I'm adding a workshop needing its own 200A panel, and power company (TEP) is requiring me to move the service entrance from the house to the workshop (and upgrade to 400A panel) the house is to be backfed as a feeder 100' to its original (old) 200A panel, moving the entrance from the overhead meter to from below (see pic). The bond between neutral and ground will be removed in the house panel. the entrance feeder will carry 4 wires in a 2.5" conduit (Al250 Al250 Al4/0 and a #6cu ground wire). ground rods will be kept at the house and tied to the incoming #6 ground (there is also a big ground rod at the shop where it is tied to the neutral leg) I finally Found an affordable box approved for 400A by TEP on a waiver, don't know why they are so expensive...

There is a bunch of space in the old 200a house box behind the breakers (the box is 5.5" thick, and the insulators just stand off 1.5" all the way up to the main breakers on top. Can I run the new entrance below the breakers in the box straight up to where they tie to the lugs? (ive never seen this on any other box... and I plan to run in the gutters as normal otherwise) ![old house panel with entrance moved to below

enter image description here

Does anyone see anything wrong with my plan (I wont remove the N-G tie till the day service is cut off)?

Edit: Proposed new 400amp all-in-one meter panel Is a Siemens MC0816B1400SC . Old panel is something from GE. Shop will need 200a, and Tucson Electric Power directed us to drop the service into the shop and customer (me) run back feeder to power the house box. Rationale was, they didn't have any more capacity on the pole at the house and the shop is closer to another pole (even though its just 100'). I had proposed the update recommended (320 service to house with sub at shop, they said "nope, no more capacity")

Here are the current knockouts on the existing House 200A box...I cant find the label on it with the make and model. I do have some moving around to do for a couple of the existing conduits -out- to make room for the giant feeder into the center. [Original plan3

And here is pics of the completed install after inspection: The three supply Hots and neutral go through the center section under the breakers up to the home owners meter. enter image description here

  • TEP = Tucson Electric Power I take it? Also, can you give us a make/model number for your proposed metering hardware please? Commented Aug 14, 2020 at 1:11
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    If the dots are your idea of phase, both breakers in the same horizontal row will be on the same phase. Commented Aug 14, 2020 at 2:40
  • @Markf -- can you confirm that your utility is Tucson Electric Power please? Also, can you get us photos of the labeling on your existing breaker box, or at least a photo of the KOs at the bottom? Commented Aug 15, 2020 at 21:32
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    Hi. Just saw your edit - it looks like you created a new account to do the edit with. Click here to fill out the form to get them merged to make your life easier.
    – FreeMan
    Commented Aug 17, 2020 at 16:10

3 Answers 3


Yes you can bottom feed the old panel, I have even seen panels put in upside down to save 2’ of wire., it looks like you have a mix of breakers the inspector may hit you on that. I might start moving neutrals and grounds around ahead of time it looks like neutral on the right and ground on the left and having that done ahead of time may help with the inspector.

  • What am I missing here? Why not go with a class 320 service? No changes needed to main panel. No need for an expensive 400 amp main panel. Just upgrade the meter base and run a circuit to the shop. I may be missing something obvious, but I don't know what that might be. Commented Aug 14, 2020 at 1:27
  • George I kind of agree but I have installed true 400 amp meters and CT meters, the utility is requiring the move and we don’t know it may be a 30/40 panel or 320 I have worked in 3 counties regularly in Oregon and the different utilities had different rules even different for rural vs suburban In the same county true 400 ct rural and 30/40 or 320 suburban unless commercial. Crazy but that may be what the op is having to deal with.
    – Ed Beal
    Commented Aug 14, 2020 at 4:48
  • It looks like the OP was edited to include more information which answers my question/comment. Thanks for the comment. I've installed a couple of class 320 MBs and it was no issue at all. In both cases the POCO was Puget Sound Energy. Commented Aug 14, 2020 at 13:40
  • @george Anderson did you see that they are bringing back reciprocal licensing for Or/Wa General journeys I saw the temp law passed this week in Or.
    – Ed Beal
    Commented Aug 14, 2020 at 14:03

400A boxes

400A panels are expensive because nobody does that. The normal thing to do with a 400A meter is immediately split it to two 200A main panels, just ordinary common-as-dirt main panels, nothing fancy at all. In fact, ordinary/common "class 320" (read: 400A) meter pans provide for two 4/0-sized lugs per phase. That's not for paralleling: That's for splitting to two different main panels. You couldn't attach a single 400A panel if you wanted to, because the lugs won't take a 500 kcmil conductor, and they're not for paralleling.

For some reason, some people with a certain level of electrical knowledge get fixated on doing it some other way (sometimes they cannot believe you can just split to two main panels like that)... and they always wind up with an expensive adventure.

Now, given your requirements, what I would do is (gosh) split to two 200A main panels. One of the panels would have "Thru Lugs". The other would be the normal shop panel. So one-a these, and one-a these, coming off any common 320-class meter socket. Together under $300. You can spend a little more and get the better QO, Siemens, CH etc. I'm presuming outdoor for NEC 2020.

