1200A 80% rated circuit breaker need Arc Reduction?

[zemingduan]

Hi I was always thinking 1200A circuit breaker will need the arc energy reduction per NEC 240.87. But when I read the code today, I found the code language is "Where the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted is 1200 A or higher,..." I am wondering most typical 1200A circuit breaker used for residential meter bank (supply the apartment units) main is 80% rated and doesn't need to be 100% rated. Does these typical 1200A circuit breakers above even have/need continuous current trip setting? So do they still need Arc reduction?

 

[jim dungar]

Effectively all circuit breakers are 100% rated for periods up to 3 hours, just like conductors.

If the 1200A breaker was truly only 80%, wouldn't you only need to run 960A of conductors?

 

[zemingduan]

Effectively all circuit breakers are 100% rated for periods up to 3 hours, just like conductors.

If the 1200A breaker was truly only 80%, wouldn't you only need to run 960A of conductors?

What do you mean by "Effectively all circuit breakers are 100% rated for periods up to 3 hours, just like conductors."? Then what is an 80% rated breaker?

See this breaker catalog from Eaton. What does the 80% rated mean?


IMHO, the overcurrent rating of 1200A 80% rated breaker is 1200A and you can not run 960A of conductors per 240.4(C) .

 

[zemingduan]

I guess I am confused with the continuous current rating of a breaker. Is the continuous current rating of a 1200A 80% rated breaker 1200A or 960A? Need some one to clarify and give me some educations.

 

[jim dungar]

I guess I am confused with the continuous current rating of a breaker. Is the continuous current rating of a 1200A 80% rated breaker 1200A or 960A? Need some one to clarify and give me some educations.

Circuit breakers are tested, by UL, at 100% in open air. They are applied at 80% when that are installed into enclosures, unless those enclosures have additional ventilation.

Per the NEC, you determine your load then you select your conductors and finally choose a protective device. For the most part, loads are evaluated as being continuous (at full load for more than 3 hours) or non-continuous (at full load for less than 3 hours). Conductors are selected using 125% of continuous loads and 100% of non-continuous loads. Circuit breakers are selected based on the conductors chosen. Using 125% is the same as creating to 80%.

Be careful of applying NEC terms to equipment. The manufacturer, and some engineers might say the 1200A breaker can carry 1200A continually upto 3 hours, while it can momentarily carry higher amounts, such as 7200A for 20 secs or 12000A for 1 sec.
It is also possible the 1200A breaker is supplied with a rating plug that limits the maximum settable current to a smaller value.

 

[ron]

The answer to your original question, as Jim is indicating, the 1200A breaker (80% rated) still needs arc flash reduction.

 

[zemingduan]

Circuit breakers are tested, by UL, at 100% in open air. They are applied at 80% when that are installed into enclosures, unless those enclosures have additional ventilation.

Per the NEC, you determine your load then you select your conductors and finally choose a protective device. For the most part, loads are evaluated as being continuous (at full load for more than 3 hours) or non-continuous (at full load for less than 3 hours). Conductors are selected using 125% of continuous loads and 100% of non-continuous loads. Circuit breakers are selected based on the conductors chosen. Using 125% is the same as creating to 80%.

Be careful of applying NEC terms to equipment. The manufacturer, and some engineers might say the 1200A breaker can carry 1200A continually upto 3 hours, while it can momentarily carry higher amounts, such as 7200A for 20 secs or 12000A for 1 sec.
It is also possible the 1200A breaker is supplied with a rating plug that limits the maximum settable current to a smaller value.

Thank you very much Jim! I got educated.