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I'm looking for some direction here. I have a detached garage that already has power supplied to it, and the structure is divided into garage space and a woodworking shop by a partition wall. The garage space is all exposed joists, beams, and studs, but the shop area is all finished. The panel is in the garage on an unfinished wall. I want to run a 20A 230V circuit to the partition wall for a single 230 receptacle, and an electrician has told me there's enough spare amperage to run the circuit. I'd have a run of about 15' to the wall, and then over a few more feet to drop it down the wall (the top of the wall is also exposed in the garage side, but is finished with OSB).

I spent some time as an apprentice electrician about a decade ago, so I have the tools and confidence, a healthy respect for the lethality of electricity, can generally read and understand NEC code citations, and I'm an anal retentive perfectionist who doesn't want to get sued or have anyone get killed.

So these are my questions:

  1. Should I use THHN in PVC rather than NM cable? If THHN, could I make a run up the wall and across the joists into a junction box, and then run NM down the wall?

  2. What's considered "workmanlike" practice when running conduit up studs and across / parallel to joists?

  3. I'm planning to use 12 gauge conductors for a 20A circuit - I'm under the impression this is what's advised? A dust collector is the only thing that'll be running on this circuit.

  • Is there conduit or NB cable in the garage now? I'm a big fan of conduit, either all the way or just way will work. 12 AWG is required for a 20Amp breaker... What's the load on the dust collector? – JACK Oct 19 at 16:21
  • Hello, and welcome to Home Improvement. We'll need some more info to help you, and you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Oct 19 at 16:24
  • @JACK There is indeed NM cable all over that space right now, pretty poorly installed, by a former owner I imagine. The DC is a Jet DC1200, and the plate says 15A @ 230V - I assumed that was a max draw and not an average. – swingsoneto Oct 20 at 17:14
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I would not hesitate to run EMT conduit the whole way, and for a very good reason: Alterability given that the wood shop is a finished space.

You're in a wood shop. You have things arranged the way you'd like now, but you may decide later you'd like to rearrange, or add something else. Add a circuit? Pop the covers off, pull 2 wires, punch em down, badabing.

And I like EMT conduit because over on the unfinished side, it provides physical protection without question. Sched 40 PVC is limited in its ability to provide physical protection.

Also, if you're drilling holes through joists to accommodate the wire or conduit, EMT lets you get the most through the smallest hole - up to 4 circuits in a 1/2" EMT pipe. With wood shop tools that even allows a couple of 30A/#10 tools.

I think 12 AWG is a good idea. I own 11 colors of stranded 12 AWG (just found blue-red at the Habitat for Humanity store) and none of 14 AWG. I need the colors for circuit disambiguation, much much much more than I need to save small coin on my few circuits that can be 15A.

There is one circumstance where you can put #14 on a 20A breaker (or #12 on a 30A) - but this is not a case of undersizing wire (you'd never do that). For certain motors, you are allowed to use the correct and proper size of wire for the motor, then up the breaker to avoid startup trips. To qualify for this, certain motor calculations are required.

  • And we all know what you use your yellow 12 AWG for. – JACK Oct 19 at 17:27
  • @JACK i swear, I should just unwind the whole roll, fold it at the halfway point and spool it back on so it comes of in 2 :) ... No seriously I do occasionally use it for switched-hot for the brown/white pair... – Harper Oct 19 at 17:43
  • @Harper I'll do some EMT shopping. So this brings me to one of my main curiosities about this space: there's a garage door that opens almost flush to the joists I'll be running conduit along and across. What's "code" when running conduit? Drilling through joists, or clamped to the tops (since I can't put them underneath)? What about a run parallel to a joist? – swingsoneto Oct 20 at 17:24
  • Also, is it acceptable to make the junction box on the top of the wall and run NM down the wall to the receptacle? I've wondered about mice gnawing on exposed NM - I know I've got a few of them running around in the ceiling of the finished side. I haven't seen any signs of chewing, but I suppose it could happen. Is there anything someone knowledgeable would do in that instance to protect a short run of NM? – swingsoneto Oct 20 at 17:31
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Personally, for interior work I prefer EMT - it's cheaper, it serves as a grounding path if you like (you can run a grounding wire, but you don't have to if the conduit is continuous and properly assembled), and it's unlikely to rust away inside (out in the weather I prefer PVC.)

EMT needs to be supported within 2 feet of boxes/terminations and at least every 10 feet. I.e. screw a clamp to the framing that often, or more often (remember, code is a minimum requirement.)

1/2" EMT will have plenty of room. As would 1/2" PVC if you go that route.

  • The "I don't wanna bend conduit" middle way would be 12/2 MC (or MC-light. Or AC but that's gonna take a real electrical supply.) No alterability as you get with conduit, but it's not wimpy like NM cable. – Ecnerwal Oct 20 at 14:59

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