Temperature rise of overloaded circuit breakers

[sherif_helmy]

Hi everbody,
According to IEC 60947, the circuit breaker is tested using "Temperature rise test" which is done at normal operational current. This standard defines the accepted temperature rise for this test. My question: Is there any standard or code that defines the temperature rise limits for the circuit breaker in the case of overload? By overload I mean that the current is greater than In (Nominal current)

 

[zog]

That test is just ensuring the bus and other conductors, and all connections, have a low enough resistance so heat rise does not become an issue. I do not know of any OL temp rise limits, but I deal with ANSI stuff, not IEC (Not very often at least).

 

[sherif_helmy]

Could you please tell me what is the number of ANSI code

 

[zog]

What type of breaker are you refering to? And if you are in Cario IEC will apply, not ANSI.

 

[sherif_helmy]

I am talking about moulded case circuit breaker. For the sake of comparison, I wanna know what ANSI says.

 

[templdl]

I am talking about moulded case circuit breaker. For the sake of comparison, I wanna know what ANSI says.

UL489
I am not use is 3' or 5'? of rated wire is used on the line and load end of the molded case breaker when the tests is performed.
Foot note (1) referes to additional test require for 100% rated breakers.

 

[zog]

I am talking about moulded case circuit breaker. For the sake of comparison, I wanna know what ANSI says.

Yep, UL 489 for MCCB's, I thought you were refering to large breakers.

 

[templdl]

I am talking about moulded case circuit breaker. For the sake of comparison, I wanna know what ANSI says.

Now, if may "read between the lines" on your request are you refering to a bredaker's derating when operating in a higher ambient temperature 40deg c or it's additional capacity when operating at a cooler temperature?
For example a 50A breaker which is calibrated a 40degC when installed in a 25degC ambient the curve will move to the right and the breaker will actually be 55A. The curve will move to the left at 50degc 46A and 60degC 42a.
This is true with breakers that have the bimetalic themal elements. Breakers that have electronic trips don't derate as such but do have an internal temperature sensor which will trip the breaker that is in danger of overheating. (I know, stuff that your mother never taught you.)

 

[templdl]

Another excellent refernce is NEMA AB4 publication: Selecting and Maintaining Molded Case Circuit Breakers. I believe the lated revision is 2009 but I can't see any reason why you couldn't reference and older copy as breakers haven't magically changed that much.
It has a procedure for field testing breakers which doesn't check for calibration but it gives you a good idea as to whether the breaker is within acceptable parameters.