, protecting light feeders

   directly attached to a battery is a good idea. 	


    P.S. Keep in mind that there are numerous ways

    a failure can take down the main bus. Battery

    contactor failure. Failure in controls for

    battery contactor . . . as well as any fault

    that compromises the main bus feeder.



    This is one reason why the e-bus evolved to

    the present day. It's a two-feed bus

    that not only offers easily accessed, planed

    reduction in load. It also offers redundancy

    in source paths that negates risks for loss

    of main bus.



 

   Bob . . .    [quote][b]

jluckey(at)pacbell.net
Guest

Posted: Wed Jan 14, 2015 9:07 am Post subject: UN-FUSED MAIN BUS FEEDER

Bob,



Were you able to gain access to an ASTM subscription.  I would like to get a look at the  http://www.astm.org/Standards/F2245.htm document.

-Jeff

      On Wednesday, January 14, 2015 8:32 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:  

      	  Quote: 	
		     In any case, protecting light feeders   directly attached to a battery is a good idea. 	
    P.S. Keep in mind that there are numerous ways    a failure can take down the main bus. Battery    contactor failure. Failure in controls for    battery contactor . . . as well as any fault    that compromises the main bus feeder.    This is one reason why the e-bus evolved to    the present day. It's a two-feed bus    that not only offers easily accessed, planed    reduction in load. It also offers redundancy    in source paths that negates risks for loss    of main bus.     Bob . . .    

 	  Quote: 	
		  

	


  

 

  



 



 [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 14, 2015 1:23 pm Post subject: UN-FUSED MAIN BUS FEEDER

At 11:06 2015-01-14, you wrote:

  	  Quote: 	
		  Bob,



 Were you able to gain access to an ASTM subscription.  I would like to get a look at the  http://www.astm.org/Standards/F2245.htm document. 	


   Yeah, got a peek at the full document . . . what

   is said is rather well written. 33 pages doesn't

   cover much from a systems perspective (like part 23)

   but they do get into details on weights, handling

   qualities and performance. Here's excerpts that

   speak to electrical systems  . . . 



 ======

 Under "Required Equipment"

 --------------------------------

 A2.6.5 An adequate source of electrical energy for all

 installed electrical and radio equipment specified in A2.9.2;



 



 =====================

 8.4 Miscellaneous Equipment—Other Than EPU:

 ----------------------------------------------

 8.4.1 If installed, an electrical system shall include a master

 switch and overload protection devices (fuses or circuit breakers).



 8.4.2 The electric wiring shall be sized according to the load

 of each circuit.



 8.4.3 The battery installation shall withstand all applicable

 inertia loads.



 8.4.4 Battery containers shall be vented outside of the

 airplane (see 6.5).



 ======================

 A2.9 Electrical Requirements

 -----------------------------------------------

 A2.9.1 Switches—Each switch must be:



 A2.9.1.1 Rated by the switch manufacturer to carry its

 circuit’s current;



 A2.9.1.2 For circuits containing incandescent lamps, have a

 minimum in-rush rating of 15 times the lamp’s continuous

 current;



 A2.9.1.3 Constructed with enough distance or insulating

 material between current carrying parts and the housing so that

 vibration in flight will not cause shorting;



 A2.9.1.4 Accessible to the pilot;



 A2.9.1.5 Labeled as to operation and the circuit controlled;

 and



 A2.9.1.6 Illuminated in accordance with A2.7.1.



 A2.9.2 Circuit Protection Requirements—Circuit overload

 protection (fuses or circuit breakers) must:



 A2.9.2.1 Be installed on each circuit containing wiring,

 equipment, or other components rated for less than the maximum

 output of the battery and alternator or generator;



 A2.9.2.2 Be appropriately rated for each component installed

 on the protected circuit;



 A2.9.2.3 Be accessible to and in clear view of the pilot;



 A2.9.2.4 Open before the conductor emits smoke; and



 A2.9.2.5 Automatic re-set circuit breakers may not be used.



