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I am installing 2 outlets in my basement. A buddy is an electrician and is going to come over next weekend and take care of the hookup and breakers inside the service panel. My job is to physically install the (dead) receptacles and conduit, and run the wire from the receptacles to the general area of the main service panel. But again I'm not doing any live wiring or breaker hookup. I'm just laying the ground work.

One receptacle will be a 20A, 120V branch circuit going to a 3-pronged duplex. The other receptacle is actually a NEMA 14-30 outlet running off a 30A and 240V circuit that will be protected by a 240V GFCI breaker. The former can be served (correct me if I'm wrong) by a 12-gauge wire, and the latter (the NEMA 240V) can be served by a 10-gauge wire.

Looking at the big box store websites, there are many different types of electrical wire. I believe I just need hot, ground and neutral wires bundled inside the same cable for both receptacles. So I believe I need "Romex" NM-B wire for both of these outlets, can someone please confirm or correct me here? Anything special for the 240V one because its GFCI?

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  • On the one hand you say you are in conduit. On the other had you talk about running wires "near the panel" - please clarify, since normally conduit would be run all the way to the panel - then wires are pulled into the conduit after it is completely assembled.
    – Ecnerwal
    Jan 8 at 15:23
  • I'm planning on: (1) installing PVC junction boxes on my concrete walls (tapcon screws), (2) running PVC conduit up the wall and securing it to the wall with tapcon screws + conduit hangers, (3) running wire from junction boxes, up the conduit, across my ceiling joists (using staples/fasteners) and ending it at my service panel. I'll leave enough room on both ends so that there is plenty of excess wire. Jan 8 at 17:24
  • So, you appear to be talking about cable, not wire, unless you will use a junction box at the top of the conduit to transition from cables across the ceiling to wires in conduit.
    – Ecnerwal
    Jan 8 at 17:29
  • Yes my question is: can I accomplish all my needs with Romex? Jan 8 at 17:35

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Per further comments, this answer does not actually apply, as the conduit is only serving as a sleeve. You are (per your statements in the question) in conduit so you do NOT want cable, at all.

You want THHN wires. If your conduit is solid metallic (EMT, typically) that is your ground, you don't need a ground wire. If it's not that, you'll need a 10Ga Green or Bare ground wire which can serve both circuits if they share the conduit. I'm assuming your conduit extends all the way to the panel - if that's not the case, please clarify.

You'll want 10Ga white (or gray) and (colors other than green, white or gray) and 12Ga white (or gray) and (a color other than green, white or gray)

For your own sanity, make the 12Ga hot color different from the 10Ga hot color(s). The 10Ga hots can be the same color as each other, as it does not matter "which is which." You could make all three the same as you can tell that one is 10Ga and one is 12Ga, but why do that when you have 8 or 9 different hot colors available? (That's without even getting into stripes.)

The 240V circuit needs two hots, one neutral, and a ground. The 120V circuit needs one hot, one neutral, and a ground. The ground can be shared, the neutral cannot.

The GFCI makes no difference to the wiring (or cable.)

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  • Thanksfor this answer. The purpose of the conduit in my mind is more aesthetic since these receptacles will be hanging halfway down my basement walls and I think PVC conduit both looks nice and also keeps people from touching the wires and fiddling with them. So I don't think Romex cabling would hurt even though its running inside conduit. I don't want to use metal conduit because I think it looks ugly. No conduit will only run up the wall and will end at the ceiling. From there I will keep the cabling suspended via staples/fasteners to ceiling joists. Jan 8 at 17:35
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    Then it's serving as a "protective sleeve" and the other answer applies. Hopefully you don't need both cables in one conduit (that would have to be very fat) - a single 10/3 and a single 12/2 are more easily managed in reasonable-sized conduit.
    – Ecnerwal
    Jan 8 at 17:41
  • Thanks again, so no there will be separate conduits. Can I just run 10Ga Romex through one conduit (going to the 240V NEMA 14-30 receptacle) an run 12Ga Romex through the other (going to the duplex)? Jan 8 at 18:02
  • With separate conduit (in "protective sleeve" mode per code language) stubs to separate outlet junction boxes, should not be a problem.
    – Ecnerwal
    Jan 8 at 19:05
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Random bit of pipe as a damage shield

TLDR: any pipe or bent metal will do, and conduit rules don't apply.

If you are just using a stick of conduit here and there as a damage shield for the area that is low on the wall, then any piece of metal will do - you don't need to use conduit or even think of it as conduit. (old gas pipe? 2x4 with a slot in it?) As long as the cable physically fits, that qualifies. You can come down to a junction box and use conduit fittings to get the (iron water pipe?) into the junction box. The top of the pipe doesn't need any fittings at all, but you must de-burr the pipe, which your wedge-shaped multi-tool is designed to do.

