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Background

Both the houses I deal with (which are quite far apart btw) are in need of panelboard reworks:

  • One still has the original fusebox, never mind that the main disconnect is basically at the 6'7" Code maximum, rendering it unreachable by people who don't have the luxury of finding it at eye level.
  • The other has a QO panel...in the master bathroom. What a waste of a QO! (Thankfully, AFAICT, the thing is still functional, but I want it out of its improper location before that statement becomes false.)

As a result, I have been making plans to rework the service and protection hardware for both houses.

The problem at hand

Considering that I want this to be the first and last time that anyone will ever have to do this to either house in question, being stingy with panelboard slots is penny-wise and ton-foolish. Also, in 2008, the NEC lifted the 42 slot limit on branch circuit (lighting and appliance) panelboards, and both AHJs have adopted the 2014 NEC, so that this limit is not a problem for me.

However, the light-duty panelboard manufacturers have been rather slow to catch up:

  • Square-D HOM is only available up to 42 slots, tops; the same is true for GE THQL, as well as the GE A-Series and Eaton Pow-R-Line commercial panelboards
  • Square-D QO loadcenters only go up to 42 slots as well save for a single 60 slot 200A offering (that costs almost as much as a NQ interior!); larger needs are shunted to the Square-D NQ line, which is available up to 84 slots and takes QO(B) breakers, but puts you squarely into having to order and spec a commercial panelboard (which is a fair bit more work) and also forces you to go to 20" width for upwards of 42 slots (with its attendant framing issues)
  • Siemens PL and ES loadcenters both go up to 54 slots (the same is true for distributor merchandised Revised P1 panelboards btw despite bigger Revised P1 interiors being available from the factory, up to 66 slots)
  • Eaton BR and CH loadcenters are both available up to 60 slots, which is the best I've seen so far from a light-duty loadcenter.

Of course, a subpanel with feeder breaker is an option for expansion, but this can be limiting as some light-duty loadcenters cannot feed a feeder as large as their main breaker/bus ampacity due to breaker availability/frame size limitations while those that can require a doublewide feeder breaker to do so:

  • Eaton CH breakers only go up to 150A (there was a CH2200, but it was discontinued)
  • GE THQLs have the 4-slot (apparently) TQDL line for ampacities up to at least 200A (although it's not listed in their catalog...)
  • QO and HOM breakers go up to 200A but at the cost of 2 extra slots over a regular 2 pole breaker for 150-200A.
  • The Eaton BR line has the BJ series double-size two pole breakers for ampacities from 125-225A
  • Likewise, Siemens QPs use double-size type QN breakers for 150-200A.

Considering that breakers can't be paralleled unless it's the factory's fault (240.8) -- this means that feeding a 400A subpanel off a 400A main panel is impossible. However, subfeed lugs don't fall under 240.8 as they don't provide overcurrent protection. While a single subfeed lug set is limited to 225A for all light-duty panelboard lines save for the CH which only provides 125A, we're into fat enough wiring here that parallel wires are permitted by 310.10(H).

This allows us to effectively implement feed-through lugs using one or more sets of subfeed lugs in the first interior and feedthrough conductors connecting the first interior to the main lugs in the second, even though light-duty loadcenters don't provide a true feedthrough lug option unlike their heavier-duty panelboard brethren. With this, we can then get as many slots as we wish with the ampacity we're after, all controlled by a single main disconnect.

The bottom line

Am I correct that Code allows you to use sufficiently sized feed-through or sub-feed lugs and wiring to "daisy chain" as many panelboard interiors together as you wish to make a single super-panelboard, spread out over N cabinets that are connected via an auxiliary gutter system or via conduits? Or is there some Code clause that'd trip me up if I tried this? (I'm not concerning myself with cost or physical space at this point in the design, simply safety and Code-compliance.)

Furthermore, if that is true, where is the neutral-to-ground bond performed in such a configuration? Do you just pick a cabinet and bond it there, and then pull the bonds on the rest of the panelboards, even though they technically are not really subpanels as there is no feeder to be found in this configuration? Or should the neutral-ground bonds be left in all the panelboard interiors involved? Could I even pull all the neutral-ground bonds and install a distribution block in the auxiliary gutter to make the neutral-ground connection at?

