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I had a 100A service (MSP) with a 100A sub panel. I do not know the feeder size to the subpanel but it supports 100A but definitely not 200A.

Last year, the service (and MSP) got upgraded to 200A. The feeder to the sub panel of course stayed protected with a 100A beaker.

Last month, also the sub panel got upgraded to a 200A version. But since the feeder is still 100A, the sub panel stays a 100A panel, even though the panel itself would support 200A. The 200A main breaker got removed from the sub panel. The whole feeder and sub panel is protected by the 100A breaker in the MSP.

Can I put the 200A main breaker into the sub panel and use it as a “switch”? I would like to be able to turn off the sub panel without having to go outside to the MSP. Note: I would not operate this “switch” often; only very occasionally when I do work in the sub-panel.

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    Essentially using it as a local main breaker. Hm. It would work, and the 100A outgoing breaker would mean it was never used except as a switch, but if I were writing code I'd worry about it misleading someone into trying to draw too much from the subpanel. Less "can I" than "may I".
    – keshlam
    Dec 2, 2023 at 8:56
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    Read the documentation or contact the maker of the specific breaker to determine if frequent manual operation will cause premature failure. If it's designed to do what you want there is nothing wrong with it. You could feed the panel with a #10 cable and a 30A breaker at the source, and you won't find a 30A main breaker to use for local switching. You have to use a bigger one. Similarly you could use an external DPDT switch ($$$) and that's like using a much--more-than-200A main breaker. Waste of money. You could upgrade the cable later and you'll be set to go.
    – jay613
    Dec 2, 2023 at 9:24
  • Most question answers suggest using it as the required disconnect. I think most main breakers are not designed to be used as an often used switch, but the branch circuit breakers are. If the circuits in the sub panel can be out for some time, I imagine if it does go bad it won't matter as much as the main house breaker.
    – crip659
    Dec 2, 2023 at 11:20
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    Maybe edit the question. The word "switch" tends to mean a device to turn on/off often, like a light switch. I think you mean it to use as a main breaker that is used once in a blue moon to do rare work in the panel. If so that is perfect.
    – crip659
    Dec 2, 2023 at 13:18

3 Answers 3

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There are two ways a breaker (main or branch) can be used as a "switch".

  • Occasional

For this, any breaker will work just fine. There are plenty of times where the main breaker on a panel (whether technically main panel or subpanel is irrelevant) is turned off in order to safely work inside the panel. Some work can be done inside the panel without turning off the main breaker, but how much depends on the type of work, your skill level and safety concerns.

  • Frequent

If you plan to turn a breaker on/off frequently, e.g., daily, then it should be switch duty rated, or SWD. This is typically on branch breakers, not main breakers, and often only on smaller ones. For example, according to manufacturer catalogs, the Eaton CH 15A - 20A single pole breakers, the Square D QO 15A - 20A single pole breakers and the Square D Homeline 15A - 20A breakers are all SWD rated. That doesn't mean you won't find some larger breakers that are SWD rated, but it gives you some idea of what look for. The larger the load, the more wear and tear involved and concerns about reliability with frequent switching.

So if the goal is "occasionally work on the panel without having to to the main panel to turn the subpanel off and back on" then yes, a main breaker (any size >= 100A) in the subpanel will do just fine. If the goal is "turn everything controlled by the subpanel on/off every day using one big switch" then this is not a good idea.

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It depends on whether or not the breaker is rated as a switch. You should be able to find out in the paperwork that came with the panel.

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    Or Google the model number Dec 2, 2023 at 22:23
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You can use an over-rated main breaker as a switch.

Maybe I'm just being overly cautious, but it seems to me there's something missing here. There really isn't any reason to remove the main breaker in the subpanel to begin with, but if it was just taken out because it wasn't needed then you can certainly put it back.

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  • Wonderful, thank you! The electrician removed it (and actually took it with him). I later figured out that this thing is quite expensive and demanded it back. I planned to upgrade the feeders to put it in again but it seems that’s not required.
    – divB
    Dec 3, 2023 at 7:09
  • A 200A main breaker by itself is on the order of $100, sometimes more depending on brand. A full 200A panel - including case, bus, main breaker, often extra branch breakers, etc. is often on the order of $150 - $200 and sometimes less. Parts > whole. Dec 3, 2023 at 17:14

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