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I have a 200 amp service entrance outdoor breaker box. I want to install an indoor breaker box with 200 amp service about 5' away so I can access breakers from inside the house. The actual wire run will be about 12' or less. Can I add a 200 amp indoor box and send 200 amps to it? I did an online load calculation of my appliances and it appears I could pull up to 125 amps. I'm not sure if this included wall outlets, lights, ceiling fans, etc. The kicker to this is would also want to have 100 amp service in my shop which is about a 120' run. Any guidance would be much appreciated. (recommended conductor sizes too) Thanks, Scott

  • What make and model is the outdoor box? Also, can you provide the square footage of your house, how many kitchen countertop circuits you have, and the nameplate rating of all your large/hardwired electrical appliances? – ThreePhaseEel Jul 30 '17 at 15:49
  • Both boxes (indoor and outdoor are GE 200 amp boxes) House sq. ft. 1650. I am restoring the old house I grew up in so circuit count is not complete. I have about half of the house rewired and want to transfer current to the indoor box so I can power the outlets and lights I have already installed. (Need some light other the my temp. shop lights) I thought that if I'm going to bring the power in to the new box, I may as well run the proper wire so I don't have to go back. (hence the 200 amp service) According to the online load calculator, I should end up needing a max. of 125-150 amp service. – Newland Jul 30 '17 at 16:21
  • Spare capacity is always good, I hope you keep that in mind when sizing your service panel. Will these 8 feet of wire be after the main breaker? Or before? – Harper Jul 30 '17 at 17:16
  • What's the exact model number on the outdoor box? – ThreePhaseEel Jul 30 '17 at 17:22
  • Harper - Indoor panel is basically one stud opening over from the outdoor panel. The only reason I called it 12' is I will be coming through the bottom of my outdoor panel, up between the studs, through the stud to top of the indoor panel and both are about 3' in height. The 12' is a worst case for bending etc. I will probably more along the lines of 9'-10'. – Newland Jul 30 '17 at 17:36
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There are two approaches to your situation with powering the house:

  • The conventional approach is to use a feeder and subpanel setup. This works, and is pretty much guaranteed to be accepted by your AHJ when done correctly, but has the disadvantage that it requires a big (200A) branch breaker in the outdoor panel, which can be problematic in some cases, such as yours.
  • The more streamlined albeit less conventional approach is to split the service equipment across multiple enclosures. This has some advantages (it's cheaper in your case for one) but could cause an inspector not used to seeing a "daisy-chain" of panelboards (this sort of feed-through configuration is much more common in commercial work than it is in residential) to complain even though it's Code-compliant.

What you'll want to install for both cases

Either way you go, you'll need to run four wires in conduit between the two panels. The hot and neutral wires will be 250kcmil aluminum, while the ground will be a 6AWG bare copper wire (this saves on conduit fill). The conduit will need to be 2" minimum with a 2.5" conduit preferred. (SE cable doesn't work as you'd need to go up to 350kcmil for that as NEC 338.10(B)(4) would leave you stuck with 60°C ampacities in that case and your lugs won't accept wire that fat.) In the indoor panel, the hot conductors land on the main lugs or main breaker there, while the neutral lands on the neutral lug and the ground lands on the ground lug. Outside, the neutral lands on an add-on neutral lug (a TNLK250) attached to the neutral bar and the ground lands on the ground bar.

Running this connection via the path that yields the shortest route with the fewest bends is wise, by the way. I would route out the back of the outdoor panel using a suitably sized (no shorter than six times the diameter of the conduit used) LB (a Crouse-Hinds LBNEC7 works, for instance), then make a straight shot into the interior panel from the LB if at all possible. Less wire, less pulling, less hassle.

The streamlined way

I'll start with the streamlined approach, since even with a bit of plan review and explanation, it's still going to be cheaper and easier most likely than the subpanel approach in your case.

