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Under Sized Wire

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Sun Aug 28, 2016 3:34 am Post subject: Under Sized Wire

On page 20 of the October 2016 issue of Kitplanes Magazine, the author wrote,  	  Quote: 	
		  "On one very nicely equipped RV-10, there was a 14 AWG wire being used as the main feed from the alternator.  It was not only improperly sized, but also a potential fire hazard, as it was attached to a 60-amp alternator breaker. Clearly, the wire would have melted before the breaker could have activated." 	
 I agree that the wire was very undersized and would get very hot.  But would it actually melt?

_________________
Joe Gores

racerjerry

Joined: 15 Dec 2009
Posts: 202
Location: Deer Park, NY

Posted: Sun Aug 28, 2016 4:05 am Post subject: Re: Under Sized Wire

The REAL problem is smoke in the cockpit, shortly followed by incapacitation.  Incapacitation happens long before the wire insulation turns to snot.



Aircraft wire MUCH BETTER - avoid auto parts store PVC insulated wire.



Use AC 43.13-1B as a guide and you will not go wrong.

Available here:

http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/99861

_________________
Jerry King

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sun Aug 28, 2016 7:07 am Post subject: Under Sized Wire

Not sure whether the builder ever saw Van's wiring diagram for the 

RV-10, and certainly could not have purchased the optional wiring kit. 

it uses AWG 8 aircraft wire for alternator to bus, and 8 AWG for starter 

relay to bus, so both battery feed and alternator feed to bus is 

appropriate. Master relay to starter relay is 2 AWG. My RV-10 runs about 

15 amps with everything in the panel plus strobes and nav lights, 

landing lights or pitot heat each add about 10 amps. Battery recharge 

after start will up the flow to a bit over 40 amps for a few minutes. 

Never have seen the current output of alternator get close to the rated 

60 amps. I suppose a night start with landing lights needed could get there.



On 8/28/2016 5:05 AM, racerjerry wrote:

 	  Quote: 	
		   



 The REAL problem is smoke in the cockpit, shortly followed by incapacitation.  Incapacitation happens long before the wire insulation turns to snot.



 Aircraft wire MUCH BETTER - avoid auto parts store PVC insulated wire.



 Use AC 43.13-1B as a guide and you will not go wrong.

 Available here:

 http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/99861



 --------

 Jerry King





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=459975#459975

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

rene(at)felker.com
Guest

Posted: Sun Aug 28, 2016 7:29 am Post subject: Under Sized Wire

Just FYI, after losing my first two alternators I upgraded to the Plane

Power 70 amp.  I left the 60amp breaker in the feed line.  Worked

fine....until I was on a long trip to FLA and it tripped the breaker.  Three

times......after take off and I think it was related to keying up the mic.

Also, it happened on the second leg of the day....hot day....engine heat

soaked.



I upgraded to a 70 AMP breaker.....all is fine.



My amp meter measures the flow to and from the main battery.  So no real

help there in determining if I was really seeing 70 amps.  My calculated max

load is nowhere near that....



Rene'

801-721-6080



--

ceengland7(at)gmail.com
Guest

Posted: Sun Aug 28, 2016 7:35 am Post subject: Under Sized Wire

Note that all context was lost in replying to an email that only 

included advice to avoid PVC insulated wire (which isn't really that big 

a deal; there's just better stuff available now).

On the subject of using 14awg wire on a 60 amp alternator: The point is 

not what is a typical draw; it's what the wire could potentially see. 

The mantra is: size the wire for the load (which can be a bit more than 

the *rated* capacity of the alternator, if the battery happened to be 

really low, or there were lots of loads like landing lights, pitot heat, 

etc), then fuse to protect the wire.

And none of us has answered the original question: Would the wire melt? 

I don't know the answer for sure, but I do recall the rule of thumb for 

fuseable links: make the link 4 wire sizes under the wire size you're 

protecting. Ex: a #12 fuseable link wire protects a #8 wire. So, if a #8 

is actually needed, #14 sounds like a quick blow fuse to me.

