100 % Rated Device

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BCE

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is there any code section in NEC that states they will allow us to exceed
the 80% rating of a main service breaker, if the breaker is 100% rated
device? IE if there is a 200A service and your demand load exceeds 160 amps
at 277/480v-3ph-4w, can we spec the breaker to be at 100% rating and keep
the feeder at 200 amps?
 

Smart $

Esteemed Member
Location
Ohio
is there any code section in NEC that states they will allow us to exceed
the 80% rating of a main service breaker, if the breaker is 100% rated
device? IE if there is a 200A service and your demand load exceeds 160 amps
at 277/480v-3ph-4w, can we spec the breaker to be at 100% rating and keep
the feeder at 200 amps?
A typical Article 220 "demand" load calculation already compensates at 125% for continuous and 100% for non-continuous loads (when done accurately :D)... so you can have a "demand" calculated load of 200A on a 200A service.
 

Smart $

Esteemed Member
Location
Ohio
IE if there is a 200A service and your demand load exceeds 160 amps at 277/480v-3ph-4w, can we spec the breaker to be at 100% rating and keep the feeder at 200 amps?
FWIW, if your calculated load at 125% continuous load exceeds 200A, but does not at 100%, then yes you could change out or spec the ocp assembly at 100% and keep the same size feeder. However, I say "assembly" because it is the term used by the exception under which this scenario would be compliant. So I take that to mean not only the breaker has to be reated for 100% continuous duty, so does its enclosure and any other equipment and devices contained therein.
 

jim dungar

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Wisconsin
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Retired Electrical Engineer - Power Systems
FWIW, you will not find any 100% rated breaker smaller than an 800A frame size with electronic trip.
 

jim dungar

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Location
Wisconsin
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Retired Electrical Engineer - Power Systems
Siemens VL Series breakers are available in 100% rated versions down to a 150AF, which can have a trip unit as low as 30A.
Is it available in a panelboard mounted version? Most 100% rated devices I have seen require substantially more ventilation than 80% rated units.

And according to Square D their LE breaker is a 100% 400A frame available in I-line panel construction but not as a main in any other panel.
 

Jraef

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Electrical Engineer
Is it available in a panelboard mounted version? Most 100% rated devices I have seen require substantially more ventilation than 80% rated units.

And according to Square D their LE breaker is a 100% 400A frame available in I-line panel construction but not as a main in any other panel.

I think they just recently released the bus straps so that panelboard mfrs can use them (I used to work there, but don't anymore). But they themselves have not integrated these into their own panelboards yet. The VL Series breakers are, to the panelboard world, relatively "new", meaning they have only been available for a couple of years. It takes a long time to get all the UL listings done for panelboards in every possible configuration with every combination of devices. They are saying at least 2 more years...

What they do for now is publish specific minimum enclosure volume and ventilation requirements for 100% rated breakers.
 
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jim dungar

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Wisconsin
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Retired Electrical Engineer - Power Systems
I guess the real point is: a traditional 200A panelboard or loadcenter is not currently offered with an integral 100% rated main breaker.
 

Smart $

Esteemed Member
Location
Ohio
I guess the real point is: a traditional 200A panelboard or loadcenter is not currently offered with an integral 100% rated main breaker.

Because the exceptions which permit 100% rated ocpds uses the term assembly, wouldn't the entire panelboard need to be rated and listed for 100% operation?

An option would be a separately-enclosed main breaker feeding an MLO panelboard...
 
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