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I have a weird setup that I'm trying to configure, but I'm only 90% certain of my logic (and with electrical items I want to be 100%).

I have a new 400A meter/main combo unit with 1 built-in (supplied) 200A breaker to provide power to a 200A subfeed panel.

The same main box has spaces for up to 8 additional circuits for either additional subfeed panels (high current) or regular circuits (15A-40A). Here's the Siemens schematic.

The subfeed panel I'm using comes equipped from Siemens with a 225A main shutoff. Siemens schematic

My question is this: Can I leave the existing 225A main shutoff at the subfeed panel even though the max current for the upstream feed is 200A?

Basically, I bought the panel that has larger capacity and it came with a larger main (225A); however, the circuits in use are spec'd for 200A and that's why the upstream (from the meter/panel main) is 200A.

My thought is, just as with everything else, the smallest number will win, but the 225A physical shutoff (while not even strictly necessary because there's a physical upstream shutoff) provides an easier way to kill the power locally vs going outside.

Anything wrong with my logic/plan?

Thanks!

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2 Answers 2

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You are fine.

The 200 amp breaker in the main panel will protect the wires leading to the sub. The main breaker in the sub is not strictly necessary, except as a local shutoff. You could as easily use a sub designed with no main, feeding directly to the bus bars.

The only requirement in this context is that the feeder breaker be sized to protect the feed wires and the sub panel itself.

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    Yup we do it all the time I regularly but in sub panels at 100 fed by a 60 or 80 amp breaker from the main. The wire size is based on the breaker in the main panel+
    – Ed Beal
    Commented Feb 14, 2019 at 19:39
  • You could do that but why? If there is an overcurrent or short you could be forced to go back to the main panel to reset, instead of resetting the local breaker. The building I'm in (20 units) with each having a two-fuse service disconnect in the meter room. Over the years electricians have installed the standard Seimens panels that come with main 100 amp disconnects. A few times they've blown the 60 amp fuses in the (locked) meter room, rather than trip the tenants service main. A pain.
    – Chris Taylor
    Commented Feb 15, 2019 at 3:37
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    Because the custom order came with a pre-set 225A shutoff in the panel and I don't want to dork around with it. Plus, the main panel is rate limited to 200A (can't support a 225A subfeed) anyway, so worst case I'd remove the subfeed's breaker and have no shut off there OR I'd have to fork out $ to buy a 200A shutoff and then basically have no gain. In addition, technically, by having another breaker in the loop I can increase the amount of over current (surge) that can be absorbed before damaging actual lighting/receptacle devices.
    – Nick
    Commented Feb 15, 2019 at 20:19
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You are correct that you don't even need a main breaker in this subpanel. You might even consider a main lug panel, particularly if that will buy some more spaces for the same money. Spaces are golden. The biggest regret we see on this forum is someone scrimping a few pennies by getting a smaller panel that is only big enough for the loads they foresee right then. Then, inevitably, along comes the hot tub, dust collector, garage freezer he doesn't want on GFCI, on-demand water heater, electric car, etc.

It is vital that the upstream breaker be sized to protect the wires to the subpanel. Other than that, the subpanel's main breaker size simply does not matter.

  • if the subpanel's main breaker is larger than the supply breaker, it has no effect.
  • if smaller than the supply breaker, the subpanel's main breaker protects the subpanel.
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  • Haha. Actually this was a custom order (took Siemens 5 weeks to build/ship). It has room for 54 spaces and 80 circuits (if the slim breakers are used). I paid quite a bit extra for this one. As a side note, the wires are 4/0 copper from the main panel to the subfeed panel.
    – Nick
    Commented Feb 15, 2019 at 20:17
  • 54 and a sub to boot! I think you're ok then :)
    – Harper - Reinstate Monica
    Commented Feb 15, 2019 at 20:21
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    Actually, it's a 400A meter/main combo feeding 3 subfeed panels: 200A, and 2x 125A. the 200A is the 54 spaces 80 circuits, the two 125A are 30 spaces 30 circuits. all in all i have 'nuf space :)
    – Nick
    Commented Feb 18, 2019 at 19:41

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