 A2.9.3 Electrical Energy Requirements—The total continuous

 electrical load may not exceed 80 % of the total rated

 generator or alternator output capacity.



 A2.9.4 Conductor Requirements—Any wire or other material

 intended to conduct electricity must be:



 A2.9.4.1 Rated to carry its circuits current;



 A2.9.4.2 For wiring rated to 150°C, 600 V minimum;



 A2.9.4.3 Constructed with enough distance or insulating

 material between current carrying conductors so that vibration

 in flight will not cause shorting; and



 A2.9.4.4 Where used, insulating material must have, at a

 minimum, the equivalent or better properties of either PTFE

 -polytetrafluoroethylene (commonly known by the trade name,

 TEFLON) or ETFE-(Frequently referred to by the trade name,

 TEFZEL) a copolymer of PTFE and of polyethylene including:



 (1) Temperature,



 (2) Abrasion resistance,



 (3) Cut-through resistance,



 (4) Chemical resistance,



 (5) Flammability,



 (6) Smoke generation,



 (7) Flexibility,



 ( Creep (at temperature), and



 (9) Arc propagation resistance.



 ============



 All pretty much common sense stuff . . . 



 

   Bob . . .    [quote][b]

peter(at)sportingaero.com
Guest

Posted: Wed Jan 14, 2015 1:56 pm Post subject: UN-FUSED MAIN BUS FEEDER

Does the para below mean that VPX type equipment is not permitted?



Peter



On 14/01/2015 21:22, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   A2.9.2.5 Automatic re-set circuit breakers may not be used.

jluckey(at)pacbell.net
Guest

Posted: Wed Jan 14, 2015 2:06 pm Post subject: UN-FUSED MAIN BUS FEEDER

Bob,

Thanks for that.  A poster on VansAirforce remarked that putting an overload protection device in the feeder to the distribution panel (the wire in question) was specifically prohibited in the ASTM 2245. (which I find hard to believe.)

Did you see any language to that effect?

Thank,

-Jeff

 

     On Wednesday, January 14, 2015 1:33 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

  

  



   At 11:06 2015-01-14, you wrote:

  	  Quote: 	
		  Bob,



 Were you able to gain access to an ASTM subscription.  I would like to get a look at the  http://www.astm.org/Standards/F2245.htm document. 	


   Yeah, got a peek at the full document . . . what

   is said is rather well written. 33 pages doesn't

   cover much from a systems perspective (like part 23)

   but they do get into details on weights, handling

   qualities and performance. Here's excerpts that

   speak to electrical systems  . . . 



 ======

 Under "Required Equipment"

 --------------------------------

 A2.6.5 An adequate source of electrical energy for all

 installed electrical and radio equipment specified in A2.9.2;



 



 =====================

 8.4 Miscellaneous Equipmentâ€”Other Than EPU:

 ----------------------------------------------

 8.4.1 If installed, an electrical system shall include a master

 switch and overload protection devices (fuses or circuit breakers).



 8.4.2 The electric wiring shall be sized according to the load

 of each circuit.



 8.4.3 The battery installation shall withstand all applicable

 inertia loads.



 8.4.4 Battery containers shall be vented outside of the

 airplane (see 6.5).



 ======================

 A2.9 Electrical Requirements

 -----------------------------------------------

 A2.9.1 Switchesâ€”Each switch must be:



 A2.9.1.1 Rated by the switch manufacturer to carry its

 circuitâ€™s current;



 A2.9.1.2 For circuits containing incandescent lamps, have a

 minimum in-rush rating of 15 times the lampâ€™s continuous

 current;



 A2.9.1.3 Constructed with enough distance or insulating

 material between current carrying parts and the housing so that

 vibration in flight will not cause shorting;



 A2.9.1.4 Accessible to the pilot;



 A2.9.1.5 Labeled as to operation and the circuit controlled;

 and



 A2.9.1.6 Illuminated in accordance with A2.7.1.



