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I am hiring an electrician to do the work so my question is more for my education and helping me ask the proper questions to the perspective contractors.

Purchased a condo recently and want to put in some recessed lights. The condo has a subpanel in the laundry room with the main service panel in a common area on the main floor. All the current wiring is run in metal conduit, I presume that it's THHN wiring. The subpanel has a neutral bar that's not bonded to the panel. The panel is grounded via a grounding wire that I would presume runs to the main service panel. There is no ground bus within the service panel.

So, my question. For the new recessed lights (6" LEDs), can one run nonmetallic sheathed cable (NM cable) not in conduit? Or must this be THHN in conduit. If one runs NM cable (again, not in conduit) would you install a ground bar in the sub panel to bond the romNM cable ground to it, or can the NM cable ground be bonded to the metal electrical gang box (ground clip?) that the switch will be in? In this case the switch for the new lights could go into an existing metal gang box (where there is currently a switch for a ceiling fan). This box has metal conduit back to the sub panel. So from the panel, NM cable to the existing switch box, from there NM cable to the recessed lights. I am wondering if this is possible, would one / should one install a ground bus in the panel or bond ground to the existing switch box.

I hope this makes sense and I just didn't completely confuse everyone.

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You have to bond the grounding conductor in the sub panel (where the circuit originates), you cannot bond it in a switch box (where the circuit terminates). You bond the grounding conductor in the sub panel, the switch box is then bonded using the grounding conductor, not the other way around. –  Tester101 Oct 13 '13 at 12:50
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Even when properly grounded at the panel, you cannot use the grounding means of one circuit as the grounding means for a new circuit, regardless if via conduit or wire. Also ensure your local jurisdiction allows romex for your situation. –  bcworkz Oct 13 '13 at 21:55
    
This is a pretty detailed code question. I'm new to this stackexchange but it seems solidly outside the format and very specific to code jurisdiction. –  Keith Hoffman Mar 5 at 6:34
    
@KeithHoffman I disagree. This question deals with how grounding and bonding work, not with the codes that govern the process in a specific area. –  Tester101 Mar 5 at 11:20
    
" For the new recessed lights (6" LEDs), can one run nonmetallic sheathed cable (NM cable) not in conduit? Or must this be THHN in conduit. " That's absolutely a code question with significant variation in jurisdictions. –  Keith Hoffman Mar 12 at 3:24
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I will do my best here. I take it the reason you are asking about using NM wire is to save money? Purchasing NM is much cheaper. You can still run NM inside the conduct if there is room left. So if your conduit is 3/4 inch. you maybe able to pull 14/2 wire through with Lube.

Your subpanel would need a separate ground bus since the conduct is considered the (Ground) By installing a Ground bus and using the NM 14/2 or 12/2 you must connect the Neutral and Ground separate as for the panel is not bonded. I believe the term is floating ground and neutral. Your Subpanel is connected to your Building since it is not Bonded. The question i have is why is your panel has only 1 bus bar? There should be 2 one for the Neutral and the other for the Ground. Your subpanel should have 1 Aluminum service line that contains 2 hots leads and 1 neutral and 1 ground. The other question i have is the service line coming from the Main Panel inside metal conduct as well? The gang boxes are grounded by the Conduct, but I would recommend you put a Pig Tail in the box.

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