Hot breaker

This is the hottest breaker I have come across yet. It is a 125 AMP breaker for a electric furnace.

129 F

Can anyone confirm that this temperature is acceptable for a square D breaker?


Is that just a single pole breaker for such a load? What was the ambient temp?

That is a 240 V

Ambient temperature is unknown, this temperature was taken while the appliance was running full out.

Your ambient temp is in the image you posted provided you correct for emissivity and reflection. Ambient temp should ALWAYS be known when performing thermal imaging in my opinion. Especially around electrical equipment. How can you accurately interpret the image without it???

I was taught UL standards 20 and 498 state a temperature difference between a component and ambient temperature of 30°C (54°F) may indicate a problematic component.

Other standards provide incremental temperatures and their corresponding degree of severity.

Do you have an image with the deadfront off so we can see the wires?

You may also want to manipulate the span and look to see if the breaker
is uniformly “hot” verses just a smaller area.

Like previously mentioned it is important to have the ambient temperature
to be able to determine if the 54f delta is met. Without the ambient it is just
a WAG.

Square D technical support said the overprotection device should be running at 40 C / 104 F

Here is the latest find.


To answer your first question, I need to know what amperage draw that was on the circuit at the time you took to scan.

I need to know the ambient temperature of the panel.

From what I’m looking at, I don’t see a problem concerning the temperature. But if you have a 125 amp breaker and your only drawing 40 amps, you got a problem.

Remember, if your comparing an indirect " un-corrected" thermal temperature reading of a circuit breaker, it is not the same as measuring a direct temperature reading with the ambient panel temperature.

The internal components could be 800 % higher than the indirect reading that you’re taking.

From your follow-up posts, I will assume that you did not take the appropriate readings to determine “corrected thermal temperature”. If you auto adjust your initial scan you can come close to your ambient temperature.

This is the problem that you encounter when you try to do quantitative thermal imaging when qualitative data is required to determine what a potential failure rate may be.

When we use “apparent temperatures” in quantitative analysis, we are reporting apparent issues. That is, unsubstantiated defects that may or may not actually exist.

Yes, I’m making rocket science out of button pushing thermal imaging training! However if you would like the answer, you must do what is required. (This is not directed at you Mark, rather the responses that will soon follow).

If you really want to know the answer to your question, you can e-mail me and I would be more than happy to provide you with a program to determine the load correction and how to use it.

Great information David and I highly appreciate it.

But to simplify, the discussion that I had with the Square D technical support stated the breaker should be running no higher than 40 C under a load. What is your take with this statement? Thank you.


I’m not David but I’ll just jump in.

40C is 104F. Todays temp here in AZ was 104F. We have most service panels on exterior of homes. Ambient temperature of the breaker without any load could exceed what you were told by the Sq D folks. Add any load at all to the picture and now what would the Sq D folks say. This is where ambient temp, load on breaker and all the other important stuff David has posted comes into play.

Also, if you could have images closer, and with dead front off it would help identify location of problem.(if one exists)

As Jeff pointed out, their 40C is based on a “design” ambient.

They did not give you all the information.

Also as Jeff pointed out, climb up on the breaker after you take a reference shot. Your SSR may average too much to get a good reading at that distance.

You need something like this to overcome the indirect aspect of the scan…

This is not a problem breaker by the way. :wink:

Pics with dead front off.

Many (most?) electrical devices are designed to operate satisfactorily at a stated temperature RISE of no more than 40 deg. C ambient. So what they are really saying is that if the device temperature is no more than the stated rise over 40 deg. C, the device will be able to dissipate heat generated internally adequately. All that said, in a panel full of similar beakers, any breaker that is substantially hotter than those surrounding it bears further investigation, especially if the maximum temperature is observed to be at the connection terminal itself. An elevated temperature may be due to many factors, including load approaching the breaker’s rating, but most such situations ae due to a deteriorating connection. Determination of the actual cause is outside the SOP.

So is the thermal imaging.
Should we do thermal imaging and then say that we do not have to determine the cause?

Technically you do not have to state the cause, just the abnormal observation. Think of it the same as an appliance that does not work properly - that’s all you know - not likely you know the cause.

But when you can tell what the cause is by just looking at the scan, why not report it?

The electrician (without TI) has little to go on to correct the situation.
Y not report, the source of heat “appears” to be from a loose connection at the wire connection etc?

That is your option; however, by stating that you know the cause you are taking on a bit more liability. In any event I agree we should use words like “appears to be…” or "may be… " or something similar.

Electricians would approach the resolution of the problem in various ways depending on how he is equipped. Assuming you include your IR image in your report, it would give him a good start

Leaving the house in the morning is a liability :wink:

My point is that you use a TI scan, then tell the client to get it looked at and expect someone to fix it… (nothing more)

Put on your electrician hat.
You have a hot breaker to evaluate.
Nothing is burnt, just warm.
1st you check how tight the wire is attached.
Then you pull the breaker. Nothing to see here.
Do you replace the breaker because you can’t find anything or do you tell the owner that there is nothing wrong and the HI is nuts.

The latter is generally what happens.

If you have been “trained” in TI, you can accurately (100%) tell if it is; a heavily loaded circuit, loose wire connection, loose buss connection, bad breaker. There is no added liability here except that your doing and reporting more than not talking about it in the first place (unless you screw up because you don’t know what your doing like reporting on some reflection or something).

Just my opinion.

I like to **not **lay the groundwork for an argument with the trades.
Knowing all good and well that the electrician will not likely show up with a TI, and I am doing a specialized inspection, I think it is my job to also tell the electrician what is wrong so he can fix it instead of making him look like a dumb *** when he can’t find the problem in the visible spectrum of light.

You can’t be playing the “Limited Home Inspection” game when you go past the limits.
If your going to use TI, take on the responsibility and liability with it.

If you wish to tell the electrician what you believe is the cause and are confortable in doing so, then go ahead and do it. However, electricians have been repairing panels for many years without the benefit of TI. Here’s what I think would happen …

  • you report that breaker #23 appears to be ‘hot’.
  • electrician opens panel, puts finger on breaker case.
  • if it feels hot, he will remove it and inspect the breaker clips and bus.
  • If both look ok, he will replace with a new breaker, wait several minutes to see how hot the breaker gets then tell the homeowner he has ‘fixed’ it.

Not necessarily the best way to proceed, but real-world.

I often see it go the other way…

“Your just a HI, what would you know”?

I get the calls from the client stating the electrician can’t find anything wrong and he says your nuts!

I had a client call three electricians to change out a breaker in the outdoor HVAC disconnect (only three breakers) that I found (before IR).

She then called me to ask who was going to pay the bills as no one found anything wrong.

I was in the neighborhood and swung by, pulled the breaker and handed it to her. It looked like a chunk of charcoal inside and the buss was pitted.

She asked why they couldn’t find it.

“There are some questions I just can’t answer”!

The heat receptors in your hand have greater sensitivity that most IR cameras in use out there. The problem is the hand is not always properly calibrated, or overridden by the brain.

Post IR; there is no more arguing with the electricians.

It is my “job” not just to take the pretty IR scan, but to read it and tell them what the problem is.
If someone can’t do that, it is my opinion they are just a home inspector with a piece of equipment they don’t know how to use.