Charlie

On 8/28/2016 10:05 AM, Kelly McMullen wrote:

 	  Quote: 	

 <kellym(at)aviating.com>

 Not sure whether the builder ever saw Van's wiring diagram for the 

 RV-10, and certainly could not have purchased the optional wiring kit. 

 it uses AWG 8 aircraft wire for alternator to bus, and 8 AWG for 

 starter relay to bus, so both battery feed and alternator feed to bus 

 is appropriate. Master relay to starter relay is 2 AWG. My RV-10 runs 

 about 15 amps with everything in the panel plus strobes and nav 

 lights, landing lights or pitot heat each add about 10 amps. Battery 

 recharge after start will up the flow to a bit over 40 amps for a few 

 minutes. Never have seen the current output of alternator get close to 

 the rated 60 amps. I suppose a night start with landing lights needed 

 could get there.

 On 8/28/2016 5:05 AM, racerjerry wrote:

> 

> <gnking2(at)verizon.net>

>

> The REAL problem is smoke in the cockpit, shortly followed by 

> incapacitation.  Incapacitation happens long before the wire 

> insulation turns to snot.

>

> Aircraft wire MUCH BETTER - avoid auto parts store PVC insulated wire.

>

> Use AC 43.13-1B as a guide and you will not go wrong.

> Available here:

> http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/99861 

> --------

> Jerry King

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Aug 28, 2016 7:58 am Post subject: Under Sized Wire

At 06:34 AM 8/28/2016, you wrote:

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



 On page 20 of the October 2016 issue of Kitplanes Magazine, the author wrote, 

 > "On one very nicely equipped RV-10, there was a 14 AWG wire being used as the main feed from the alternator.  It was not only improperly sized, but also a potential fire hazard, as it was attached to a 60-amp alternator breaker. Clearly, the wire would have melted before the breaker could have activated."

  I agree that the wire was very undersized and would get very hot.  But would it actually melt? 	


   Interesting question. You may recall the experiment

   I conducted on a 20 AMP load through a 22AWG Tefzel

   wire on the workbench some years back. 



   While the wire did run hot (and voltage drop was

   no doubt higher than one would like) the jacket

   temperature stabilized well below maximum ratings for

   the insulation.



  http://tinyurl.com/6qr72fr



   I suspect a 14AWG hanging out in open

   air would not be seriously challenged for

   survival at 60A . . . but running the

   wire into bundles of other wires would

   have a profound influence on its

   ability to reject heat.



   Wire ratings are not so much a function

   of the copper but of the insulation,

   energy dissipated in the wire, temperature

   rise due to dissipation of that energy

   and ability to dump BTUs off into the

   environment. Insulation . . . and materials

   in contact with that insulation are the

   potential victims at risk.



 

   Bob . . .

argoldman(at)aol.com
Guest

Posted: Sun Aug 28, 2016 8:06 am Post subject: Under Sized Wire

Yes the wire will melt -or-not depending on its gauge and the amount of overload.

If my memory serves me correctly the fanles specify that a particular gauge will handle a particular amperage and with these variables will increase its temperature by so many degrees

The wire won't melt until the temperature gets to the melting point of copper or whatever material it is made of.      However the heat rise can cause all types of hurt as it starts to degrade the insulation and you get the characteristic electrical fire smell. 

Bundled wires have a smaller rating as the heat produced can effect adjacent wires

So with a slight overload the wires will

Probably not melt

A larger gauge will of course maintain more heat and possibly become a greater hazard 

Now add the situation of an undersized wire and a large current flow and it will indeed melt explosively-- or "fuse" which will Break the circuit. In fact thrall is what a fuse or fusable link is. The difference is that they are usually thermally protected and placed in a safe access able area

Rich

Sent from my iPhone

 	  Quote: 	
		   On Aug 28, 2016, at 10:37 AM, Charlie England <ceengland7(at)gmail.com> wrote:

 Note that all context was lost in replying to an email that only included advice to avoid PVC insulated wire (which isn't really that big a deal; there's just better stuff available now).

