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I need to wire up a NEMA 6-20R and have both 12/2 and 12/3 cable available to me. Most diagrams I’ve seen show the hot’s to the horizontal spades (X and Y) and the bare ground to the Ground lug on the outlet.

I’ve also seen a 12/3 diagram that shows the two hot’s to the X/Y spades and the white/neutral wire bonded to the ground wire before connecting to the Ground lug on the outlet.

In either case, given I’m using metal 1-gang adjust-a-boxes, I’m assuming I’ll run the feed line ground to the box first, then to the outlet, with/without the neutral wire, depending on how you suggest. Can anyone please confirm my plan and advise on your preference for 12/2 or 12/3? Thank you in advance!

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NEMA 6-20 does not use neutral at all.

You're welcome to use 12/3 cable, but you'll be capping off the neutral and leaving it in the back of the box. That can be useful if you ever convert it to other uses, such as a Multi-Wire Branch Circuit (MWBC) supporting both 120V and 240V loads. Yeah, you can do that.

White or gray = neutral. Green or yellow/green = ground. Others = hot.

If you use 12/2 you must mark the white wire a hot color with tape, paint or shrink tube. The ideal aesthetic choice is red. Are you caught up now? :)

There are several ways the receptacle can pick up ground off the metal box - a hard flush clean metal-on-metal contact with the box will suffice, or an outlet labeled "Self-Grounding" will pick it up off the mounting screws. The telescoping box may affect this; read instructions. Or you can add a ground jumper to a proper ground terminal on the steel box.

The two hot terminals on breaker and receptacle go to black and "red" wires. Easy as that.

Remember if you are in NEC 2020, and if your state hasn't deleted this requirement, you need GFCI protection at the receptacle if it is in a garage or basement, outdoors, anywhere near a sink, or several other places. The only way to protect a NEMA 6-20 receptacle is use a GFCI breaker. In that case the GFCI's curly pigtail neutral must be wired to the neutral bar in the panel, but the neutral terminal on the GFCI is ignored.

I’ve also seen a 12/3 diagram that shows the two hot’s to the X/Y spades and the white/neutral wire bonded to the ground wire before connecting to the Ground lug on the outlet.

No, that's wrong. I could see possibly grounding the neutral on the supply end (heck, most panels the neutral bar and ground bar are the same bar)... but on the outlet end it MUST be capped off. Don't leave it bare; neutrals are sometimes hot, hence the insulation.

Grounds are green, yellow-green or bare. Nothing else is ever, ever, ever grounded, except for the Neutral-Ground Equipotential Bond in the main panel. (which sometimes takes the form of the whole neutral bar).

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  • 240 only needs two hots and a ground. But you need 120, which requires a neutral, +1.
    – Mazura
    Commented Nov 12, 2022 at 2:28
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    @Harper - your comments are always EXACTLY what I need. I used 12/2 and taped white to red. I’ll tape white to red in the receptacle boxes and use black and red wire for the pig-tails too. Type CH 2-pole GFCI breakers were $200 each - I wasn’t ready for that. Too bad there isn’t a GFCI in NEMA 6-20 :-(
    – riffin-rich
    Commented Nov 12, 2022 at 13:49
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Do NOT wire up neutral and ground together. That is a waste of a wire and adds to the perpetual confusion over neutral vs. ground.

For a 6-20, 12/2 is all you need. It is not unusual to use /3 cable for certain appliances or receptacles just in case you need neutral later. That is certainly the case for things like ovens and cooktops - many require neutral for lights/controls but many do not. However, it is less common to find much use for a 120V/240V combination at 20A (NEMA 14-20) than at 30A (NEMA 14-30 - common for clothes dryers) or NEMA 14-50 (RV power).

A lot depends on usage. Based on a comment, this is for a woodworking shop with lots of 240V tools. A shop like that will almost certainly also need 120V receptacles for smaller tools and other devices. Which leaves two possibilities:

  • Separate 240V and 120V circuits

Use 12/2 for 120V receptacles (hot/neutral). Use 12/2 for 240V receptacles (hot/hot). No 12/3 needed anywhere.

  • Multi-Wire Branch Circuits (MWBC)

These use 12/3 for hot/hot/neutral and let you connect any combination of:

  • 120V 5-15 and 5-20
  • 240V 6-15 and 6-20
  • 120V/240V 14-15 and 14-20

But the last one - a hot/hot/neutral 120V/240V combination receptacle is relatively unusual. 14-30 is quite common (clothes dryers) and 14-50 (RV hookups).

Using an MWBC to get 2 x 120V connections with 12/3 instead of 2 x 12/2 used to be quite common. But your use case would be to share it with 240V receptacles. Since you will have multiple 240V receptacles on each circuit, throwing 120V receptacles on the same circuit is an extra bonus.

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  • it’s actually the first in a string of three 240v outlets for woodworking machines. There will be a second string of three 240v outlets as well. Basement workshop.
    – riffin-rich
    Commented Nov 11, 2022 at 2:38
  • Aha! That is useful information. And all 15A or 20A receptacles? Will you also have 120V receptacles?
    – manassehkatz-Moving 2 Codidact
    Commented Nov 11, 2022 at 2:45
  • So on 12/2 MWBC, Black to X, Red to Y, and Ground … no neutral? To answer more specifically, it’s actually the first in a string of three 240v outlets for woodworking machines. There will be a second string of three 240v outlets as well. Application is a home wood-shop. Think two strings, 1 and 2, outlets are separated by 8’. 1A——8’——2A——8’——1B——8’——2B——8’——1C——8’——2C. I will only pull power from two adjacent outlets at the same time. 1A is Table Saw. 2A is Dust Collector. Then I might use 2A and 1B (Dust Collector and Band Saw). This way I’m always pulling power from two different breakers.
    – riffin-rich
    Commented Nov 11, 2022 at 2:50
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    If it is only 240V and 12/2 it isn't an MWBC, it is simply a 240V circuit. No neutral, black to one hot, white (should be marked with black or red tape) to the other hot, ground as described (to metal box, etc.) and no neutral.
    – manassehkatz-Moving 2 Codidact
    Commented Nov 11, 2022 at 2:56
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    At higher sizes (e.g., 10 AWG for 30A) it is a little different. But at 12 AWG/20A, almost everything is either 120V or 240V, not a combination. With your setup, someone could always switch it all to 120V circuits (moving white to neutral and using single breakers instead of double breakers) and with multiple circuits already in place they really won't need MWBC even if they (for example) hook up lots of 120V computers, etc. So 12/2 is good here. Just mark the whites with colored tape (not green!) to match the "white is hot" configuration.
    – manassehkatz-Moving 2 Codidact
    Commented Nov 11, 2022 at 3:08

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