Loadcenter rating; Bus vs. MCB

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Bill VB

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Master Electrician
Are some, most, or all manufacturer's rating their bus bars at a percentage rating higher than the rated MCB?? ex. 100A MCB rated with a 125A bus bar rating. Thx.
 
Most bus bars are sized for the maximum rating available in the panel. It costs too much to manufacture and inventory multiple parts.

However just because the bussing may be larger, it is the overall ' tested at' value that determines the complete panel rating. There is no real margin of error or slop built into a rating.
 
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Bill VB said:
Are some, most, or all manufacturer's rating their bus bars at a percentage rating higher than the rated MCB?? ex. 100A MCB rated with a 125A bus bar rating. Thx.
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I know that all the Eaton CH panels from 150A to 225A have 225A busbars; we have it in writing from Eaton. That often comes in handy for landing backfed PV breakers in CH panels.
 
Bill VB said:
Are some, most, or all manufacturer's rating their bus bars at a percentage rating higher than the rated MCB?? ex. 100A MCB rated with a 125A bus bar rating. Thx.
Click to expand...
It's not that they over size the bus per se, it's more of a quirky labeling thing. If you buy a panel with 125A bus and Main Lugs Only or maybe "Convertible Mains", the label will say it is rated for 125A. If you buy a kit to install a 125A Main Breaker or a 100A Main Breaker the PANEL is still rated 125A. But if you buy the SAME panel with a factory installed 100A main breaker, the panel nameplate might say it is rated for 100A. The bus bars inside are still going to be 125A rated, but the label on the panel with a factory installed main will be based on the main breaker rating. It's a quirk with how each individual manufacturer listed their panels with UL. Some figured it out, others didn't.
 
ggunn said:
I know that all the Eaton CH panels from 150A to 225A have 225A busbars; we have it in writing from Eaton. That often comes in handy for landing backfed PV breakers in CH panels.
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Exactly my use. TY
 
Jraef said:
It's not that they over size the bus per se, it's more of a quirky labeling thing. If you buy a panel with 125A bus and Main Lugs Only or maybe "Convertible Mains", the label will say it is rated for 125A. If you buy a kit to install a 125A Main Breaker or a 100A Main Breaker the PANEL is still rated 125A. But if you buy the SAME panel with a factory installed 100A main breaker, the panel nameplate might say it is rated for 100A. The bus bars inside are still going to be 125A rated, but the label on the panel with a factory installed main will be based on the main breaker rating. It's a quirk with how each individual manufacturer listed their panels with UL. Some figured it out, others didn't.
Click to expand...
Throwing it out there for calculations regarding back-fed CB's for PV power per 750.12(B)(2)(3)b. Thx.
 
jim dungar said:
Most bus bars are sized for the maximum rating available in the panel. It costs too much to manufacture and inventory multiple parts.

However just because the bussing may be larger, it is the overall ' tested at' value that determines the complete panel rating. There is no real margin of error or slop built into a rating.
Click to expand...
Probably should have used the term "listed at" rather than "rating". Thx.
 
jim dungar said:
Most bus bars are sized for the maximum rating available in the panel. It costs too much to manufacture and inventory multiple parts.

However just because the bussing may be larger, it is the overall ' tested at' value that determines the complete panel rating. There is no real margin of error or slop built into a rating.
Click to expand...
Throwing it out there for calculations regarding back-fed CB's for PV power per 750.12(B)(2)(3)b. Thx.
 
Jraef said:
But if you buy the SAME panel with a factory installed 100A main breaker, the panel nameplate might say it is rated for 100A. The bus bars inside are still going to be 125A rated, but the label on the panel with a factory installed main will be based on the main breaker rating. It's a quirk with how each individual manufacturer listed their panels with UL. Some figured it out, others didn't.
Click to expand...

This. Siemens seems to be one that figured it out. The label in the panel in my home is "Ratings: 200A MAXIMUM - SEE MAIN BREAKER RATING IF USED. BUS RATED 225A. BACKFED BREAKER REQUIRES HOLD-DOWN MEANS. 120/240V~ 60HZ 1Ø 3W 208Y/120v~ 60hZ 1Ø 3W'

-Jon
 
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