Question regarding heat and breakers

[Marc M]

Jerry,
When attempting to determine the maximum temp of any given breaker while under load; can you please explain the most effective method used in determining this temp and what factors may or may not apply? For example, if one was to take the temp of a 40A breaker (for A/C) while in use, what is the temp of that breaker "not" to exceed and how do you determine this? Is it the listed temp or do other factors apply. I assume the conductor type used (depending on size) will also have to stay within the breaker temp ratings.
Thank you

[Jerry Peck - Codeman]

Hi Marc,

When attempting to determine the maximum temp of any given breaker while under load; can you please explain the most effective method used in determining this temp and what factors may or may not apply?

There is no answer to your question as stated, however, an answer can be given by establishing the conditions for the test and where the test for temperature should be taken, and that the temperature is not a given stated definite temperature, but a temperature rise from ambient, whatever ambient may be, in one test ambient temperature is given and the test is taken in open air, in another test the ambient is not given and the test is performed in the smallest enclosure in which the breaker under testing is approved to be installed in.

The temperature rise in UL 489 is:
- 50°C 'rise at the wire terminal connections' based on 100% rated current at 40°C in open air
- 60°C 'rise at the wire terminal connections' based on 100% rated current 'in the smallest enclosure' and with 90°C rated conductors used sized at 75°C from NEC 310-16 ampacity tables, in this example we will state the ambient in the smallest enclosure is 41°C or 105°F

Okay, how hot is that?
- 122°F rise 'at the wire terminal connections' based on 100% rated current at 104°F in open air, or, 226°F 'at the wire terminal connections'
- 140°F 'rise at the wire terminal connections' based on 100% rated current 'in the smallest enclosure' and with 90°C rated conductors used sized at 75°C from NEC 310-16 ampacity tables, in this example we will use the same ambient in the smallest enclosure of 41°C or 105°F, or, 245°F 'at the wire terminal connections'

To complicate matters, ANSI C37 allows for a 55°C rise at line and load terminal connections, 85°C temperature rise on circuit breaker contacts, with 100% rated current, and in then smallest enclosure.

From some other information I found, the handle on an AFCI breaker, and presumably all circuit breakers, must not exceed 60°C or 140°F.

[Marc M]

From some other information I found, the handle on an AFCI breaker, and presumably all circuit breakers, must not exceed 60°C or 140°F.

This I found and thought it to be the standard. However, it appears based on your answer that each and every situation is different and as such, much must be taken into consideration in order to determine the Max temp of that individual breaker/ circuit. I was using my friends IR gun and shot my panel. The A/C breaker was hotter than the rest so I wanted to find out what exactly is "too hot". I appreciate your help

[Jerry Peck - Codeman]

Hi Marc,

Not sure if I explained what I was saying well ...

From some other information I found, the handle on an AFCI breaker, and presumably all circuit breakers, must not exceed 60°C or 140°F.

This I found and thought it to be the standard. However, it appears based on your answer that each and every situation is different and as such, much must be taken into consideration in order to determine the Max temp of that individual breaker/ circuit.

There are multiple things being stated here (and on the first post, and which I tried to specify in my response):

One: The temperature of "the breaker".
Two: The temperature of "the terminal connections" in the breaker.
Three: The temperature of "the handle" of the breaker.

To address them in order:
- One above: "the breaker" - That is what you asked about in your first post and re-stated in your second post ... the temperature of "the breaker".
- Two above: That is why I specified ... " 'at the wire terminal connections' " in my first response. I wanted to differentiate between " 'at the wire terminal connections' " and "the handle" and "the breaker" ("the breaker" is what you had asked about).
- Three above: That is why I specified "the handle on an AFCI breaker, and presumably all circuit breakers", to differentiate "the handle" from "the breakers" ("the breakers" is what you had asked about).

The A/C breaker was hotter than the rest so I wanted to find out what exactly is "too hot".

What I am saying is that checking the temperature of a breaker tells you little about it. Yes, the a/c breaker would be hotter than other breakers, it has more current going through it.

However, to make those measurements meaningful, the temperature would need to be taken 'at the wire terminal connections' of the breaker, and, if you can get to it, the bus bar connection, AND, you would need to know the ambient temperature withing the panel with the cover on, AND, to make the number really meaningful, have the current through the breaker at 100% of the rating of the breaker, AND, ... and even then the numbers are not compatible to what was tested for the listing. Those tests were made under conditions which were different, 100% rated load at 40°C in open air (which you are not doing) and/or 100% rated load in the smallest enclosure the breaker is approved for use in (which you are not doing either).

Thus, taking the temperature of a breaker in a panel is ... fun to do and interesting ... but yields limited usable results. That is what I was saying.

Can you have a really hot breaker in a panel? Yep. Does it mean the breaker is bad? Nope. Could the breaker be bad? Yep. Could the breaker be good? Yep.

Is it more likely that the breaker/bus bar contacts are the cause? Very well could be. The main things, though, when checking breaker temperatures is: a) not to put a lot of faith in them; b) take the temperature at the wire terminal; c) not to put a lot of faith in them; d) take the temperature at the bus bar connection; e) not to put a lot of faith in them.

Should you recommend the breakers be checked out by an electrician? Certainly would be logical to do so, as long as you did not say they were "bad" or "too hot", only that they were "hotter than you expected".

[Marc M]

Thanks for you time and expertise, glad to to be here. I was paying for this info thru another site. $15 per question.

[Jerry Peck - Codeman]

Hi Marc,

Thanks for you time and expertise, glad to to be here. I was paying for this info thru another site. $15 per question.

Hopefully you are getting more than you are paying for here.

[Marc M]

Hi Marc,

Thanks for you time and expertise, glad to to be here. I was paying for this info thru another site. $15 per question.

Hopefully you are getting more than you are paying for here.

Roger that!

[Jerry Peck - Codeman]

Glad my information is worth more than "nothing".

[pbennett1]

From some other information I found, the handle on an AFCI breaker, and presumably all circuit breakers, must not exceed 60°C or 140°F.

This I found and thought it to be the standard. However, it appears based on your answer that each and every situation is different and as such, much must be taken into consideration in order to determine the Max temp of that individual breaker/ circuit. I was using my friends IR gun and shot my panel. The A/C breaker was hotter than the rest so I wanted to find out what exactly is "too hot". I appreciate your help

Can you post an IR photo of the target?

[Jerry Peck - Codeman]

Hi Peter,

I suspect that Marc did not take a photo of it, however, if he did, it would be nice to see the photo and what is shown in the photo, temperatures and locations.