Originally Posted By: Brian A. Goodman
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The ground wire definitely should not be with the neutral on a subpanel. Subpanels really aren’t that complicated if you stick to looking for how it should be done, and just recognize that anything otherwise is wrong.
Here are the basics you're looking for:
There should be 4 wires instead of 3 (2 hots, 1 neutral, 1 ground). The usual rules apply regarding wire size vs. ratings / load / etc.
There should be 2 terminal bars (ground bars) instead of 1. One bar gets only
the neutrals (typically white) and is never
bonded. The other gets all of the equipment grounds (typically bare or green) and must
be bonded. The two bars cannot be connected to each other in any way, so if there is a factory installed jumper bar between them it must be removed for use as a subpanel.
If it's in the house that's about it, except for the usual panel inspecting details (branch wiring, etc.).
it's in a seperate building:
it must have its own grounding electrode (typically a ground rod, metal water pipe, rebar, etc.).
it does not require any of the above (4 wires, 2 bars, etc.) only
if there is no continuous conductive path between the buildings. In that case it can be wired just like a main panel. Watch out for metal fences, sidewalks with rebar, metal water pipes, telephone or TV cables, etc. When in doubt recommend the full-blown subpanel configuration, it's safer.
If I'm erring or leaving anything out, somebody speak up.
I'd strongly recommend the book I mentioned above to anyone in our business (Electrical Inspection of Existing Dwellings). It was written by the same guys who make Code Check. I like it because it's more conversational and comprehensible than a code book and written specifically from an inspection angle. Just bear in mind that it's not a code book if you need exact or obscure details on specific items.