200 amp service entrance to 200 amp sub panel?

Question

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

Answer 1

There are two approaches to your situation with powering the house:

• The conventional approach is to use a feeder-breaker 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 use subfeed lugs to feed the inside subpanel. 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 (if your conduit is plastic) 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; EMT or rigid metal is recommended, but PVC can be used if you're willing to toss the ground wire in there. 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 (if present/necessary) 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 (if necessary) 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 it's still going to be cheaper and easier most likely than the more typical approach in your case.

What you are trying to do 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. However, 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. This leaves the service equipment outside, and creates a lug-fed subpanel at the inside location, with the bonding screw/strap removed from the inside subpanel, of course.

The conventional approach

In the conventional approach, we use a 200A feeder breaker to create a separately switched 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. The wiring, of course, is the same as above, just with the breaker instead of the subfeed lug kit.

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.