 On the subject of using 14awg wire on a 60 amp alternator: The point is not what is a typical draw; it's what the wire could potentially see. The mantra is: size the wire for the load (which can be a bit more than the *rated* capacity of the alternator, if the battery happened to be really low, or there were lots of loads like landing lights, pitot heat, etc), then fuse to protect the wire.

 And none of us has answered the original question: Would the wire melt? I don't know the answer for sure, but I do recall the rule of thumb for fuseable links: make the link 4 wire sizes under the wire size you're protecting. Ex: a #12 fuseable link wire protects a #8 wire. So, if a #8 is actually needed, #14 sounds like a quick blow fuse to me.

 Charlie

> On 8/28/2016 10:05 AM, Kelly McMullen wrote:

> 

> 

> Not sure whether the builder ever saw Van's wiring diagram for the RV-10, and certainly could not have purchased the optional wiring kit. it uses AWG 8 aircraft wire for alternator to bus, and 8 AWG for starter relay to bus, so both battery feed and alternator feed to bus is appropriate. Master relay to starter relay is 2 AWG. My RV-10 runs about 15 amps with everything in the panel plus strobes and nav lights, landing lights or pitot heat each add about 10 amps. Battery recharge after start will up the flow to a bit over 40 amps for a few minutes. Never have seen the current output of alternator get close to the rated 60 amps. I suppose a night start with landing lights needed could get there.

> 

>> On 8/28/2016 5:05 AM, racerjerry wrote:

>> 

>> 

>> The REAL problem is smoke in the cockpit, shortly followed by incapacitation.  Incapacitation happens long before the wire insulation turns to snot.

>> 

>> Aircraft wire MUCH BETTER - avoid auto parts store PVC insulated wire.

>> 

>> Use AC 43.13-1B as a guide and you will not go wrong.

>> Available here:

>> http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/99861 

>> 

>> --------

>> Jerry King

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sun Aug 28, 2016 1:11 pm Post subject: Under Sized Wire

I never saw the context with regard to PVC insulation. Not in the 

Kitplanes article,nor other messages here. The subject line was and is 

undersized wire. 14 AWG will carry 60 amps, especially if the run is 

short, for some period of time, probably not a long time. Question is 

whether the resistance generates more heat than the insulation can 

dissipate, and melts the insulation. Likely the load IS quite variable 

and steady state is no more than 80 percent of alternator capacity, more 

likely 30 percent.



On 8/28/2016 8:37 AM, Charlie England wrote:

 	  Quote: 	
		   

 <ceengland7(at)gmail.com>



 Note that all context was lost in replying to an email that only

 included advice to avoid PVC insulated wire (which isn't really that big

 a deal; there's just better stuff available now).

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Aug 28, 2016 5:37 pm Post subject: Under Sized Wire

At 10:28 AM 8/28/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Rene" <rene(at)felker.com>



 Just FYI, after losing my first two alternators I upgraded to the Plane

 Power 70 amp.  I left the 60amp breaker in the feed line.  Worked

 fine....until I was on a long trip to FLA and it tripped the breaker.  Three

 times......after take off and I think it was related to keying up the mic.

 Also, it happened on the second leg of the day....hot day....engine heat

 soaked.



 I upgraded to a 70 AMP breaker.....all is fine.



 My amp meter measures the flow to and from the main battery.  So no real

 help there in determining if I was really seeing 70 amps.  My calculated max

 load is nowhere near that.... 	


   This kinda has the 'smell' of a faulty

   breaker . . . what kind was it and do

   you still have it? 

 

   Bob . . .

rene(at)felker.com
Guest

Posted: Sun Aug 28, 2016 6:24 pm Post subject: Under Sized Wire

I might…..I will check at the hanger the next time I am out there.