 A2.9.2 Circuit Protection Requirementsâ€”Circuit overload

 protection (fuses or circuit breakers) must:



 A2.9.2.1 Be installed on each circuit containing wiring,

 equipment, or other components rated for less than the maximum

 output of the battery and alternator or generator;



 A2.9.2.2 Be appropriately rated for each component installed

 on the protected circuit;



 A2.9.2.3 Be accessible to and in clear view of the pilot;



 A2.9.2.4 Open before the conductor emits smoke; and



 A2.9.2.5 Automatic re-set circuit breakers may not be used.



 A2.9.3 Electrical Energy Requirementsâ€”The total continuous

 electrical load may not exceed 80 % of the total rated

 generator or alternator output capacity.



 A2.9.4 Conductor Requirementsâ€”Any wire or other material

 intended to conduct electricity must be:



 A2.9.4.1 Rated to carry its circuits current;



 A2.9.4.2 For wiring rated to 150Â°C, 600 V minimum;



 A2.9.4.3 Constructed with enough distance or insulating

 material between current carrying conductors so that vibration

 in flight will not cause shorting; and



 A2.9.4.4 Where used, insulating material must have, at a

 minimum, the equivalent or better properties of either PTFE

 -polytetrafluoroethylene (commonly known by the trade name,

 TEFLON) or ETFE-(Frequently referred to by the trade name,

 TEFZEL) a copolymer of PTFE and of polyethylene including:



 (1) Temperature,



 (2) Abrasion resistance,



 (3) Cut-through resistance,



 (4) Chemical resistance,



 (5) Flammability,



 (6) Smoke generation,



 (7) Flexibility,



 ( Creep (at temperature), and



 (9) Arc propagation resistance.



 ============



 All pretty much common sense stuff . . . 



     Bob . . .    

[quote]wwwlow" target="_blank" href="http://www.buildersbooks.com/">www.buildersb=     * My Pilot Store http://www.matronics.com/Nav========================

" target="_blank" href="http://forums.matronics.com/">http://forums.mat===================


[b]

jluckey(at)pacbell.net
Guest

Posted: Wed Jan 14, 2015 2:17 pm Post subject: UN-FUSED MAIN BUS FEEDER

Oops!  My paraphrasing was inaccurate.  Here is what the other poster said:



"The ASTM specs that the RV-12 is certificated under specifically  prohibit the use of of a circuit protector that is not resetable by the  pilot.  That means the wire highlighted in this discussion can not have a  fusible link or any other circuit protection that would actually be  capable of preventing a failure in the location that this one was."





Bob, In reading the text you supplied, I did not see anything that supports the above statement.  Is there more to the ASTM doc that supports the above?

I'm simply trying to understand what the "Standards" ACTUALLY say. Therefore I'm trying to filter-out hearsay, mis-interpretation, urban legend, & wive's tales.



Again, thanks,

-Jeff



 

     On [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Wed Jan 14, 2015 2:27 pm Post subject: Re: UN-FUSED MAIN BUS FEEDER

A2.9.2 Does not specifically mention fusible links.  Are they considered fuses that must (A2.9.2.3) be accessible to and in clear view of the pilot?

What if a #12 AWG main power feeder were replaced with 8 AWG except for a short section of 12 AWG enclosed in a fire sleeve?  Would that meet the letter of the law?  Sometimes rules and regulations prohibit using common sense.

Joe

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 14, 2015 3:01 pm Post subject: UN-FUSED MAIN BUS FEEDER

At 16:05 2015-01-14, you wrote:

  	  Quote: 	
		  Bob,



 Thanks for that.  A poster on VansAirforce remarked that putting an overload protection device in the feeder to the distribution panel (the wire in question) was specifically prohibited in the ASTM 2245. (which I find hard to believe.)



 Did you see any language to that effect?



 Thank,



 -Jeff 	


   Nope . . . in fact, there were words that spoke

   specifically to:



 A2.9.2.1 Be installed on each circuit containing wiring,

 equipment, or other components rated for less than the maximum

 output of the battery and alternator or generator;



   While poorly worded, I think the intent is similar

   to the reasoning for not protecting fat wires

   in legacy aircraft.



