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I am considering purchasing a 225-amp Siemens panel, to do a replacement of my main load center. But I wish to replace its 225-amp main breaker with a 200-amp main breaker. I am wondering if this is code-compliant ? I believe it is, but a guy at a supply house told me that it is not.

By explanation, I wish to use the 225-amp panel because:

  1. It is very large, 42-spaces/64-circuits, and lots of wire-bending space.
  2. Having the heavier busbars maybe useful when adding solar.
  3. I'll have the option of upgrading to 225-amp service in the future.

But, for now, I want to stick with 200-amp service.

The cut-sheet for the panel clearly shows the 200-amp main breaker as an option (see "Accessories" at bottom). I think the supply-house guy is either a dope, or confused, but I want to check.

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    Did the supply-house dude just say that it was "against code", or did he point at a specific Code section?
    – ThreePhaseEel
    Dec 18, 2021 at 19:32
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    No specific code section. Just "against code" and a lecture about how I would be in trouble if there were a fire or something. I'm gonna go with ... dope .
    – RustyShackleford
    Dec 18, 2021 at 23:18

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Supply-house dude is very confused

What you describe, namely taking a convertible main breaker panel and replacing the factory fitted main with a lower amperage main breaker of the correct type, is perfectly fine. In fact, the panel's label not only calls out the MBK200A kit you'd need to use for this conversion in its table of permitted main lug/main breaker kits, it also calls out the EQ8695 (which is the UL type for the MBK200A as per the current Siemens catalog) as a permitted main breaker in the label's series rating table.

In fact, what you are doing by downbreakering the main panel may even be required by NEC 705.12(B)(2)(3) in order to protect the panel busbars from overloads when distributed generation is interconnected on the load side of the service disconnecting means. So, the supply-house dude is just plain wrong on such downbreakering being prohibited by the NEC.

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  • Your second paragraph is talking about (among other things) the situation where one attaches a solar inverter via a circuit breaker (as opposed to taps on the line side of the main breaker), and fails to put that breaker at the far end of the breaker column from the main breaker.
    – RustyShackleford
    Dec 18, 2021 at 23:21
  • I attached using line-side taps. One reason was that my panel is chock-a-block full, perhaps the main reason I want to replace my panel. Even if I had the room, I'd have an issue with being unable to interlock my generator breaker with both the main breaker AND the solar breaker. Not being to interlock the latter would mean my generator could get into a tussle with the solar inverter. No bueno.
    – RustyShackleford
    Dec 18, 2021 at 23:23
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    "my generator could get into a tussle with the solar inverter" LOL no chance of that. The UL 1741 rated inverter is looking for much cleaner power than you'll ever get from a clunky mechanical generator. However, a grid forming inverter connected to a battery is designed to fool a UL 1741 inverter into powering up, and will capture the solar panels' output into the battery. That's the whole point of it.
    – Harper - Reinstate Monica
    Dec 19, 2021 at 7:25
  • I currently have my main breaker interlocked with a breaker connected to a generator inlet; my solar inverter is connected to the line-side of the main breaker with taps. You saying it'd be ok to attach the solar inverter to another breaker, and if I fail to turn that one off, when switching the interlock to generator mode, it's cool ? BTW, right now my "generator" is a 1kW/120vac inverter connected to our EV's 12v system; the hot is connected to both hots of the generator inlet. So unlikely the solar inverter will think that zero volts across what should be 240v is a valid grid signal.
    – RustyShackleford
    Dec 19, 2021 at 19:23
  • But I hate to risk damaging equipment, or worse. Maybe this is a little screwy, but ... how about connecting the solar inverter to the main panel via the generatpr inlet box (with a short cord and a 14-30 plug). Swap the plug out when you want to attach the generaator.
    – RustyShackleford
    Dec 20, 2021 at 3:46
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Panel busing and main breaker are not the same thing

I think you are assuming that any panel with a factory X amp breaker also has an X amp bus. However the manufacturers don't want to make a different bus assembly for each panel type. Honestly until now I had simply presumed most 200A panels have 225A busing internally. You have to check their labeling and specifications case by case.

Remember in NEC 2020 territory you need a meter-main, meaning a "main bus" panel will suffice.

So you are fine, just as the cut-sheet says. If someone is against buying a 225A panel and changing to a 200A breaker -- it's probably because it's a costly way to do that thing as compared to finding a "200A main breaker" panel that happens to have a 225A bus.

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  • Hmm, I'd be happier with a slightly smaller 200amp panel, perhaps a 40-space/60-circuit.. You suggesting it might be legal to put a 225-amp main breaker on that one ? They do say you can convert to a 225-amp main lug. cache.industry.siemens.com/dl/files/410/109792410/att_1051522/…
    – RustyShackleford
    Dec 18, 2021 at 23:28
  • I do not understand your second paragraph. You mean if I have a meter base with a shutoff, I can use a main-lug panel ?
    – RustyShackleford
    Dec 18, 2021 at 23:30
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    @RustyShackleford I can't see any evidence that one has a 225A bus. The biggest clue we have is the list of approved retrofit main breakers: the largest is 200A. The label on the panel would say for sure.
    – Harper - Reinstate Monica
    Dec 18, 2021 at 23:58

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