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I am going to be installing three panels next to each other. Two of them will by side-by-side, and a third one will be vertically above the one on the left. (To clarify, it will be a load center on the right, an AC disconnect on the left, and a meter socket above the disconnect). This will be outside my house. I have confused myself looking at the different ways I can connect these panels together.

For the two horizontal panels, I seem to have these options:

  • A rigid nipple and two locknuts. Doesn't seem to be watertight since there's nothing pressing against the panel on the outside to form a seal.
  • A close rigid nipple and two watertight conduit hubs.
  • A rigid coupling and two chase nipples on the inside. Seems to be a nice watertight option, but unclear if the chase nipples have the "teeth" that bite into the panels to form the ground connection.
  • Two PVC male adapters, a short PVC conduit section, locknuts and bushing. Will probably require a ground wire to be run to keep the ground connection.
  • Rigid Offset nipple with locknuts and bushings. These seem to have a flange that presses against the panels on the outside.

As for the two vertical panels, I have a threaded hub on top of the disconnect. I was going to use a rigid nipple between the two, but it seems the same problem as above -- the nipple doesn't have anything to press against the bottom of the meter base on the outside to form a watertight seal. Is the right thing to use here a rigid nipple and then a water-tight conduit hub into the meter base?

A similar question -- for the side-by-side case, what's the normal way to make this connection when indoors? I have previously used a conduit between both panels and just a locknut on the inside of either panel. The tightness of the locknuts on either side press the nuts against the inside of both panels. Is that a code violation or is it OK?

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    Sorry, I'm a little confused, so answering as a comment, NEC 312.2 says "...entering above the level of uninsulated live parts shall use fittings listed for wet location." If you will notice construction of outdoor panels like homedepot.com/p/… often have factory co-centric penetrations on the lower side of 3R cabinet that provide no attempt to provide a water-tight seal, but the top has factory hub provisions. Where watertight penetrations otherwise needed search for myers hub. – NoSparksPlease Jul 26 '20 at 15:01
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Exterior panels are not normally hermetically sealed, and other than a top entry, no major attempt to seal them is required.

For the meter bottom entry, two locknuts (one inside the panel, one outside the panel) should be sufficient. You actually don't want the bottom of the box to be watertight - any water that gets in or condenses should be able to drain out, though in most boxes it can do that via the open side with the cover anyway.

Same for your question about side to side panels indoors - you don't just leave the conduit floating between locknuts in different panels - or you use one of the cast nipples (with no offset) or offsets that do have a shoulder for the locknut to press against. I would probably use the cast option (offset or not) for the exterior case, but I would not kid myself that it was waterproof, or that it needed to be, but it would keep the size of any water entry from rain hitting it and running sideways down to a minimum.

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    Yeah, normally with plain nipples, you'd use two locknuts on each box, with the outside locknut providing that "shoulder" for the inside locknut to work against – ThreePhaseEel Jul 26 '20 at 14:54
  • If i don't need to use anything special, when is the right time to use one of those watertight hubs? For example: this one – atanamir Jul 26 '20 at 17:38
  • @atanamir that's a great question. Please feel free to ask it, but not down here in the comments. – FreeMan Jul 26 '20 at 19:40
  • @atanamir read the first sentence of this answer... – Ecnerwal Jul 27 '20 at 0:43

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