I finally did my 50 AMP 15-40 Nema wiring. Couple of questions on it.

  1. I don't have enough ground and neutral wire to reach the ground bar of the electric panel. Is it ok to join both neutral and ground together, just before the two wires enter the panel, and take one resulting wire to the panel's ground bar? If both can terminate separately on the ground of the electric panel, why is it even separated at first? I understand one is for fault prevention and one for return path, but ultimately they do connect to common ground bar at the electric panel.

  2. In my 15-50 power distribution gang box, there was an existing wire connected from ground pin to the metal body of the box. I also have the ground wire connected to the electric panel on the same pin. Is that fine or only the ground until electric panel is enough? or should I also separately connect the metal box to the ground surface.

  • 1
    Nema 15-40? Do you mean 14-50? NEMA 15 is 3Ø. Commented Dec 13, 2019 at 21:43
  • sorry, yes 14-50
    – marc Katz
    Commented Dec 14, 2019 at 4:14
  • You know that it's A-OK to pigtail extra length on wires in an electrical panel, right? Commented Dec 14, 2019 at 5:55

2 Answers 2

  1. No, you can't do that because a single fault would make it deadly. Consider what would happen if the combined neutral+ground wire came loose in your panel -- all the current that was trying to return via neutral wouldn't make it, and instead it'd be able to flow back along the ground wire, energizing the chassis of your appliance with 120V. On the other hand, if they're separate wires all the way to the panel, either one coming loose won't create a safety issue. What you can do instead is put a junction box next to your panel, as far as the current wires reach, then splice to a short length of new wire to get the needed reach.

  2. You shouldn't put two wires on the receptacle screw unless it's meant for that, and it's probably not. A better way of doing it is to pigtail the ground to the receptacle: wire nut the box ground, the receptacle ground, and the incoming ground wire from the panel together.

  • 1
    Agree with Nate, but will add that to my knowledge, pigtails are allowed inside electrical boxes, so if you have enough wire to bring into the box, you can pigtail them to the bus(es). The junction box solution works perfectly well too, but keep in mind it has to remain accessible, so it may be an eyesore if the space is finished.
    – clwhoops44
    Commented Dec 13, 2019 at 19:58
  • Thanks! What are the issues if I wire the metal box of the 15-40 directly to the ground (soil) and leave the ground coming from electric panel connected to ground pin? Logically, it should exhibit similar behavior to pigtailing, no?
    – marc Katz
    Commented Dec 13, 2019 at 20:47
  • Also, I like all responses on why connecting ground and neutral before the panel is a bad idea. May I ask somewhat related question? I have a 6 gauge ground, will it be an issue if I twist multiple smaller copper wire together, let us say #12 and tie to the #6 wire? or should I only go for another #6 copper wire to avoid issues?
    – marc Katz
    Commented Dec 13, 2019 at 20:53
  • @marcKatz, if you simply connected that metal box to soil (a ground rod) and nothing else, no, it wouldn't be equivalent. It's a common misconception that all electricity wants to return to ground; it actually wants to return to its source. For natural electricity, such as lightning and static electricity, that is indeed ground, but for the electricity coming from the power company, it wants to go back to the neutral terminal of the transformer up on the pole. In any case, you already have a perfectly good ground right there in the box, so why not use it?
    – Nate S.
    Commented Dec 13, 2019 at 20:54
  • @marcKatz, that's fine to mix ground wire sizes; they just need to have their minimum wire size all the way from what they're protecting back to the panel. So if you're thinking of joining #6 from the receptacle and #6 back to the panel with a #12 to ground the box, that's fine.
    – Nate S.
    Commented Dec 13, 2019 at 20:56

Coming up a little short

You can always splice wires, but only inside junction boxes.*

What I would do is put a large steel junction box located so you have ample wire length for your splice (given your short wires). That is to say, don't short-skunk it and leave yourself only 2" of wire inside the box; give yourself a full 9-12".

Then, since the junction box is quite close, connect it to the service panel with EMT, IMC or Rigid conduit. What does this do? That metal conduit is usable as the ground path. Which means you can simply terminate the ground wire right there in the junction box; no need to extend into the panel. Then, in that box, you splice to extend the neutral wire. The last segment through the metal conduit only has 3 wires in the pipe.

I actually do this intentionally, in almost all my circuits. The reason is, I acquired a factory building where breaker thieves had cut all the wires at the edge of the panels. So I simply installed a bunch of boxes <24" up the conduits and spliced there. The splices have given zero trouble. They also let me transition from legacy solid wire to stranded wire for easy working in the panel. So I'm a fan of the technique, and even use it in places I don't need to -- they're a great place to stick $16 GFCI receptacles or deadfronts instead of $40 GFCI breakers.

Busy grounds in boxes

Remember ground wires are almost free in conduit fill calcs; you count only the largest wire once.

First, if you have a metal junction box, and your receptacle also has a metal yoke, and the receptacle sits hard-flush onto the metal screw-mounts on the junction box -- no gap, rust or little paper squares in the way -- then the receptacle grounds through this hard yoke-box contact. So you don't need a recep-box jumper wire. That frees up the ground screw on the junction box for your supply cable.

Or, you can drill multiple #10-32 holes in the junction box and have multiple ground screws. Legit!

Or, if you're really vexed by the need to ground multiple wires to the box frame, you can pigtail.

If that's too much for you (e.g. you are using #6 wire), then here's a cheat -- shop for "accessory ground bars" for service panels. Some are only 3" long and will fit nicely inside a junction box. Attach them flush (drill and tap a couple #10-32 holes if needed to mount them; don't put screw holes in removable knockouts). Then attach to the lug holes on the bar. That will slickly deal with #6 wire and aluminum wire, since they are aluminum rated.

* Or conduit bodies so large that they have sufficient cubic inches to qualify under the junction-box rules; however this may foreclose adding any more circuits to the conduit.)

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