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Circuit Breaker temperature ratings and the CEC #213889
08/23/14 08:00 PM
08/23/14 08:00 PM
Potseal  Offline OP
Joined: Feb 2013
Posts: 264
I was discussing code rules with another electrician and it involved an exam question from the ESAT Canadian Electrician Certificate of Qualification Practice Tool. The question was:

Q: What is the minimum size of AC90 cable that can be used to carry the maximum allowable electrical heating load that can be connected to a 240 V, 20 amp, 2-pole breaker?

A: Rules 62-114 and 4-006, Table 2, 75 degree column = #14 AWG

I have no problem understanding that breakers are rated at 60, 75, or 60/75 degrees (source: Schneider Electric) and therefore if the question only mentions "breaker" then you COULD assume 75 degrees for the termination temp. The problem is where in the code specifically does 75 degrees come from? If the termination temp of the equipment isn't specified (in this case, it's not specified in the question) then why would you assume the breaker's termination temp. is 75 degrees? It could be rated at 60 degrees. Poorly worded question or is the author of the question assuming you should know to use 75 degrees?

A malfunction at the junction
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Re: Circuit Breaker temperature ratings and the CEC [Re: Potseal] #213891
08/24/14 02:55 AM
08/24/14 02:55 AM
twh  Offline
Joined: Mar 2004
Posts: 928
Regina, Sask.
I would have guessed 12 AWG per 14-104(2). Because the ampacity in Table 2 is 20 amps subject to note referring to 14-104, which states that a conductor on a 20 amp breaker must be #12, I wouldn't think you could use that ampacity without applying the associated rule.

Perhaps we can look for an answer to the 75 degree assumption south of the border.

I don't think the question is worded so badly. I think the problem is that the Canadian Electrical Code is out of control.

Re: Circuit Breaker temperature ratings and the CEC [Re: Potseal] #213951
09/11/14 11:36 PM
09/11/14 11:36 PM
Potseal  Offline OP
Joined: Feb 2013
Posts: 264
Well, it bothered me enough to contact CSA. Here's the email reply:

All circuit breaker have been certified for use with 75 C conductor ampacity ratings. Circuit breakers are marked somewhere on the circuit breaker with a label that says, “60/75C wire”. Since all circuit breakers are marked the Rule doesn’t require the 75 C to be specified. This came about in the 2012 Canadian Electrical Code, when Rule 4-006 was changed. This now means that if a conductor terminates on a circuit breaker you must use the 75C column from Tables 1, 2, 3 or 4 to determine it maximum ampacity rating. We didn’t put the breaker temperature in the questions as the C of Q Exam doesn’t have to and also we didn’t want you to think that circuit breakers come with 90 C ratings.

4-006 Temperature limitations (see Appendix B)
(1) Where equipment is marked with a maximum conductor termination temperature, the maximum
allowable ampacity of the conductor shall be based on the corresponding temperature column from
Table 1, 2, 3, or 4.
(2) Where equipment is not marked with a maximum conductor termination temperature, 90 °C shall be used
by default.

Let me know if I can be of any further assistance.


Robert Nelson
Senior electrical Consultant – Learning Services
CSA Group

Last edited by Potseal; 09/11/14 11:37 PM.

A malfunction at the junction


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