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Old 09-03-2008, 05:01 PM   #1
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


Hi all. Long time lurker, first time poster...

I'm in the middle of a major renovation on my 1864 house and I've gutted the entire upstairs including the rast's nest, cloth wiring.

I would like to create a new "core" in the attic where all the source lines running down into the new box are bundled in one PVC conduit and are distributed out to the outlets and lights from a centralized place. I've been reviewing the NEC and the fill factor charts but that mostly has to do with non-coated wiring and buried conduit.

I currently have BX wiring - are 9 wires too many to bundle together in a 1" PVC conduit that runs the length of the attic and is underneath about 3 inches of blown insulation?

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Old 09-03-2008, 06:53 PM   #2
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


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I currently have BX wiring - are 9 wires too many to bundle together in a 1" PVC conduit that runs the length of the attic and is underneath about 3 inches of blown insulation?


9 is fine, but if you have more than 9 current carrying conductors, derating becomes an issue.

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Old 09-03-2008, 08:03 PM   #3
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


Depending on the part of the country you are in... you may be required to derate for ambient increases in the attic, especially if conduit is ran under the insulation. For 9 current carriers as an example using 12 awg copper thhn in conduit is 21 AMPS. If I have a temperature of 105F according to locality for indoor attic ambient (summer). I have to derate the 21 amps another .82 to 17 amps requiring either a downsizing of the ocpd (circuit breaker which would be normally 20 amps))or upsizing the wiring to 10 awg. In reality you probably will have a mix of wiring sizes and they will be derated accordingly if needed.
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Old 09-04-2008, 10:22 AM   #4
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


I think he means 9 cables, not 9 wires?
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Old 09-04-2008, 11:07 AM   #5
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


Yeah that's possible but if so he can't do what he asks. You cannot run cables in that manner. His closest option if that is the case would fall under NEC 312.5(C) exception a-g.
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Old 09-04-2008, 09:37 PM   #6
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


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I think he means 9 cables, not 9 wires?

I was under the assumption that he he redoing what was existing. But I could be wrong.
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Old 09-04-2008, 10:08 PM   #7
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Creating a "core" electrical distribution source with PVC conduit - fill factor?


I wonder if you can get 9 cables in 1" pvc...... Or maybe I should say how far you can get them into the conduit....before.....

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