Wiring up exterior load center

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Xandrew245x

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I am upgrading my main panel, it is currently located outside, I replaced the meter can and installed a GE exterior load center.

I've wired up a panel before, but never dealt with an exterior panel. I can't seem to find much information on how to bring the NM cable from inside into the panel.

Most obvious choice would be conduit to a J-box, but from my understanding, if the conduit is longer than 24" then you would have to derate the wires, which would make that option completely not possible.

To do this I would come out the side of my panel, and would have to use a 6"-8" piece of conduit that is slightly bent into a LB through the wall. It would then go into the back of a J-box in my crawlspace. This run would be really close to being 24" long, and may even be longer than 24".

Another option I've seen is a nipple ran out the back of the panel into the interior wall, the NM cable is ran through the nipple into the panel. I know this is a code violation though since code states NM must be secured at the panel.

Thoughts?
 

wwhitney

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Option 1, the 24" length limit applies between enclosures, so you could have 24" from panel to LB, and then 24" from LB to junction box. The pipe segments under 24" wouldn't trigger derating, but you'd still be limited as far as conduit fill (but 60% instead of 40%, if I recall). And the NM cable would need to be secured to the junction box, which would most easily be done with multiple entries and clamps, each clamp being limited to the number of cables it is listed for.

Plus each circuit is supposed to be spliced in the junction box to THWN or one of the other options, as the innards of NM cable are not labeled and hence not an allowable wiring method in conduit by themselves. And the box needs to be sized accordingly. The EGCs can all be combined, though, with a single EGC sized to match the largest EGC in the cables involved, run from the panel to say a terminal bar mounted inside the junction box.

Option 2, the issue of securing the NM is the principal obstacle. You would need multiple NM clamps, so that each clamp only contains a number of cables up to its listing, so you'd need multiple nipples. The clamp could be installed reversed, with the clamp mechanism inside the panel, screwed through the panel into say a PVC female adapter, a short stub of PVC conduit, and then a PVC male adapter and bushing (to avoid abrasion). The PVC is to avoid the question of whether a clamp threaded into a conduit coupling is a proper bonding connection.

Option 3 is the same as Option 2, just skip the nipples, and the clamps can be installed normally (assuming you have access). As long as the panel is mounted directly to the siding, the small gap between the panel and siding, and between the siding and the air barrier envelope of the building, is generally ignored. So the NM cable is considered to be only indoors or in the panel, with no violation for running it through a wet location.

In all cases, the airspace inside the panel should not communicate with the interior airspace (to avoid condensation issues), so after all the cables are installed, each conduit/opening should be blocked with Duct Seal, say at the surface of the panel enclosure.

Cheers, Wayne
 

Xandrew245x

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Wayne,

Thank you so very much for the clear explanation. I knew that between the panel and the J-box had to be less than 24", but was unsure whether the LB also counted as an enclosure, I greatly appreciate the clarification on that.

I think I favor the J-box into the crawl space, since it will give easier access later on if needed.

I bought an 8x8x4 J-box, I have 15 12/2, 7 14/2 and 1 10/2 that will be wired into it. From box fill calculations there is plenty of room for this and room for additional circuits down the line. I'm going to tie the NM into the J-box with cable clamps and then run THHN wire from the J-box back to the panel. I'm going to label all the wires in the J-box as well as the panel.

Again I really appreciate the explanation, I've asked this question elsewhere and most people just tell me don't put the panel outside and don't give any useful information.
 

wwhitney

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For the box volume calculation, each of your cables will count twice, in that you have the cable coming in and the THWN going out. And the requirement is 2.0 in^3 for #14, 2.25 for #12, and 2.5 for #10. So you need:

2 * 2 * 7 * 2.0 + 2 * 2 * 15 * 2.25 + (2 * 2 + 1) * 2.5 = 203.5 in^3

where the last +1 is the allowance for the EGCs. So 8x8x4 is big enough, but I expect this is a situation where going bigger will make thing easier for your to work on. I suggest a 12x12x4. Possibly a metal box with knockouts and a grounding bar. If you stick with 2 equal cables per knockout and 2 equal sized EGCs per grounding bar hole, you'll need 13 KOs and 13 or 14 spaces on the grounding bar (depending on whether #10s can be doubled, not sure on that)

As for conduit size, 1-1/4" Schedule 40 would actually be sufficient (with the 60% fill allowance), but again larger will be easier so I'd suggest at least 1-1/2", with 2" being preferable.