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    Talk to people with 400A service, typically in all electric homes in the snowbelt, many have two 200A main panels side by side fed straight off the meter. No problem if you want 84 or 120 space. – Harper Jul 9 '17 at 6:46
  • @Harper -- I've seen those configurations before while touring homes, and I'm personally not a fan. You wind up with two main disconnects, a load-balancing problem, and a neutral return system that's split in half effectively, creating more potential for screwups than a daisy-chained configuration like what I'm asking about here. (The only reason those split-service-hardware configurations exist is because the builder couldn't get their hands on 400A hardware, I reckon.) – ThreePhaseEel Jul 9 '17 at 14:11
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    Actually, we do this all the time in industrial and commercial settings with distribution panels for lighting or power. Multiple panels side-by-side nippled together fed from a trough above the panels. Services are no different. See below. 😊 – ArchonOSX Jul 9 '17 at 18:49
  • Why not split it after a single, fused, 400A disconnect? – Mazura Jul 9 '17 at 20:58
  • @Mazura -- don't those messy creatures called the feeder tap rules then come into play in your proposal? Also, call me weird, but I don't like fuses -- and you can't exactly get 400A fuses off the shelf from the borgs, no? – ThreePhaseEel Jul 9 '17 at 21:12
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Am I correct that Code allows you to use sufficiently sized feed-through or sub-feed lugs and wiring to "daisy chain" as many panelboard interiors together as you wish to make a single super-panelboard, spread out over N cabinets that are connected via an auxiliary gutter system or via conduits.

Short answer to your long question: Yes, except that you have to be able to shut down the entire service with six motions of the hand, so maximum six mains or disconnects.

So you can have a hundred cabinets as long as there are only six disconnects for the entire service.

230.71 Maximum Number of Disconnects.

(A) General. The service disconnecting means for each service permitted by 230.2, or for each set of service-entrance conductors permitted by 230.40, Exception No. 1, 3, 4, or 5, shall consist of not more than six switches or sets of circuit breakers, or a combination of not more than six switches and sets of circuit breakers, mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be not more than six sets of disconnects per service grouped in any one location.

Your other question about bonding the neutral and the ground: The service is one physical location. So, if you have six panels or disconnects in that location there they should all be bonded. They are all the service, none of them would be considered sub-panels.

Good luck!

  • Yes, if they're in the same location. But here then, one of the house's LCs is going to be a sub panel, no? Unless the question ( / answer) is, how do I double tap a meter and run it to another structure ... – Mazura Jul 9 '17 at 19:11
  • @Mazura don't quite get what you are saying. Don't know what an LC is. You can't double tap a meter but you can do a feed through panel or a trough with taps. – ArchonOSX Jul 9 '17 at 19:28
  • LC = load center (panel). What I mean is, one of them is going to (must?) be a sub if it's feed off a breaker in a LC from the other house, unless you pull some wire directly from the meter to the other structure. OP's post is kinda confusing: asks, Is this OK?, instead of, How do I maintain a single 400A service while splitting it to two structures on the same property? (with non-industrial sized equipment and a single LC in each house? ... you don't.) – Mazura Jul 9 '17 at 19:49
  • Hmmm yeah I am not getting where he says the two houses in question are actually on the same property. Last I knew, utilities will only allow one service per property no matter how big. Still, all you have to do is install a trough to feed both panels. – ArchonOSX Jul 9 '17 at 20:45
  • @ArchonOSX -- they're two different properties with similar troubles ;) you'd need a full-size transmission main if you wanted to connect the two LOL – ThreePhaseEel Jul 9 '17 at 21:09
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I am only answering this because I am familiar with @ThreePhaseEel and @Harper's experience and abilities. So if you are reading this and are more or less an amature please disregard.

The problem is when we talk about residential it's usually everything 200A and lower. Therefore when we talk about dwelling units we call them Panels but they are truly loadcenters. When we begin to talk about 400A equipment we really begin to move over to commercial type construction.

I am not sure if they manufacture a true Loadcenter with a 400A MCB so you would automatically be talking about a 400A Panelboard construction. Either way you could order a 400A MCB with 400A feed through lugs and attach it to a second or even a third 400A MLO. When I say order I mean you would have to go through a wholesaler and have the Panel special ordered. I doubt you could find one in stock. You noted a 225A by Eaton and if you keep it under that or 200A and are just looking for breaker space. You can probably use Loadcenter construction but I am pretty sure you would still have to order it from a wholesaler.

This is done all the time in commercial construction. Particularly in large office or multi story buildings. You could even reduce the feed to the second panel, but you have to follow the tap rule requirements given in the NEC. If you choose to do that be ready and have load calcs ready for the AHJ.

So yes I have done it on some large Ranches and a few large Dwellings, actually three phase, but because of utility distribution in these areas it is generally a delta with a high leg. What usually kicks it in the butt is the cost effectiveness of the main equipment. So if that becomes a problem then we go with @Harpers suggestion which is a more competitive way of installing it and we use NEC Article 220 to calculate and distribute the load.

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