Anyway, feed the house off the panel with the thru-lugs. It's beholden to the 200A main breaker in that panel, so the run to the house is protected. It has 8 spaces for if you want to tap anything locally off that side of the service. The 30-space is for the workshop. I know it's smallish, but feel free to get a 40.

that was easy :)

The neutral bars (plural)

On your original panel, both sides are intended as neutral bars. They have several features that ground bars don't have. The panel provides enough neutral lugs for every space in the panel to be a "double-stuff" breaker feeding 2 independent circuits. You're nowhere near even half that, so you have the option to spin off one neutral bar to make it a ground bar.

However, that's not your only option. The common way to do that is to buy accessory ground bars for the panel ($8 or so). These bolt to the metal frame of the panel. You may find that more convenient if some neutrals or grounds are too short. You can get those (I would get 2), move the grounds to it at your leisure, and then simply remove the N-G boding screw or strap on Upgrade Day. I don't see one, which is a bit odd.

Routing the cables

Your proposal for cable routing (coming in the bottom when it came in the top/back before) seems perfectly fine to me. It's clear from your photo that the panel builder left you plenty of wire bending space for that purpose.

Make sure to put a knockout cover on any abandoned holes.

  • Since everything is bottom fed there is no need to add an additional ground buss when there is a perfectly good one already there. Not sure why you go off on a silly 400 main rant when the op has 200/200 in the question , the meter has to be comparable and that is controlled by the utility, they don’t like it they won’t hook up to it.
    – Ed Beal
    Commented Aug 14, 2020 at 14:00
  • @EdBeal Read Comment 2 of the question re: box type. My "ground bar" comment was for wire length. Commented Aug 14, 2020 at 14:59
  • With everything entering from the bottom there should be enough it is not like mr snippy was in there it looks like there is more than enough to neatly change using the existing busses.
    – Ed Beal
    Commented Aug 14, 2020 at 15:09
  • @EdBeal Yeah, I'd tend to agree in this box... but there might always be that one. Also I don't trust the way this box has only ten 120V circuits, how can a whole house get by with so few? I fear if they ever do a kitchen remodel, suddenly this box will be full of neutral-hungry double-stuffs... Commented Aug 14, 2020 at 15:48
  • I guess maybe I have wired two many houses but 10 is appropriate for a nice sized home. I can’t tell you the number of homes I have seen with only 3 or 4 and that many are mandated today + the standard lighting and receptacle. I guess that is the difference in reality of doing the job and a an ideal idea.
    – Ed Beal
    Commented Aug 14, 2020 at 16:08

Penny-pinching now puts you in a bind later

There are two main problems with the setup you propose. First off, it relies on the rule of six as the meter-main you propose requires two separate breakers to be thrown to disconnect all the power; this is an issue because that rule is being curtailed in the 2020 NEC to prohibit a single panelboard enclosure from having more than one main disconnect. (Assuming TEP stands for Tucson Electric Power, then your power company's rules, as written, also require a single main disconnecting means.)

Furthermore, and more importantly, it limits you to only ever being able to provide 200A to the house, as NEC 225.30 says that you cannot have more than one feeder to a structure, and the exceptions don't apply to your situation by and large:

225.30 Number of Supplies. A building or other structure that is served by a branch circuit or feeder on the load side of a service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.

Where a branch circuit or feeder originates in these additional buildings or other structures, only one feeder or branch circuit shall be permitted to supply power back to the original building or structure, unless permitted in 225.30(A) through (E).

As a result of this, you're much better off saving up a couple extra grand now for a single-disconnect 400A meter-loadcenter, such as the Siemens MC2442B1400SD(S), than backing yourself into a corner with a "rule of six" panel that won't let you expand the feeder to the house down the road. Imagine how frustrating it'd be to have a 400A service, but not be able to put in a Supercharger for your new Tesla because the feeder to the house can't go any higher than 200A.

Sizing the new conduit in keeping with that theme...

To keep with the theme of providing space for expansion, we will need to use a larger conduit from the new service location to the house. A 3" PVC conduit provides plenty of space, even for a 400A feeder (6x 250kcmil Al with a 2AWG bare copper ground, which takes up 1358mm2 of space, compared to the 1660mm2 available in a schedule 80 PVC conduit of that size); it will likely require a 3" to 2.5" reducer to fit your existing panel, but that's generally a tolerable state of affairs since going to 400A at the house would require you to add a tap box and a second 200A loadcenter, at a minimum.

As to routing the new feeder wires into the loadcenter...

You'll have to use the side gutters in your existing loadcenter for routing the new feeder wires from the bottom to the top, as your illustration depicts. However, both of the existing side bars in your current breaker box are neutrals, so you'll have to get an ECGB201/202 ground bar kit for your existing panel (presuming that it's a Siemens panel, that is) and fit it, then move the existing grounding wires to it.

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