2 12/2 Romex Cable inside 3/4" outdoor metal conduit.


Old 09-19-20, 10:02 AM
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2 12/2 Romex Cable inside 3/4" outdoor metal conduit.

I bought my house and there is a shed in the back with electricity being run via a single 12/2 Romex Cable fed through a 3/4" metal conduit. The conduit is about 30 ft long, about 15 ft of which is buried underground. I trip the breaker often with power equipment and a vacuum running at the same time, so I want to run a second circuit. My plan was just to get a second 12/2 Romex Cable and feed it through the same 3/4" metal conduit to the breaker box. Depending how I feel at the time I'll either try adding the breaker myself or call an electrician to do that part. But I'd at least like to run the cable to save time and money. Is there any issue with running the second cable in the same conduit? Also is there some best practice for leaving the cable sitting in/near the breaker box until an electrician could connect/install a new breaker?
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Old 09-19-20, 10:19 AM
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Hi, Romex can not be run in conduit under ground, best bet is to pull out the old Romex and pull in individual THWN conductors, and I believe you are only allowed 1 circuit to a detached garage, go luck getting an electrician to connect up your work.
Old 09-19-20, 11:04 AM
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So what's a real solution then? Just run a long extension cord for the vacuum in the shed?
Old 09-19-20, 11:37 AM
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Is it really Romex? Romex® is a brand name. NM-C is the technical name. Are you sure that it isn't UF cable? Usually gray.

Easiest option may be to pull out the existing cable and replace with 4 individual wires. THHN/THWN 12 gauge red, black, white, and green. Then connect to double pole 20 amp breaker making it a MWBC. Need a double pole switch at shed as disconnect. This would essentially give you two 20 amp circuits to use in the shed.
Old 09-19-20, 11:49 AM
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While it does not meet code to run romex in conduit it is done pretty often by diy electricians. My last house had a little workshop about 40' away from the house and the power was run with 12/2 wg romex through 3/4" conduit just like yours. I meant to redo it but never got around to it. I never had a problem with it but the loads in my shop were minimal. Can you run another piece of romex through the same conduit? You can but then you'd out of compliance twice. The main problem is the romex insulation retains heat and it cannot escape out the conduit so 2 pieces of romex = 2 times the heat. If I were you I would consult an electrician to see what the cheapest and easiest way would be to do yours the RIGHT way.
Old 09-19-20, 01:36 PM
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Running two separate cables supplying power to an outbuilding is a NEC violation. Running NM-b in conduit is not a violation if above ground and inside a structure. NM-b (Romex) is not allowed outside or below ground either in or not in conduit because it is not rated for installation in wet areas. In wet areas there is a chance of cross shorting between conductors because of moisture. The best solution is to pull out the old cable and use it to pull in a new 12/3 UF-b cable and have a multiwire circuit giving you two 20A circuits. Now the question arises is the current conduit a complete conduit system and is it buried to the proper depth (18in.)? If it's a complete conduit system then you can pull 4 conductors of THHN/THWN as earlier mentioned.

Last edited by pattenp; 09-19-20 at 02:10 PM.
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