Panel Size Reference

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To add some further confusion, the bus rating (is that what they mean by "mains rating"?) Is actually not 125. Even Siemens' smallest PB, a P1 has either 250 or 400A bussing. I don't know what the options are for a P2 off the top of my head. Frequently manufacturers will put the requested amperage in the label even if it's not a standard size.
 
The "mains rating" is intended to convey the manufacturer's declaration of what the bus bars can handle. Perhaps, as electrofelon said, the bus bars could really handle more, but that is all we are being told for this particular item.

I would therefore call this a 125 amp panel. I would infer that the MCB could theoretically be replaced by a 125 amp breaker, so that more load could be added to the panel. Here again, it depends on the manufacturer. Perhaps the space allocated for the main breaker cannot fit a 125 Amp breaker.
 
charlie b said:
The "mains rating" is intended to convey the manufacturer's declaration of what the bus bars can handle. Perhaps, as electrofelon said, the bus bars could really handle more, but that is all we are being told for this particular item.
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Sounds to me like it's not supposed to be the rating of the whole bus, but only the tabs where the main plugs in.

I think this partly because MCB is indicated as the mains (as opposed to a lug kit)

There's been discussion here before about the ratings of the tabs, whether it's 100a or 125a - depends on manufacturer, I'm sure
 
James L said:
Sounds to me like it's not supposed to be the rating of the whole bus, but only the tabs where the main plugs in.

I think this partly because MCB is indicated as the mains (as opposed to a lug kit)

There's been discussion here before about the ratings of the tabs, whether it's 100a or 125a - depends on manufacturer, I'm sure
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So where is says "Mains" is should not lists MCB size? Infinity did say the nomenclature was terrible maybe this is what he's referring to.
 
James L said:
Sounds to me like it's not supposed to be the rating of the whole bus, but only the tabs where the main plugs in.

I think this partly because MCB is indicated as the mains (as opposed to a lug kit)

There's been discussion here before about the ratings of the tabs, whether it's 100a or 125a - depends on manufacturer, I'm sure
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Remember this is a true commercial panel board that takes bolt on breakers. The MB connects to the vertical bus with a bus bar kit for the frame of the breaker. I haven't seen such a small MB in a Siemens panelboard before .
 
Alwayslearningelec said:
So where is says "Mains" is should not lists MCB size? Infinity did say the nomenclature was terrible maybe this is what he's referring to.
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My thought was a convertible, where a 125a lug kit could be used (hence, mains raiting) or a breaker up to that same rating ( yet choosing 100a mcb).

That was the only way I could reconcile the two numbers and the two phrases

But I was probably wrong on all accounts
 
Little Bill said:
My experience has been if the panel contains a main breaker installed by the mfg, then that is the rating of the panel.
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That is typical with load centers. With actual panelboards, you are more likely to have the manufacturer state the bus rating and not keep it top secret. But like I said, I have seen with Siemens panelboards before where in the label, they put the amperage of the bus that was requested/ordered not what it actually is.
 
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