My go-to for that is a $1.00 "4x4" junction box with a 99 cent domed cover for 1 or 2 receptacles. You can bring in any threaded pipe by using 2 conduit nuts back to back. I enter that with EMT thin-wall metal um yeah, conduit with a coupler, because it's great protection and it's low profile. Also I have loads of it lying around lol. Since you're not using it as conduit per se, there are no conduit fill rules other than "don't damage the wire". 10/3 NM can be crammed into 1/2" trade size conduit if the 10/3 is round. If it's flat, you'll need at least 3/4".

Conduit as a full-and-proper wiring method

On the other hand, if you were running conduit as a wiring system...

Presuming that you are running the entire run in conduit, which is a great system...

Remember -- you MUST build the conduit EMPTY and then pull the wires into it after the conduit is completed. If that is making you nervous, then you might be planning the conduit incorrectly. Access points must remain accessible forever. Curves must be sweeps unless they are a "conduit body" or junction box with an access cover. Splices require larger junction boxes not conduit bodies.

Harper's rule: buy the wire LAST. It's best to wait until as late as possible to buy wires, so you benefit from more collected knowledge. I.E. build the conduit before you buy wire.

In fact, check with your buddy - who may have big spools of this wire far cheaper than the "short spool" or by-the-foot prices nearby, and in more colors.


With THHN wire, your ideal selection is:

  • two #10 black
  • one #10 white
  • one #10 green or bare
  • one #12 blue (can be red or black)
  • one #12 gray (can be white)

You only need one ground wire which both circuits can share.

On the 240V circuit, both "hot" wires should be the same color IMO. There is no useful use to using red & black here, because there's no value in distinguishing the phases. You are much better off using black-black, so if later you want a second 240V circuit in the pipe, you can use red-red.

The 20A circuit is also allowed to use #10 wire, but you really would need unique wire colors at that point, or a good method of wrapping with tape to identify conductors. (shrink tube being ideal). Tape and labels tend to fall off.

You are allowed to tape white wires in conduit - this does not change them from neutral to hot wires.

As things are, you can use black and white #12 and "get by on feel", but if you have gray and another color available, I'd say "use it".

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  • Thanks and +1 -- could I run 10Ga Romex for the 240V NEMA 14-30 receptacle, and 12Ga Romex for the 120V 3-pronged duplex? Jan 8 at 18:03
  • @hotmeatballsoup you can, but the conduit will have to be absolutely enormous 1-1/4" diameter stuff, because of conduit fill (Romex is not flat, and twists, and the pipe must be spacious enough to allow it to be pulled (past each other). You'll go broke buying pipe lol. See if your buddy can supply the wires - it's cheaper off a friend's large spool than buying small spools at retail or by-the-foot. Jan 8 at 18:08
  • I suppose I could Romex from the service panel to the spot where the cable enters the conduit and just use a cable ripper to expose the hot/neutral/ground from that point down to the junction box, right? Then I could use smaller-diameter conduit, right? Jan 8 at 18:36
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    No, you cannot do that. Read my cable answer. The cable jacket must be intact to at least 1/4" inside the junction box, at the other end of the conduit. But you are not trying to put both cables in the same conduit, so it's simpler. The way you stated it in you question has confused the issue by starting us from a point of "running wires in conduit" which is not really what you are doing.
    – Ecnerwal
    Jan 8 at 19:03
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    @hotmeatballsoup Sorry, I misunderstood what you were trying to do. Just as a damage shield for coming down the wall, any ole stick of pipe, bent metal etc. will do. For a class act, enter a junction box as if it were conduit. Jan 8 at 20:02
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If you are not, in fact, in conduit all the way, or the conduit is only serving as a short protective sleeve, you will want 12/2 NM-B and 10/3 NM-B cables for the 120V 20A and 240V 30A circuits, respectively. A cable is several wires inside an outer jacket.

12/2 has white, black, and bare ground in a cable jacket. 10/3 has white, black, red, and bare ground in a cable jacket. The grounding wire is "not counted in the name" of this type of cable.

The GFCI makes no difference to the cable. The 240V circuit needs two hots, neutral and ground, which is why it needs /3 cable, not /2 cable.

The jacket of the cable must be maintained intact at least 1/4" inside the box (which makes it miserable to get through conduit, or you need very large conduit to get it in comfortably.) The wires of the cable should extend 6" past the face of the box.

NM-B cable cannot be used in a wet location (you say this is inside the basement, so likely fine.) UF cable is needed if using cable in a wet location (all exterior conduits are defined as wet, but for an exterior conduit, which is NOT a "short protective sleeve" you would use THWN wire, and you'll find that virtually all THHN wire is also marked THWN or THWN-2.)

You should have a cable clamp on the entrance to the conduit to secure the cable. That will require having a fitting to connect the cable clamp to. Typically that would be a female threaded fitting to accept a male threaded cable clamp.

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