Counting Conductors in a Conduit

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Old 02-06-06, 11:14 AM
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Counting Conductors in a Conduit

When counting conductors in a conduit (or passing through a hole in a beam) do you include grounds or only the neutral and positives?

How do you count when you have different gauges - e.g 10 #14 and 3 #12?

Finally what is the typcial insualtion type on romex cable used in typcial indoor construction (number of conductors permitted varies based on insulation type).

Thanks,

David
 
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Old 02-06-06, 11:45 AM
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Originally Posted by Montanaro
When counting conductors in a conduit (or passing through a hole in a beam) do you include grounds or only the neutral and positives?
The term 'positive' has no meaning in AC power; there are hots, neutrals and grounds. It depends on what you are counting for: for derating you count current carrying conductors, hots and neutrals; for conduit fill you count all conductors.

How do you count when you have different gauges - e.g 10 #14 and 3 #12?
For derating, each current carrying conductors counts as one. For conduit fill, you figure the cross-sectional area of the conductor.

Finally what is the typcial insualtion type on romex cable used in typcial indoor construction (number of conductors permitted varies based on insulation type).
Typical NM-B cable is constructed from THHN conductors with a PVC outer jacket, but that is irrelevant because the conductors are not listed for use with the outer jacket removed. When calculating conduit fill for cable assemblies, you calculate cross-sectional area of the cable as if it was round at its widest point. This means that a typical NM-B cable must be figured as if it was a 5/8" round cable. Running cables inside conduit, other than for protection over short distance, is considered bad practice and poor workmanship.
 
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Old 02-06-06, 12:37 PM
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David you may find this article helpful........

http://www.selfhelpandmore.com/homew...fill/index.htm

I should add though that the number of wires of various sizes is only part of the equation. You must consider ampacity deration and ambient adjustments in order to determine if the wires ampacity after you put it into the conduit with other wires will allow it to carry the load it serves.

You need to understand deration and how it differs from conduit fill. Then consider the two together for your final answer.
 

Last edited by Roger; 02-06-06 at 01:01 PM.
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