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Robert L. Nuckolls, III

Sent: Sunday, August 28, 2016 7:35 PM

To: aeroelectric-list(at)matronics.com

Subject: RE: Re: Under Sized Wire

At 10:28 AM 8/28/2016, you wrote:

--> AeroElectric-List message posted by: "Rene" <rene(at)felker.com (rene(at)felker.com)>

Just FYI, after losing my first two alternators I upgraded to the Plane

Power 70 amp.  I left the 60amp breaker in the feed line.  Worked

fine....until I was on a long trip to FLA and it tripped the breaker.  Three

times......after take off and I think it was related to keying up the mic.

Also, it happened on the second leg of the day....hot day....engine heat

soaked.

I upgraded to a 70 AMP breaker.....all is fine.

My amp meter measures the flow to and from the main battery.  So no real

help there in determining if I was really seeing 70 amps.  My calculated max

load is nowhere near that....

  This kinda has the 'smell' of a faulty

  breaker . . . what kind was it and do

  you still have it? 

  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Aug 29, 2016 5:07 am Post subject: Under Sized Wire

At 09:20 PM 8/28/2016, you wrote:

  	  Quote: 	
		  I might…..I will check at the hanger the next time I am out there. 	


   Cool. 



 

 

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Tue Aug 30, 2016 5:48 am Post subject: Re: Under Sized Wire

In reference to my original question about 14 AWG wire melting at 60 amp, below are some links related to the subject.



Calculate the dissipated watts:

http://mustcalculate.com/electronics/wireproperties.php?mat=cu&l=1&area=2.08&areae=mm2&i=60&temp=20



All About Circuits forum discussion:

http://forum.allaboutcircuits.com/threads/how-to-calculate-heat-in-wires.108314/



WIRE AND CABLE MAXIMUM TEMPERATURE AND RISE IN AIR

DESIGN NOTE    November 1996, Updated September 2009

by  Douglas P. Arduini - Consultant

TABLE 3. MAXIMUM WIRE CURRENT FOR SINGLE COPPER WIRE IN FREE AIR

https://drive.google.com/open?id=0B7ZTG2VpCuDRR0VkRGpidG5DcTA

14 AWG at 43 amps = 125 degrees C temp rise

14 AWG at 47 amps =150 degrees C temp rise

14 AWG at 54 amps = 200 degrees C temp rise



Conclusion: 14 AWG wire would not melt at 60 amps

_________________
Joe Gores

rnjcurtis(at)charter.net
Guest

Posted: Tue Aug 30, 2016 10:10 am Post subject: Under Sized Wire

WIRE AND CABLE MAXIMUM TEMPERATURE AND RISE IN AIR

DESIGN NOTEÂ Â Â  November 1996, Updated September 2009

byÂ  Douglas P. Arduini - Consultant

TABLE 3. MAXIMUM WIRE CURRENT FOR SINGLE COPPER WIRE IN FREE AIR

https://drive.google.com/open?id=0B7ZTG2VpCuDRR0VkRGpidG5DcTA

14 AWG at 43 amps = 125 degrees C temp rise

14 AWG at 47 amps =150 degrees C temp rise

14 AWG at 54 amps = 200 degrees C temp rise

 

Conclusion: 14 AWG wire would not melt at 60 amps

 

Â Â Â Â Â Â Â Â Â Â Â Â Â  At 60 amps the temperature would be about 480 deg F!! 

Â Â Â Â Â Â Â Â Â Â Â Â Â  I would say that you would see some flowing of the wire 

Â Â Â Â Â Â Â Â Â Â Â Â Â  insulation and a bit of smoke.Â  Not what I would call an 

Â Â Â Â Â Â Â Â Â Â Â Â Â  ideal airborne situation!

 

Â Â Â Â Â Â Â Â Â Â Â Â Â  Roger

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