What you are doing here is spreading the service equipment over multiple enclosures. This is typically done in commercial applications using what are known as feed-through lugs in commercial panelboards to feed a second panelboard directly from the busbars of the first without any intervening switch, fuse, or breaker, and also is usually only done when the enclosures are adjacent. However, your enclosures are close enough together that they might as well be adjacent, and while loadcenters don't have true feed-through lugs available, a set of suitably rated subfeed lugs can be used instead.

As to actually putting it together, you would use a set of THLK2200 subfeed lugs in the outdoor panel and attach the hot wires to the subfeed lugs, then leave the bonding jumper in the inside loadcenter. The "ground" wire becomes a redundant bonding jumper in this case, and neutrals for circuits originate at the loadcenter their corresponding hots originate at. The service disconnecting means is still outside, as it always was; however, both enclosures, taken together with the wiring and conduit connecting them, form the service equipment in this case.

The conventional approach

In the conventional approach, we use a 200A feeder breaker to create a true feeder and subpanel system here. The required breaker is a GE TQDL21200 (or equivalently a Midwest Electric CB2200B); however, they are relatively rare/hard-to-find. Thankfully, wiring this is the easy part once you have the breaker in hand: the hots outside land on the breaker lugs, and the system bonding jumper in the inside panel gets pulled, just like any other subpanel setup.

As to the shop feeder

Once you have the house out of the way, then we can talk about powering up the shop. Over 120', 1/0 AWG aluminum can be used either in the form of individual wires in Schedule 80 PVC or a four-wire type SE cable rated for direct burial. The ground wire in the feeder needs to be a minimum of 8AWG copper and a grounding electrode (ground rod) will need to be driven at the shop and connected to the shop subpanel by an 8AWG copper wire.

The outdoor panel will receive a THQL21100 feeder breaker and a TNLK20 neutral lug to accommodate this, while the shop will need its own subpanel with the bonding jumper pulled and the shop grounding electrode conductor landed on the ground bar in addition to the feeder ground. The feeder neutral lands on the neutral bar, while the feeder hots land on the line-side terminals of whatever the disconnecting means in that subpanel is -- it could be a main breaker or a backfed disconnecting device fitted with a hold-down kit. In the main panel, the shop feeder hots land on the lugs of the feeder breaker, while the shop feeder neutral lands on the added neutral lug, and the shop feeder ground lands on the ground bar as usual.

  • 3P - Would you mind repeating that.... I bow to you in awe realizing how much I have to learn. I'm going to have to read this a couple of times to get full apprehension before I can even think about responding. I can say I enjoyed the "unobtainium" description. I sure hope this doesn't make you want to kick me in the butt, but, what if I relocated my incoming service wire to go directly to the inside panel and then use the outside panel as a sub panel? After all, I am restoring the house and I currently have no sheetrock, insulation or siding completed. Would that route make things easier? – Newland Jul 31 '17 at 2:02
  • If you're relocating the service wire, then you might as well slap more panel hardware inside if you have the space to put it instead of having bits inside and bits outside. Does your locale have any requirements that force the service disconnect outside, though? – ThreePhaseEel Jul 31 '17 at 2:06
  • @Newland -- btw: is there a reason you went with the indoor panel you did instead of a 42slot model? (Sadly, GE doesn't make anything bigger than 42 slots even though Code has let you have more since 2008 -- its one of the reasons they're at the bottom of my list re: panelboard options.) – ThreePhaseEel Jul 31 '17 at 2:11
  • 3P - I'm only required to follow NEC 2014. (no adders). As far as the panel goes, it's probably the largest Home Depot had. (I normally get more than I need for future upgrades if necessary). I went with GE because it's a common name and I could use the same breakers for both. What's your preference? The inside box can be returned. I haven't wired anything in yet and I have no issue using a "better" brand if it's preferable. Didn't intent to relocate, but have the option to if needed. If relocated, I can only move a short distance to the new box. (wiring half complete with a few extra feet) – Newland Jul 31 '17 at 13:09
  • 3P - I just noticed I missed one of your questions. Your are correct that the shop service will be underground. – Newland Jul 31 '17 at 15:07

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