Basic conduit fill code questions

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Old 04-26-11, 03:30 PM
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Basic conduit fill code questions

I’m running two new circuits, 12g romex cables, in parallel; however I need to run them through EMT conduit for protection while exposed inside a closet. Is it code to put two romex cables inside the same EMT pipe? (romex jacket included as I already have the required cable) Is it really necessary to buy THHN conductors and have two transition points (romex to THHN back to romex)?

What size pipe is required (regardless if one EMT conduit is needed or two)?

I was going to start and terminate the EMT conduit(s) with metal 1900 boxes…in which I would connect the grounds from BOTH 12g cables…it is code to safety ground a metal 1900 box from two different circuits?
 
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Old 04-26-11, 03:35 PM
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You cannot run two cables together for protection in a single conduit (unless the conduit is less than 24" long), but you could do one cable each in two 1/2" conduits. Use drive-on or screw-on bushings to protect the cable from getting cut on the sharp end of the conduits.

Not only can you connect the grounds, but you must connect the grounds of all circuits which share a box.
 
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Old 04-26-11, 03:51 PM
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Originally Posted by ibpooks View Post
You cannot run two cables together for protection in a single conduit (unless the conduit is less than 24" long), but you could do one cable each in two 1/2" conduits. Use drive-on or screw-on bushings to protect the cable from getting cut on the sharp end of the conduits.

Not only can you connect the grounds, but you must connect the grounds of all circuits which share a box.
So, in theory, it's code compliant if stray (safety ground) current from circuit #1, travels down the safety ground wire of circuit #2 (accomplished by attaching grounds to the same metal box)?

So, it would be acceptable to run one 3/4" EMT conduit so long as I convert the romex cable to THHN conductors inside the conduit? If so, is there any particular THHN conductor type I am looking for?
 
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Old 04-26-11, 03:58 PM
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Originally Posted by k19_1234 View Post
So, in theory, it's code compliant if stray (safety ground) current from circuit #1, travels down the safety ground wire of circuit #2 (accomplished by attaching grounds to the same metal box)?
Equipment grounds should only ever have current briefly during a fault situation, not during normal operation.

So, it would be acceptable to run one 3/4" EMT conduit so long as I convert the romex cable to THHN conductors inside the conduit? If so, is there any particular THHN conductor type I am looking for?
If you convert to THHN you can use a single 1/2" conduit. The issue is the thickness of the romex cable jacket and packing. Individual THHN conductors are substantially thinner so more can fit into a smaller pipe. Just plain ol' THHN in black, white and green/bare; you can use stranded or solid core at your choice.
 
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Old 04-26-11, 04:07 PM
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Originally Posted by ibpooks View Post
If you convert to THHN you can use a single 1/2" conduit. The issue is the thickness of the romex cable jacket and packing. Individual THHN conductors are substantially thinner so more can fit into a smaller pipe. Just plain ol' THHN in black, white and green/bare; you can use stranded or solid core at your choice.
But is there a particular rating that needs to be shown on the THHN wire? What's the difference from using wire stripped out of a romex cable?

I assume the wire colors need to remain in place? Black to black, white to white?
 
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Old 04-26-11, 05:04 PM
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What's the difference from using wire stripped out of a romex cable
The wires in NMb are unmarked and not approved for use ouside the sheath.

Have you considered building a wire chase instead? A 1X4 or 1X6 with edges beveveled at 45° and fastened in the corner floor to ceiling will do it. Easy to do you just need to trim back the base and shoe to accommodate it. Paint it and it will blend in and look even better than conduit. That way you can use the NMb you have. Just secure it before it enters the chase and fill the holes with fire-stop caulk.
 
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Old 04-26-11, 05:40 PM
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Originally Posted by k19_1234 View Post
But is there a particular rating that needs to be shown on the THHN wire?
THHN is the rating that would be printed on the wire, usually with several other ratings too. The T is for thermoset PVC insulation, the HH indicates a 90C temp rating, and the N indicates an outer layer of nylon insulation. Most of the time there will also be a W indicating use in wet locations.

What's the difference from using wire stripped out of a romex cable?
Conductors in romex might be the same as THHN if the mfr made it that way, but they are technically unrated without the overall cable sheath.

I assume the wire colors need to remain in place? Black to black, white to white?
Correct.
 
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