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I am removing two 15 amp breakers at the top left of my 40 space electric panel to be replaced with a 2 pole 30 amp breaker for backup generator. Can I just run two THHN #14 wires through a flexible conduit from an adjacent sub-feed panel and use common ground and neutral on first 40 space panel?

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    – isherwood
    Sep 29 '20 at 20:00
  • I don't know the code references applicable but I'm certain you cannot do any of 1) use your load center as a junction box for a circuit being fed from a neighboring subpanel; 2) terminate a circuit's hot in one panel and its neutral and ground in a different panel. A lot of the rules are made for the next guy, so your electrical installation isn't a mess that's impossible to understand without de-energizing and tracing things out. It's not that what you want to do is unsafe immediately; but it might become unsafe when later re-configured by somebody who didn't know what you did. Sep 29 '20 at 20:59
  • @JeffWheeler -- 1) is OK provided you don't overstuff the loadcenter cabinet, which is actually quite a feat to pull off from what I've read, however, 2) indeed doesn't work so well Sep 29 '20 at 23:42
  • Are you trying to pull these #14 THHNs through the same conduit as the feeder wires to that adjacent panel, or a different conduit? The distinction actually might just matter here.... Sep 30 '20 at 1:17
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Ground yes. Neutral no.

You can do that with safety ground.

You cannot do that with neutral. Neutral needs to come over to the new panel that the hots are served out of.

This is easier to justify when using a type of metal conduit which itself is a valid grounding path, which is typically NOT the flexible kinds. EMT is a little more work but takes care of the grounds for you.

There are also good reasons to try to keep inter-panel conduits shorter than 24". Otherwise you are only allowed 4 circuits in them and must significantly derate the large feeder if there are other circuits in the pipe.

There is nothing wrong with using a service panel as a junction box to hold the wire-nuts that extend the circuit. Note this is a NEC interpretation, that may not work in Canada.

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  • If flexibility is not required flexible metal conduit is allowed as the grounding path NEC 348.60 the size is limited but using FMC as a ground path is legal. Since your wires are14 gauge they would be protected at 15 amps so FMC up to 1-1/4” 250.118.5 would be a code compliant grounding path. I do agree the neutral has to be from the same panel.
    – Ed Beal
    Sep 30 '20 at 13:44

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