   Reading between the lines, it says that any wire

   subject to catastrophic stresses from engine driven

   power or battery should be protected. But the

   phrase "maximum output of the battery" is

   curious . . . most SLVA batteries of any size

   are good for 500-1200A in a faulted condition.



   Is that the battery's 'rating'?  If so, then

   one might want to consider fusing a 4AWG

   cranking feeder . . . I think I like the FAR23

   wording better.



   The wording also speaks to equipment and other

   components. Do the writers now expect circuit

   protection at the bus to look out for potential

   faults within a piece of equipment? And where

   would the system integrator find data that speaks

   to a fault current limit for any failure within

   a device?



   It would be interesting to know why the wording

   in Parts 23 and 25 were inadequate to the new

   order . . .



   But in any case, I too believe the poster

   was in error.



 

 

   Bob . . .    [quote][b]

kenryan

Joined: 20 Oct 2009
Posts: 424

Posted: Wed Jan 14, 2015 3:47 pm Post subject: UN-FUSED MAIN BUS FEEDER

I keep asking myself why I would use a fusible link instead of an inline fuse. So far I am simply not convinced. On Jan 14, 2015 5:33 PM, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:[quote]--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 A2.9.2 Does not specifically mention fusible links.Â  Are they considered fuses that must (A2.9.2.3) be accessible to and in clear view of the pilot?

 What if a #12 AWG main power feeder were replaced with 8 AWG except for a short section of 12 AWG enclosed in a fire sleeve?Â  Would that meet the letter of the law?Â  Sometimes rules and regulations prohibit using common sense.

 Joe

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=437014#437014

 

 

 

 

 

 

 

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 [b]

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Wed Jan 14, 2015 4:29 pm Post subject: Re: UN-FUSED MAIN BUS FEEDER

 	  Quote: 	
		  I keep asking myself why I would use a fusible link instead of an inline fuse. 	


I think that fusible links are more robust and less likely to fail than a fuse.  However, there are some very robust types of fuses like the ANL.  The old style automotive glass fuses were prone to fail because the fuse holders did not make a high pressure contact.  Yeah, if I wanted to protect my 12 AWG main feeder from vaporizing, I would install an inline 30 amp ATC fuse.  My posting about fusible links was in response to a Van's Aircraft employee who stated that fusible links in the engine compartment were prohibited by ASTM rules.  But it seems those rules are ambiguous and open to interpretation.

Joe

_________________
Joe Gores

jluckey(at)pacbell.net
Guest

Posted: Wed Jan 14, 2015 5:20 pm Post subject: UN-FUSED MAIN BUS FEEDER

Ken,

Regarding a fusible link - There is one reason I can think of that  someone might choose a fusible like:  Fusible Links are a "slow-blow" kind of animal where a standard fuse is not.  If the mission requires a slow-blow device then the Fusible Link might be the right choice.  Fusible Links are also cheap.



But I'm with you, my preference is to use Current Limiters like ANL or Littlefuse MIDIs instead of a Fusible Link.  But these fuses must be mounted on something...

-Jeff

 

     On Wednesday, January 14, 2015 3:57 PM, Ken Ryan <keninalaska(at)gmail.com> wrote:

  

  



 I keep asking myself why I would use a fusible link instead of an inline fuse. So far I am simply not convinced.

 On Jan 14, 2015 5:33 PM, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:

[quote]--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

 

 A2.9.2 Does not specifically mention fusible links.  Are they considered fuses that must (A2.9.2.3) be accessible to and in clear view of the pilot?

 What if a #12 AWG main power feeder were replaced with 8 AWG except for a short section of 12 AWG enclosed in a fire sleeve?  Would that meet the letter of the law?  Sometimes rules and regulations prohibit using common sense.

