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# how many current carrying conducters

#1
06-20-12, 07:14 AM
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Join Date: Jun 2012
Posts: 2
how many current carrying conducters

How many #12 AWG current carrying conducters in 1/2 IN conduit if ambient temperature is more than 90F?

#2
06-20-12, 07:38 AM
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The amount of conductors allowed in a conduit is not affected by temperature. This is just based on conductor volume.

Derating the conductors based on temperature is a different story. The amapacities of conductors are based on 86 degrees F. For a 90 degree ambient you would need to derate to 0.91 or 0.94 depending on the temperature limit of the insulation or terminations.

#3
06-20-12, 07:55 AM
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Join Date: Jun 2012
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Max. #12 in 1/2 In conduit is 9 current carrying conductors
What I`m asking is after temperature derating how many #12 may I have in 1/2 In conduit..

#4
06-20-12, 08:13 AM
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You can still have 9...they just won't have as high a current capacity. At least that's the way I understand it.

Using the numbers already provided and assuming each conductor was rated for 20A, it would drop to 18.2 or 18.8 max.

#5
06-20-12, 09:51 AM
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The temperature is not the deciding factor. Conduit and box fill is based on the area of the conductors, not temperature or current carrying or not.

Also depending on the type of conduit and conductor insulation 9 may not be the correct number.

#6
06-20-12, 06:11 PM
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Location: Twin Cities, MN
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The max #12 THHN wires you can have in 1/2" EMT is 9.
The max you can have after derating for more than 3 current carrying conductors is 9.

Here is the math:
Ampacity of #12 THHN = 30 amps
derating factor for 9 wires = 70%
30 x .7 = 21 amps
Code240.4(D) 2008 says max amps for #12 = 20 amps

So bottom line is you can fill a 1/2" EMT pipe with 9 THHN wires, which is the max allowed for 1/2" EMT, and they can still carry the full 20 amps. Derating has no effect.

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