How hot is too hot for a breaker?

20 amp breaker/wire connection point. What is the normal temperature range (using an IR camera) and when should I be concerned. I saw one recently over 350 degrees. I know that’s too how. But what about 150? At what point would you refer it to a sparky?

How does it compare to similar breakers under similar loads and where was the hot spot located? Any photos?

Will have to post photos later. I didn’t measure the exact temp at others. But the one that I’m curious about was 150 and stood out as about twice as high as the others. Not sure what circuit it was.

It was an FPE and for that alone I called it out. Just curious about what to look for.

you should have picked this up by now, but you must know the amperage load and the potential amperage load on the circuit to determine how hot is too hot.

You should also have received in your training the method of determining how hot is too hot and the difference between direct and indirect measurements. Except for the terminal screw, everything about a circuit breaker is indirect measurement.

I don’t use IR just a infrared thermometer to check breakers.
I check the average temp. of the breakers and will note if one
is well above the average.

Good info here…

Great PDF’s. Thanks for sharing.

I know my Stab lok breakers are rated upto 40 celcius. Anything above is of concern.

I thought that UL had a requirement of 40° or 50°C above ambient temp for a maximum allowable breaker temp. I can’t find anything referencing it, but to what Ray mentioned, 40°C is only 104°F which is hardly a dangerous temp. That seems really low. You couldn’t even install that breaker in Arizona. :slight_smile:

Correct me if I’m wrong, but the 40C rating on a breaker is for ambient temp.

I believe that it is above ambient,.

Hello All,

I guess I will comment on this one for process purposes and leave it at that. As you know a Circuit Breaker that you all will come in contact with are also called inverse time circuit breakers, molded case circuit breakers and so on. These typical devices offer an two different operations points from instantaneous point to a overload point within the internal operation of the device. The instantaneous point is for ground fault and short-circuit and the overload portion of the curve is just for that overload.

The operation of the thermal portion of this device will be affected adversely by ambient temperatures and where the device is installed. For example, exterior panel enclosure with circuit breakers in an elevated ambient location (Arizona, facing the southern sun) the thermal latching points will be lower than installed in an area with a lower ambient temperature. If the established parameters of the thermal component of the device is affected the device will deactivate appropriately. However, as home inspectors what should I be doing in terms of thermal scanning of the devices.

  1. I wont talk about the high tech cameras in my method because I believe that can in general senses go above the basic standard of inspection. You should use a standard thermal gun and scan all devices within the enclosure.

  2. If any circuit breaker is running abnormally hotter than any other circuit breaker in the set then note it down on your report. What is abnormal ( again my opinion only) if you have a 40-60 degree difference (not including AFCI or GFCI Devices) you need to take a reading from the terminal point…not just the plastic circuit breaker so this would mean the cover had to be removed.

Keep in mind that the circuit conductor acts like a heat sync for the circuit breaker to help pull heat away from the terminal as well so keep that in mind.

Any time you find a circuit breaker operating well above the circuit breakers that are located adjacent to the one in question…always check what load is labeled on the panel that is to be associated with that circuit…just remember to take a reading from the device as well as the terminal point.

Lastly if you see a circuit breaker running at, I believe you said 350 degrees…remember that you are not an electrician so it is perfectly fine to defer this for more review by a licensed professional who will conduct a more deeper investigation. Do not look for a standard value…let what you find be your guide and defer when in doubt.


How would one deal with the low E/high reflective terminal post when taking a reading? Would the case directly adjacent to the post be an acceptable source for a proper temp, or with the dissipation even that close to the terminal make that an untrustworthy reading?


I can only give you my opinion based on the question asked regarding terminals within an electrical panelboard enclosure and circuit breakers. If you are speaking about terminations in general understand that temperature is very different on terminals not affecting an OCPD versus simply a terminal. For example a terminal lug by itself (no OCPD) can and in most cases operate at 100% of its listed rating…

Metal is a great dissipater of heat…but it is also a great conductor of heat as well so getting readings on metal surfaces beside a terminal and then on the terminal may not prove to be a good reading source. The good news here is the manufacturer of that terminal will have temperature guidelines for the terminal and indeed ambient can always play a role in adding to the heat.

So my advice on that situation would be to find out what the rating is of the terminal, what are its temperature limitations under evaluation if their is a concern and since this would more than not be a commercial environment I would not be afraid to ask for that if something appeared to be abnormal.

Also keep in mind that if we are talking about a terminal and a conductor of the wire type is terminating to it…we have to also protect the limitations of the conductor (wire) as well…its insulation and so on so you would still take a reading from the conductor (wire) and terminal and then be aware of the operating temperature values of the conductor in use…if it is an insulated conductor of course.

Just my thoughts on that…again you guys have ALOT to think about when doing an inspection…its a tough job and we do appreciate what you do out there and the concerns that are raised.