 Joe

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=437014#437014

 

 

 

 

 

 

 

 ===========

 br> fts!)

 r> > com" target="_blank">www.aeroelectric.com

 w.buildersbooks.com" target="_blank">www.buildersbooks.com

 p.com" target="_blank">www.homebuilthelp.com

 e.com" target="_blank">www.mypilotstore.com

 " target="_blank">www.mrrace.com

 target="_blank">http://www.matronics.com/contribution

           -Matt Dralle, List Admin.

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 Electric-List" target="_blank">http://www.matronics.com/Navigator?AeroElectric-List

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[b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 14, 2015 5:55 pm Post subject: UN-FUSED MAIN BUS FEEDER

At 17:46 2015-01-14, you wrote:



  	  Quote: 	
		  I keep asking myself why I would use a fusible link instead of an inline fuse. So far I am simply not convinced.

 On Jan 14, 2015 5:33 PM, "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)> wrote: 	




   If a FUSE  . . . meaning NOT an ANL current limiter,

   then pick a fuse that is 2 to 3x larger than the

   operational current rating for the wire. I.e. a 12AWG

   wire (20A) would want a 60A fuse. This is because fuses

   are normally applied in situations where relatively

   fast response is desirable . . . not so for feeder

   protection.



   ANL style devices and fusible links have very LONG

   time constants. No nuisance trips of these puppies.

   Yet, they will operate to put a box around the 

   protection event whether inside the housing of

   a limiter or under the jacket of a fusible link.



   Mechanically, the fusible link is attractive because

   it generally looks like and can be treated almost

   like wire. Crimped joints on each end. Any other

   device is 'lumpy', puts more connections in the

   pathway and may need to be mounted to some mechanically

   immobile surface.



 

   Bob . . .    [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 14, 2015 6:16 pm Post subject: UN-FUSED MAIN BUS FEEDER

At 16:17 2015-01-14, you wrote:

 	  Quote: 	
		  Oops!  My paraphrasing was inaccurate.  Here is what the other poster said:



"The ASTM specs that the RV-12 is certificated under specifically 

prohibit the use of of a circuit protector that is not resetable by the pilot.


	


    Opps . . . yeah, that makes a difference. Can't imagine

    why that assertion is part of the spec . . . there's

    no foundation in FMEA for the outcome of any given

    flight by fiddling with circuit protection in the air.



 	  Quote: 	
		  That means the wire highlighted in this discussion can not have a 

fusible link or any other circuit protection that would actually be 

capable of preventing a failure in the location that this one was."


	


   My argument would be that the fusible link or ANL

   at the battery contactor is not unlike similar devices

   scattered about the airplane on King Airs and

   their hot-air cousins . . . and those cannot be reached

   by pilots either. Lots of breakers on those airplanes

   can't be reached either.  These are not systems fuses, they're

   a hedge against catastrophic events that either (1) put

   every device on that feeder at risk of going dark or (2) the

   whole damned airplane at risk of going down very brightly.



   I'd let the enforcer of requirements choose . . .

 	  Quote: 	
		  Bob, In reading the text you supplied, I did not see anything that 

supports the above statement.  Is there more to the ASTM doc that 

supports the above?



I'm simply trying to understand what the "Standards" ACTUALLY say. 

Therefore I'm trying to filter-out hearsay, mis-interpretation, 

urban legend, & wive's tales.


	


   Understand . . . I think I expressed some misgivings

   about the relative goodness of this new 'spec'.

   Gee, only 33 pages long, a few years old . . . bet the

   guys sitting around the table on this one never

   did an FMEA or turned wrenches on airplanes.



   Consider AC43-13 . . . DECADES old and sifted by

   dozens of high-powered spec writers over the years.

   However, when offered to EAA for 'friendly critical review'

   release of a major revision was delayed another 18 months

   and it was STILL full of holes.



   Color this ol' dog skeptical as an outcome of having

   watched decades of this stuff run under the bridge.

   If it were my airplane, there would be a fusible link

   at the battery contactor . . . hidden under the sleeving.

   Nobody but me needs to know its there. What does Van's

   factory wiring dictate?

   Bob . . .

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