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WoodworkerDave 09-16-2008 11:57 AM

Feed to sub-panel questions ?
I'm planning on installing a sub-panel in my basement workshop to add 120 and 240 volt circuits in the shop. The sub-panel will be situated within 3 feet of the existing panelboard, but on an adjacent wall. I will feed the sub-panel through a 60 amp 2-pole breaker and use 6/3 plus ground NM cable run up, then over through a few ceiling joists, then down to the sub-panel (about a 12 foot run max).

My questions below concern the feed between the main and sub panels:

1. What diameter EMT conduit or FMC do you estimate I'll need to protect the 6/3 plus ground NM cable on the short run along the concrete basement wall from the joists to the panel? Any preference as to EMT vs. FMC?

2. Is plain NM 6/3 plus ground acceptable, or should I use NMC (if I can find it)? My basement is dry.

3. As an alternative, I was considering running 4 gauge THHN/THHW wire within FMC (3 wires plus ground) for the run, pending cost differences. This would allow me to go with a larger 80 amp feeding breaker. Does this sound acceptable? What gauge ground wire would I need?

Thanks for you help.


chris75 09-16-2008 06:25 PM

I wouldn't install anything to protect the NM. but thats just me... check this out...

micromind 09-16-2008 09:25 PM

The breaker size feeding the sub-panel depends on what you're powering.

In a woodworking shop, usually only one tool is running at any given time, except for a dust system. A 60 amp breaker will reliably start a 5HP motor, while a 1HP dust collector is running, but not much more, assuming both are 240 volt.

Unless it's in an area where it might get clobbered, I wouldn't bother to protect the NM feeder. If it does get smashed, the 60 amp breaker will trip.

If possible, I'd put the lights on a separate circuit fed from the main panel. That way if the feeder to the sub trips, you won't be in the dark.


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