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i'm replacing an old 220v receptacle in my shop with a new one that mates with a plug on a dust collector i just got. when i removed the existing receptacle it had two hot wires, a neutral, and no ground. when i went to add the new receptacle, i observed it takes two hot wires, a ground, and no neutral.

the wiring all goes through 1/2" metal conduit that connects directly to the sub panel. the sub panel is connected to a larger piece of conduit that runs through the ground to the main panel in the house.

none of the other outlets in the shop seem to be grounded.

what's a safe way to connect this new outlet that requires a ground?

e.g.

a) connect a bare copper wire to the outlet box, allowing the conduit to act as ground

b) connect the neutral wire to the receptacle's ground, since it eventually grounds at the main breaker

photo showing inside the sub panel, wires connecting this circuit identified by green circles:

photo of the new receptacle that i started installing before noticing it has a ground and no neutral:

2 Answers 2

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The metal conduit IS the ground

Welcome to EMT metal conduit. I have whole buildings of the stuff and not a green wire in them. I own 10 colors of THHN wire, none green.

Your receptacles pick up ground via hard-flush, metal-metal contact between junction box and receptacle yoke. This would not work if the receptacle was floating above the box metal on drywall ears, or if anything was painted or rusty, or if it had the cursed little paper squares on the mounting screws. But since you don't have those problems, your receptacle will auto-ground when you mount it.

It will fail ground test until you mount it.

b) connect the neutral wire to the receptacle's ground, since it eventually grounds at the main breaker

No, no, never! Location is everything. The fact that you have a neutral-ground equipotential bond in the main panel does not make all ground wires redundant.

In fact, if you cross neutral and ground, it isn't ground anymore. It's neutral. Notice all neutral wires are insulated? For reasons. Misusing neutral for ground can result in all your local grounds becoming energized when the reason happens.

Modern code even requires neutral and ground wires be separated for the run from the main panel to the subpanel, because subpanels used to bootleg ground off neutral.

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  • so hook up the two hot wires, attach nothing to the ground and i’m good to go? sounds great
    – schpet
    Commented May 12, 2022 at 23:13
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    Note: this subpanel does bootleg ground from neutral. You can see the white feed to the neutral bar, and the white jumper back to the conduit nut.
    – nobody
    Commented May 13, 2022 at 3:15
  • @nobody that was legal pre-2008. Hopefully OP will feel inspired and decide to pull a proper ground wire into that pipe. Psst: bare or insulated #8 copper, or insulated #6 aluminum. Commented May 13, 2022 at 3:37
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Can use the metal conduit as ground.

In the sub panel will need to remove the neutral to ground/conduit wire. Neutral cannot be bonded to ground in sub panels.

Metal under ground is not for life, it rusts/corrodes. Will probably need to add a ground rod connected to sub panel, so you know you have ground.

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