Cheers, Wayne
 

Xandrew245x

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Wayne,

I'm really glad you explained that, I totally didn't factor the nm and thhn wire being counted as two. I was sizing off of the of the thhn coming on, so I'm really glad that was brought up.

I already have the conduit and connections made up, so 2" conduit is what I'm definitely going with.

With the 8x8 box, it looks like I would have room for 5 additional 12/2 circuits if needed. We're rewiring the whole house, and that's how many circuits I have total for all the runs and appliances. I might look into a 12x12, but I think the 8x8 would be sufficient. I could always add another J-box later on if it was direly needed.
 

wwhitney

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I've not made up a junction box like you are describing, but I strongly expect that if you use 8x8x4 you'll be unhappy getting everything to fit at all neatly, even though the calculation says it's OK. So I strongly suggest you go with at least 12x12x4.

Cheers, Wayne
 

wwhitney

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P.S. On the THWN side of things, you will need to comply with NEC 200.4(B) in each enclosure (junction box and panel). The NM cable takes care of it via the cable sheath.

Cheers, Wayne

200.4(B) Multiple Circuits. Where more than one neutral conductor associated with different circuits is in an enclosure, grounded circuit conductors of each circuit shall be identified or grouped to correspond with the ungrounded circuit conductor(s) by wire markers, cable ties, or similar means in at least one location within the enclosure.
 

Xandrew245x

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Thanks Wayne, I think you're probably right about it being a tight fit. I'm going to return the 8x8 and get the 12x12 to be safe.

On 200.4(B) if I'm understanding this correctly, each set of THWN has to be bundled together in some way once it enters the panel. They sell a three wire THWN wire that is braided together, would that be sufficient since they are clearly bundled together?

Thanks.
 

wwhitney

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200.4(B) applies to the junction box as well. I guess there you could argue that you can trace a wire to its splice, trace that to the NM, jump over to the other color, and trace that back. So maybe that would suffice, but I'd be inclined to associate the THWN more directly in the junction box. A double 2 port Wago Lever Nut, stacked back to back, would be a nice way to do the splices and would handle the association, but I don't think they make a mounting plate that would hold two 2-ports together back to back.

As to braiding, braided black/white would seem to me like it would comply with 200.4(B), although I claim no particular expertise at interpreting that language. You only need one EGC running from the panel to the junction box, a #10, as that is your largest EGC size on the NM side. So I do recommend getting an EGC bar and mounting it in your junction box (and if you use a metal box, that would be a good way to bond the box).

Cheers, Wayne
 

Xandrew245x

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Thank you again, you have definitely got me going in the right direction. I am going to get a bigger box and mount a ground terminal in it, and run one ground back to the panel (#10)

I had planned to use the two port wagos for my connections, could I simply stack them and tape or zip tie them together, then put a label on them? I would also label them back in the panel too.

Want to get this right the first time.
 

Reach4

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Wire markers and cable ties are cheap and easy.
 

wwhitney

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Sure, either cable ties or labels would suffice.

If you wanted to go overboard, you could put DIN rails on the back of the box, then use WAGO 221-500 mounting plates to hold (4) 2 port WAGOs each, in two groups of two, and secure the mounting plates to the DIN rails. The grouping would be providing by adjacency of Lever Nuts.

If this is new construction, you could use UF homeruns and not splice in the junction box at all. Its purpose would just be for securing all the cables. You'd have to check the conduit fill based on the cable diameter; 2" might not be enough. But UF is a pain to strip.

Or if you used a nipple out the back of the box and could get that to a junction box in the crawl space without burying any LBs and without exceeding 24", then you could do the same in NM cable.

Cheers, Wayne
 

Norcal01

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One problem is that NM cable "Romex®" is for dry locations only, any conduit outdoors is a wet location, so it either has to be brought into the back of the panel, or changed to a wiring method that is permitted in wet/damp locations, NM cable in a short length of conduit outdoors is not permitted.
 
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