[RE-wrenches] Parallel Wire combining

Jarmo.Venalainen at schneider-electric.com Jarmo.Venalainen at schneider-electric.com
Tue Dec 2 16:26:06 PST 2014


Hi:

Look at it this way,

The three conductors in parallel can handle more current because they have 
more surface area with which to dissipate heat.  Or to put it another way, 
the heat from the middle of the thick 975 kCM cant get out and so the wire 
stays hotter.

See picture,



JARMO
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From:
Larry <larry at starlightsolar.com>
To:
RE-wrenches <re-wrenches at lists.re-wrenches.org>, 
Date:
12/02/2014 03:30 PM
Subject:
Re: [RE-wrenches] Parallel Wire combining
Sent by:
"RE-wrenches" <re-wrenches-bounces at lists.re-wrenches.org>



Hey boB,

This is the reference table I was using. They show 325 AWG and 325kCM 
refer to the same diameter cable but I should have used kcm for clarity. 

If all insulation/temp rating is the same we are back to my original 
question. Anyone else able to explain this? To be safe I am leaning toward 
using the combined CM number to size for current rather than 3 times the 
ampacity as that just makes no sense to me. 


On 12/2/14 3:54 PM, boB at midnitesolar.com wrote:

The "area" of the conductor will be 3 times and you would think that the 
NEC Ampacity would also be 3 times
that of one conductor.   But one LARGE conductor with the same area might 
not be as high as you think
because of insulation.  I would think that ampacity of 3 cables in 
parallel would be 3 times.  But probably
not when you take a single cable of the 3X area out of the NEC table.  (I 
haven't looked at this to verify)

Also,  Larry,  325 AWG 750 AWG (gauge) wire is a bit too small for this, 
don't you think ?

I know...  You mean circular mils...
boB



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