80% rated CB at reduced current instead of 100% rated CB

[elec_eng]

I have a 800A CB Plug In unit from 4,000A busway for 800A continuous load. 800A CB specified was 100% rated CB so the feeder is sized for (3) sets of 300KCM.

The equipment vendor is proposing we use 1,000A CB with 80% rated, instead. Sounded like they have several 1,000A CB with 80% rated. They are proposing to set the trip at 800A so we don't have to change the feeder size. They said they tested this CB with 800A and didn't exceed the thermal rating.

Cost and physical dimension aside, I have two questions:

1. Code standpoint - Is this code compliant, specifically 215.2 and 215.3.
2. Not clear how 100% rated CB is tested but if 1,000A CB was tested with 800A load and pass the thermal testing, does it make this CB 100% rated at 800A?

 

[jim dungar]

Not clear how 100% rated CB is tested but if 1,000A CB was tested with 800A load and pass the thermal testing, does it make this CB 100% rated at 800A?

All breakers are tested at 100% in open air.
The problem is breaker and conductors need to be installed inside of enclosures, which means they could overheat if loaded to the maximum. So normal breakers and conductors used at 100% loading need to be oversized to allow for the poor heat disapation, the NEC requires a 125% multiplier.
However if enough ventilation is provided, byte manufacturer, a breaker can be listed for 100% loading.

Dialing the trip unit rating from 1000A down to 800A does not change it from a being an 80% to a 100% device,

 

[infinity]

The equipment vendor is proposing we use 1,000A CB with 80% rated, instead. Sounded like they have several 1,000A CB with 80% rated. They are proposing to set the trip at 800A so we don't have to change the feeder size

How does using a 800 non-continuous trip work with an 800 amp continuous load?