Circuit breaker temperature ratings

[NEC User]

All wiring sizes are being calculated using NEC Table 310.15(B)(16). I'm using wiring rated for 90 degrees per the clients standard specifications. The client wants us to use the 75 degree column even though we're using 90 wire. This results in an increase in wire size. The client's reasoning is that other connector components within the circuit are only rated for 75 degrees.

My boss asked me to verify if NEC would require any alterations on the circuit breaker (such as temperature rating of the circuit breaker). I don't think so and i wasn't able to find anything in the NEC yet.

 

[petersonra]

Client is right. It appears there are few if any terminations rated above 75C for <600V.

You can start with the 90C column for derating purposes but the maximum ampacity of the wires is what is in the 75C chart.

 

[NEC User]

Can you confirm that cicuit breakers don't have temperature ratings.

 

[jim dungar]

Your client is correct to demand the use of the 75?C column.

There are no UL 489 listed breakers which are suitable for the termination of conductors sized using the 90?C column.

 

[NEC User]

So basically all circuit breakers used by contractors are rated for 75 degrees?

 

[templdl]

So basically all circuit breakers used by contractors are rated for 75 degrees?

The terminals. Older breakers may have 60degC terminals where the current breakers may have 60/75degC of 75degC terminals.
When a breaker is tested it is calibrated at 40degC. It is not that the breaker is rated 75degC, it is the terminals and the rating of the wire used with them.
When a test is Conducted the test on each pole of the circuit breaker is done by connecting the line and load terminals of that pole to
the test equipment by rated copper conductors not less than 4 ft (1.2 m) in length. When the terminals are marked 75degC that is the rated wire to be used. When the terminals are marked 60degC then 60deg rated wire must be used.
The wire acts as a heat sink for the breaker. If the wire is applied are 90degC for example then the wire adds to the heating of the breaker causing it to derate which essentially moves the trip curve to the left which results in the breaker being unable to carry its rating.
I am also not familiar with and motor control such as contactors and starters with terminal greater than 75degC either.

 

[NEC User]

Thank you for the clarification

 

[Ponchik]

Here is one bulletin from SQAUARE-D. Other manufacturers may have their own data. But mostly they are 75.

http://ecatalog.squared.com/pubs/Ci...eakers/QO-QOB Circuit Breakers/0600DB0103.pdf

 

[weressl]

So basically all circuit breakers used by contractors are rated for 75 degrees?

Circuit breakers are rated for operation at 40 Centigrade ambient temperature. There are some that is rated for 50 Centigrade. The terminals are designed to allow a maximum RISE of temperature 75 Centigrade over the ambient temperature at full rated current. Wires connected to the circuit brekers CAN utilize the lug ratings for determining their ampacity.

 

[templdl]

Circuit breakers are rated for operation at 40 Centigrade ambient temperature. There are some that is rated for 50 Centigrade. The terminals are designed to allow a maximum RISE of temperature 75 Centigrade over the ambient temperature at full rated current. Wires connected to the circuit brekers CAN utilize the lug ratings for determining their ampacity.

What is UL489?

 

[qcroanoke]

Client is right. It appears there are few if any terminations rated above 75C for <600V.

You can start with the 90C column for derating purposes but the maximum ampacity of the wires is what is in the 75C chart.

Agreed