FPE Circuit Breaker 40d C Connection

[Jsim4109]

We have an existing FPE 225A circuit breaker with a sticker that states the breaker is rated at 40d C CU-AL Conn. How do I calculate the ampacity of the load conductors at 40d C?

 

[jim dungar]

We have an existing FPE 225A circuit breaker with a sticker that states the breaker is rated at 40d C CU-AL Conn. How do I calculate the ampacity of the load conductors at 40d C?

That is the maximum ambient temperature for the breaker. You do not use this temperature in any conductor ampacity calculation.

You will see this max 40 degree rating on almost every molded case breaker, you can find.

 

[Jsim4109]

Thank you very much.

 

[infinity]

Greater than 100 amp it likely has 75° C terminals.

 

[Jsim4109]

I assumed that but the 40d C threw me off. I thought that referred to the temp of the terminals.

 

[infinity]

I assumed that but the 40d C threw me off. I thought that referred to the temp of the terminals.

There is really no reason to even include the 40 degree C marking on the CB. It just causes unnecessary confusion.

 

[Jsim4109]

Ok thanks. Thought i was nuts. I am, but for other reasons lol. Thank you.

 

[jim dungar]

There is really no reason to even include the 40 degree C marking on the CB. It just causes unnecessary confusion.

I think it may be a 'standards' requirement. I can't think of ever seeing a molded case breaker without it.

 

[infinity]

I think it may be a 'standards' requirement. I can't think of ever seeing a molded case breaker without it.

You're probably right, something that's been there for decades but most electricians have no idea what it means.

 

[Jsim4109]

Thank you. I don't remember ever seeing it but cant say i looked for it either. This one there us for a loop . thank you for the help.

 

[Jraef]

You will see this max 40 degree rating on almost every molded case breaker, you can find.

That's actually the basis for the UL489 listing of molded case circuit breakers. The only time it is different is if you NEED a higher temperature rating, for which you pay through the nose. I once had to buy some breakers rated for 60C operation (in a boiler room of a ship), they were 5x the cost of a standard breaker. Extreme cold requires special breakers too by the way.

 

[jim dungar]

That's actually the basis for the UL489 listing of molded case circuit breakers. The only time it is different is if you NEED a higher temperature rating, for which you pay through the nose. I once had to buy some breakers rated for 60C operation (in a boiler room of a ship), they were 5x the cost of a standard breaker. Extreme cold requires special breakers too by the way.

Yes, but I've always wondered why it needs to be shown on a standard breaker.

 

[JoeStillman]

Yes, but I've always wondered why it needs to be shown on a standard breaker.

The size and shape of the internal mechanism is different at different temperatures. Parts can go out of tolerance if it gets hot. If it isn't tested at higher temperatures, there's no guarantee it will work.

 

[kwired]

Yes, but I've always wondered why it needs to be shown on a standard breaker.

to confuse people

When Square D started putting big "10" and smaller "k AIC" on the exposed face of the QO breakers I've had many try to tell me the breaker in question (say on a phone call) is a 10 amp breaker. To some extent wish they never put this information on surfaces the typical user ever sees.

Also could be wrong but isn't the 40C the ambient temp that the device was calibrated to? Change the ambient temp and actual trip time will change for a given current level that is in the minor overload levels?