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Surplus Wire

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BMC_Dave

Joined: 04 Jul 2018
Posts: 40

Posted: Sat Jun 13, 2020 5:22 pm Post subject: Surplus Wire

I have a bunch of surplus BMS13-48 ETFE wire, 5 nickle-plated 24ga conductors, shielded.



Reading the AEC it seems an ok practice to bundle these conductors for larger currents, so I could use them together as a 18ga substitute from the table in Figure 8-3.



I'm wondering what I should do with the shield though? Is it useful to connect it to anything?



Any other advice/cautions about using nickle-plated BMS? My work let me dig through the scrap bin and I have hundreds of feet of this stuff. Thanks.

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ceengland7(at)gmail.com
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Posted: Sat Jun 13, 2020 6:37 pm Post subject: Surplus Wire

On 6/13/2020 8:22 PM, BMC_Dave wrote:

 	  Quote: 	
		   



 I have a bunch of surplus BMS13-48 ETFE wire, 5 nickle-plated 24ga conductors, shielded.



 Reading the AEC it seems an ok practice to bundle these conductors for larger currents, so I could use them together as a 18ga substitute from the table in Figure 8-3.



 I'm wondering what I should do with the shield though? Is it useful to connect it to anything?



 Any other advice/cautions about using nickle-plated BMS? My work let me dig through the scrap bin and I have hundreds of feet of this stuff. Thanks.

I might be speaking out of the wrong orifice, but IIRC, nickel plated is 
	


intended only for crimping, and is not solder friendly. If you're only 

crimping, should be good to go. Just quite a bit of extra weight for the 

equivalent wire gauge.



Have you thought about selling it off to other builders, to use for 

intercom wiring, trim servos, etc, and using the money to purchase 

appropriate gauges for various devices?



Charlie



-- 

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BMC_Dave

Joined: 04 Jul 2018
Posts: 40

Posted: Sat Jun 13, 2020 10:04 pm Post subject: Re: Surplus Wire

Unfortunately I won't be selling it.



I have harnesses for several things, so this will be at most two dozen circuits. Of which I can carry power and ground through one cable. So hey each one gets a wire for future use and a shield...

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BMC_Dave

Joined: 04 Jul 2018
Posts: 40

Posted: Wed Jun 17, 2020 1:12 pm Post subject: Re: Surplus Wire

The shield is sized for the combined current of the wires right? I'd like to use it for the other current conductor if I can.

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ceengland7(at)gmail.com
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Posted: Wed Jun 17, 2020 1:50 pm Post subject: Surplus Wire

On Wed, Jun 17, 2020 at 4:23 PM BMC_Dave <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)> wrote:



 	  Quote: 	
		  --> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com (bmcdave85(at)gmail.com)>

 

 The shield is sized for the combined current of the wires right? I'd like to use it for the other current conductor if I can.

 

 



	
*In general*, that's not a bet I'd make, because shields are, well, shields. You don't normally see them carrying serious current, in the sense of actual power (RF transmission lines obviously excepted).  Having said that, if we're still talking about 24 awg wire, it's extremely unlikely that the shield would be any smaller than that. If you're talking about using the shield for a single circuit's ground return, it sounds reasonable, but check for yourself by stripping a conductor, measuring approx. dia. with calipers, and then do the same with the shield 'drain' wire, assuming that it's a foil style shield. If it's braided copper strands, then the effective gauge might well be much larger than the combination of all 5 conductors combined. Just check it. Compute cross sectional area for a bare 24 awg wire, and do the same for the shield drain, using the basic pi * r^2 formula for the area of a circle.

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nuckolls.bob(at)aeroelect
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Posted: Wed Jun 17, 2020 4:07 pm Post subject: Surplus Wire

At 04:12 PM 6/17/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com>



 The shield is sized for the combined current of the wires right? I'd like to use it for the other current conductor if I can. 	


  NO . . . it's for conducting the products of electro-static

  coupling. Essentially zero current.  Run AMPs through

  a known length of shield, measure voltage drop through

  that segment. Compute the AWG equivalent from the

  resistance values in a wire table.



 

 

   Bob . . .

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BMC_Dave

Joined: 04 Jul 2018
Posts: 40

Posted: Wed Jun 17, 2020 6:55 pm Post subject: Re: Surplus Wire

Looking at the BMS13-48 spec the flat shield is tin coated copper, 0.0015" +-.0004 thk and 0.020" wide. I counted 16 strands in the braid I disassembled.



So 0.02"x.0011"x16 is 0.000352 sqin area, which is between 13-14ga (13.6, apparently). So that's what, 20ish Amps conservatively?



So the 5x 24ga conductors, slightly de-rated to 10A, seems the shield would be more than up to it.

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 18, 2020 6:40 am Post subject: Surplus Wire

At 09:55 PM 6/17/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "BMC_Dave" <bmcdave85(at)gmail.com>



 Looking at the BMS13-48 spec the flat shield is tin coated copper, 0.0015" +-.0004 thk and 0.020" wide. I counted 16 strands in the braid I disassembled.



 So 0.02"x.0011"x16 is 0.000352 sqin area, which is between 13-14ga (13.6, apparently). So that's what, 20ish Amps conservatively?



 So the 5x 24ga conductors, slightly de-rated to 10A, seems the shield would be more than up to it. 	


  Not sure about your numbers. 14AWG solid wire is .065" diam. 3.14 x (.065/2)^2 = 0.0033 sq"



  so I think your shield cross section compared to 14 AWG is off by a factor of 10?



  24AWG is .02" diameter for a cross section of 3.14 x (.02/2)^2 = 0.000314 sq" x 5 strands

  is a total of 0.00157 sq".  Working backwards I get a diameter of 0.0447 which is

  pretty close to 17AWG wire for equivalent resistance of the bundled strands.



  I get 0.00048 sq" total cross section for the shield which works back to a

  0.0247" diameter wire - just a tad smaller than 22AWG.



  Keep in mind also that when the shield is a power path for

  currents in central conductors, temperature rise is promoted

  by BOTH current pathways under a single jacket.



  I've used shields as return paths for countless, low

  power or signal pathways but I'd have to think long

  and carefully about pushing that combination of

  conductor/insulation to its thermal limits.



  What application are you considering where you find an

  advantage in using the shield for this wire as a power-path?



 

 

   Bob . . .

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BMC_Dave

Joined: 04 Jul 2018
Posts: 40

Posted: Thu Jun 18, 2020 7:03 am Post subject: Re: Surplus Wire

Yeah I got my zeros mixed up there. The shield is equivalent to a single 24ga wire, so that kills the idea. Thanks.

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