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I'm trying to clean up a situation where there's originally rigid metal conduit and no ground wires from the panel. Someone has added flexible metal conduit at several junction boxes down line that includes a ground wire in them. I'd hate to just leave unconnected ground wires floating in each of these boxes and want to confirm that I can attach them to the metal j boxes without running a new wire all the way back to the main panel (assuming that the conduit is making a good ground).

I found this one question here that might include the answer but I'm not quite sure it's the same scenario. Apologies if that makes this a duplicate.

No Ground Wires - Can I connect a wire to the metal box for ground?

Edit: this is in Florida, US. Commercial building.

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    We do not do commercial, but ground wires should be connected to metal boxes. A simple test for good ground is to test with a meter and should get ~120v between hot and ground. Box, wire and/or conduit. No 120v and you should be thinking of running a new ground wire or seeing where the problem is.
    – crip659
    Commented May 2 at 20:48
  • For what it's worth it's essentially a residential garage being used as a shop, I don't know why I added that last bit to the post. The conduit ground is good, I'd just like to confirm I can attach those wires rather than leave them unconnected.
    – ziondreamt
    Commented May 2 at 21:09
  • Grounds must be attached/continuous. Either to the box and/or the receptacle, light, switch(if plastic boxes). You want the grounds to be continuous if a device(outlet/light) is removed.
    – crip659
    Commented May 2 at 21:44

2 Answers 2

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Not only can you, code requires it if the length of FMC is more than 6 feet. Those ground wires should be connected together and then connected to their junction boxes. you do not need to run a ground wire all the way to the panel. I've seen and corrected many cases where the installer assumed the FMC was an approved ground no matter what the length... not true.

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  • Perfect, thank you! And I'm glad to know about the FMC part, I actually thought it was functionally equivalent to RMC for grounding, fortunately I have accidentally used it the correct way so far.
    – ziondreamt
    Commented May 2 at 22:27
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    FMC = Flexible Metal Conduit; RMC = Rigid metal conduit
    – D Duck
    Commented May 3 at 7:58
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I'm trying to clean up a situation where there's originally rigid metal conduit and no ground wires from the panel.

Metal conduit 101: There's nothing wrong with that.

You're perfectly welcome to use EMT, IMC and RMC metal conduit as your grounding path. Flex conduit, not so much.

If for ANY reason you want or need to double your metal conduit with a ground wire (e.g. an EMT run over a garage door that you just know is gonna get beaned by a forklift one day), run it between the junction boxes on either end. If you want a ground wire in every single conduit, then ditto repeated.

Or if you're running metal conduit to a plastic thing that needs a ground wire (dirty look at most EV charging equipment), you can pick that up from the last box.

If you install a ground wire, you must follow ground wire rules. The ground wire must ground every "junction box" it passes through, meaning any box with a device or splice. It does not need to ground "conduit bodies" i.e. a box with no splices or devices.

All ground wires must go to the metal box FIRST (as a higher priority). Ground spurs to a mounted device are often unnecessary but you are never allowed to run a ground wire straight to a device bypassing the box. The entire ground network must remain intact even if the device is removed.

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  • Understood, thanks. I probably should have condensed my question to: "If a junction box is using RMC as the only ground, can I attach a ground wire to that junction box for use further down the circuit without running a wire back to the panel?" But I wasn't sure if that was legible.
    – ziondreamt
    Commented May 4 at 6:26
  • @ziondreamt that makes sense, and answer is yes. Commented May 6 at 17:50

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