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I have a severely scary Stab-Lok panel that has no main breaker. The breakers spark and fall out when the panel is slightly wiggled. It's tiny and there's hardly any room to work, so I'm not about to screw around inside there while the mains are live. So, I need to have the electric company come out and pull the meter.

I figure while the meter is off, why not just replace the panel? So I bought a 200A load center with main breaker installed. My service is currently only 100A, but we plan on upgrading some time in the future (not sure how long it'll be). The main concern right now is to get the damned Stab-Lok panel out of here.

So, the question I have is, which is the best temporary route to take?

  1. Just connect the lines to the installed 200A main breaker.

  2. Remove the breaker and convert panel to main lug and connect directly (as the old one is now).

  3. Remove the installed breaker. And backfeed the panel through 100A breaker as specified in the wiring diagram. (But lose 4 spaces.)

Honestly, I'm strongly leaning towards #1. At least the panel will be protected and I'll be able to use the main breaker as a disconnect.

Thanks, Michael

BTW, the panel I bought was a Siemens P3040B1200CU and they don't make a 100A main breaker for it.

Update with photo: enter image description here

The Siemens panel I plan to use photo: enter image description here

  • Hello, and welcome to Home Improvement. Good question; keep 'em coming! (And, a picture of the scary panel would be fun, and perhaps informative.) – Daniel Griscom May 11 at 1:52
  • When you say your panel has "no main breaker", are you talking about a Rule of Six panel, with a breaker in the "top half" feeding the breakers in the "bottom half"? – ThreePhaseEel May 11 at 3:16
  • Also, do you have a full 14" between studs available for the new panel? The word "tiny" has me concerned that your new panel may not fit where you're trying to put it... – ThreePhaseEel May 11 at 3:17
  • Finally, photos of the old main panel would be helpful here :) – ThreePhaseEel May 11 at 3:19
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    A 30-space panel is never overkill. If anything, I was thinking it's a bit small. The reason is there are a bunch of things you haven't done because they've been out of the question because you haven't had the panel spaces. Now that you do, believe me, you'll fill 'em up! – Harper May 11 at 4:57
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1) can't happen without the power company's consent, and the meter pan and service drop up to the weatherhead must also be rated for 200A. If those aren't true, you can't do #1.

2) is out of the question. The old setup was legal because it was so small it qualified for the Rule of Six (six throws to turn off everything). And the maximum theoretical load, all circuits at redline, was 125A on one pole and 150A on the other. That is such a modest oversubscription that since the Rule of Six was allowed, a main breaker wasn't really needed. However, different deal on a modern 30-42 space panel with 200-400A of breakers provisioned on each pole. Besides, the Rule of Six is now outlawed! You must have a main breaker today.

That leaves #3, and I recommend switching panel brands to one where a 100A main breaker is readily available. Unless you plan to have a generator; in that case stay with Siemens but swap it out to a main-lug panel (why pay for the main breaker) and fit their generator interlock.

You can also backfeed this panel and ignore the main breaker, but I do not like panels where the main shutoff is not obvious. In an emergency, people don't rise to the occasion, they sink to the level of their training. In other words people get stupid in key moments. Someone frantically working in the dark is gonna grab the big handle and go THWOP. And he will expect the power to be off at that point. So if that does nothing and you have to shut off one of the regular breakers, well, that's just confusing...

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    As I mentioned this is only temporary, so I’m not too worried about someone else messing with the panel. I did decide on #3 though and leaving the main breaker in place. Thanks. – Michael May 11 at 17:40
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I would go with option #3, but leave the 200A main fitted

Personally, given your situation, I would go with option #3; you only actually lose two spaces (instead of the four you think you do) by doing this, and you get properly sized protection as a result. (The lack of downbreaker kits for 200A panels is a major downside of the Siemens loadcenter line, I find, even.)

However, you can leave the panel in its main breaker configuration even though you are fitting a backfed main. This saves you the time and cost of fitting a main lug kit and matching filler plate to your replacement panel, and the unused breaker is not an issue from a Code standpoint as long as it's marked on the directory as unused, with the real main marked accordingly.

  • I thought the main breaker was to protect the panel, not the service lines? Is it for both? Because as it is now, there's nothing! – Michael May 11 at 3:58
  • Also... I was told it was not safe to leave the main breaker in with a backfed main? And finally, the panel will be surface mounted. when I run the studs from joist to floor, I'll put cross boards between to attach the panel to. – Michael May 11 at 4:01
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    @Michael -- it protects the panel busbars from overcurrents (from any cause), as well as protecting the service lines from overload (but not short-circuits or gross ground-faults). Also, there is no hazard of having the main breaker present if a backfed main is also present (otherwise generator interlock kits wouldn't fly) – ThreePhaseEel May 11 at 4:07
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    So let me ask you, why does the wiring diagram state that you need to leave the opposite spaces open when using a backfed breaker? – Michael May 11 at 4:22
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    @Harper After installing a hold-down clip on that 100A breaker, it is not possible to use the spaces on the opposite side - so, I did end up losing 4 spaces. I can get by without them. When all is said and done, I believe 22 spaces will be used for 20 circuits. – Michael Jun 12 at 22:13

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