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How should NM-B wire (romex) be run from an exterior panel to comply with California Electric Code 2019 (based on NEC 2017)?

Here are two ideas:

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Option 1: run THWN through an LB into an 8x8 box in the crawlspace, where the THWN is spliced (wirenuts) to NM-B romex. This avoids running the NM-B in exterior conduit, which is not allowed as it a 'wet location'

Option 2: run THWN through a nipple directly out the back of the panel box, into an 8x8 box in the crawlspace with same splicing to NM-B as Option 1.

Questions:

  1. Do both of these comply with California Electric Code 2019 (based on NEC 2017)?
  2. For Option 2, what fitting would be used between the nipple and the back of the panel to prevent water ingress? (see orange mark for location). Would that require extra siding to be removed to accommodate the fitting to allow the panel to sit flush?
  3. Is there a code compliant 'Option 2b' where no splicing is needed, and the the NM-B runs directly into the subpanel?
  4. Any better ideas?

I'm assuming I don't need to derate the ampacity of the THWN in either case, as the distance from panel to the box is <24", so no derating is required.

I'm curious - if the nipple/conduit in these designs is considered a 'wet location', then why is the 8x8 box not? Is it because any water in the conduit is assumed to drain out the bottom of the box without mixing with the wires? Just curious.

tom
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1 Answers1

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Both of these options are fine. The concept of a few feet of NM-B ran through a nipple and/or LB into exterior pipe due to the fact it is a WET location is nit-picking. IMO. If you run into a building inspector that calls you on 12 inches of Romex in a exterior conduit, your concern should not be THAT issue. Your concern should be dealing with a prick like this inspector.

If it were me, I would drop a pipe down to an LB, nipple from the LB into the crawl space leaving an inch or two of nipple sticking into the crawl space, then spin a pipe bushing onto the end of the nipple. Get my non metallic cable to that nipple with 8 feet of an extra length to extend into the LB and up into the panel. THEN, just strip the sheathing from the Romex and fish the conductors up into the panel. Silicone where the nipple penetrates your wall.

I have installed hundreds, maybe over one thousand service upgrades in my 36 years as an electrician and this is a minor hair splitting issue. My advice to you, don't get nervous about small details like these. Electrical theory and practice will present REAL issues that require REAL consideration regarding code and safety. THIS issue is not one of those issues.

David Brown
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