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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.

ziondreamt
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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.

JACK
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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.

Harper - Reinstate Monica
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