Hot Electrical Service

Infrared image of a 200 amp electrical service I documented from today’s inspection. Thermal image is from a Flir EX320. House was built 2003. Ambient temp was between 75 and 80F.

I also shot video here:

Couple of questions for the thermography and electrical experts here:

  1. The system was not properly grounded. The grounding conductors were never connected to the grounding buss. Could this have any affect (I don’t see how, but I’m open to other viewpoints)?
  2. How hot do you consider to be too hot inside the panel? Do you go by absolute temp, delta vs other components, both?

What was your RAT and what was the load on the main?

Do you have a digital. I hate guessing.

The panel was inside of a closed residential garage, so you can assume that the RAT was very close to ambient. I was the next hottest thing in the garage and though I may get steamed from time to time, I’m not that hot.

The hotspot that you see in the image is a black screw which secures the buss inside the panel. It’s probably one of the least reflective / highest emissivity surfaces in the panel.

The surface of the disconnect was yielding an indirect apparent temperature of about 180F with the dead front inplace, which I could confirm tactilely. That’s what prompted me to bring the IR cam in to take look at the panel in the first place.

As far as actual load on the main: I dunno??? Only high amperage draw stuff running at the time was three A/C units with a combined minimum circuit ampacity of about 55.

This was a home inspection, not a deep dive diagnostic analysis. I’ll defer the diagnostic exercise to the electrician, along with attaching the grounding system conductors to the grounding buss.

You ask;

We need to know some more things to determine “how hot is too hot”.

Remember we are not always looking for hotter reflections. Cold reflections cause grief too.

See the very cool area right next to the screw?
Why is it not conducting? It’s more than 100 degrees less and it is next to the screw!?
Why, because it is likely a “cold” reflection on a high emissive material. This effects everything else in the box too. You have to obtain RAT regardless if it is hot or cold.

Than treat it like a home inspector and forget about how hot is too hot because there is insufficient information to determine this. Just call it HOT.:-k

Do you think the screw was loose?

I don’t think the ground issues would effect this.

Ok then I think you misunderstood what I was trying to get at with my second question.

I wasn’t looking for someone to tell me if THIS panel was too hot. I’ve already made that determination. What I am curious about is what method the rest of our thermographers and electrical gurus here use to determine if components in a panel are hot enough to be noteworthy and what kind of thresholds people use to decide whether to comment on an item.

I’ve heard several different methods/approaches expressed, but not a consensus. So what I’d like to hear from you David (and anyone else) is when you observe what you think is a thermal anomaly in an electrical component, what process do you go through to decide if it needs to be reported as an issue?


I’ve never had to call out an electrical panel due to overheating because all hot-spot temperatures were in the low hundreds.

In your situation, you have a temperature of 226 degrees Fahrenheit. I’d be calling this one out for an Electrician’s attention. I can’t see how this would be a temperature of no concern, at the SE connection point.


There are two methods of repair priorities:

  1. Delta-T (temperature differential)
  2. Absolute Temperature measurement (level II)

For the example given, let’s focus on Delta-T.

You can obtain a Delta-T by comparing similar component under similar load or by ambient air temperature. Since you are looking at a residential main disconnect, let’s assume that there is no other “similar” component. Therefore, you should be concerned with ambient air temperature.

Steps for calculating apparent Delta-T:

  1. Make sure your camera is set to E=1.0
  2. Measure the reference and the anomaly
  3. Calculate the apparent Delta-T (ar1-sp1= D1)
  4. Select priority guide (subjective)

The 4th step in this process is the answer to your question “How hot is too hot?”

You will have to make a decision on which standard to reference, but NETA is the most widely accepted and used. I would have called this out as an ADVERSE CONDITION, with a recommendation for IMMEDIATE ACTION by a QUALIFIED Electrician.

Suggestion: next time you document an anomaly, make sure that your area box (ar1) covers just the thermal anomaly. Then, take your spot (sp1) and place it outside the box in the coolest part of the image. This will be conservative, but it’s the better way to document the Delta-T.

May I also suggest getting a copy of the Infraspection Institute Standards.

Hope this helps :slight_smile:


Thanks Kevin.

Good info and very helpful.

So am I to “assume” that no one cares what the electrical load is on the circuit?

I guess we will “assume” that the “apparent” temp is correct?

Guess we will assume that you got it right…

**For this particular thermal anomaly, It does not really matter! The “exception” is 170+ Deg F over ambient. **

**It’s not always necessary to conduct “Absolute” temperature measurements in order to diagnose a thermal anomaly.

He got it right!!


Go ahead and assume whatever you like. You already seem to have assumed (incorrectly) that I needed you to audit my work.

I’ve already told you that the panel was in an enclosed residential garage and with an ambient temp of about 75F and that the only other warm object in there was me. RAT was not going to have a significant factor on the reading, and it certainly isn’t going to tell you anything about the specific object reflection on the shiny polished buss. The fact that the shiny buss is reflecting a cooler object is irrelevant as there are other much higher emissivity, less reflective surfaces to take readings from. You seem to forget that this was first and foremost a home inspection and there is already ample information to make the determination that review by an electrician was warranted. The simple fact that the surface of the main disconnect was too hot to put your fingers on, by itself is adequate to call for an electrician. I had made that determination before I even uncased the camera.

Now if you care to answer the question that I asked regarding the methodology YOU use, please go for it, I’m interested in hearing it. If you want to question what I’ve done in an attempt at self-aggrandizement, then get lost.

Measure the “hot” spot with a calibrated contact thermometer.


Made from what?

See here:

The part is energized.

I think I will pass on attaching a type K thermal couple to an energized circuit.

  1. The subject “hot spot” was not energized.
  2. Safe to do. to exposed breaker areas (just not the lug or contact screw).

Hope this helps;

Unless I have totally misunderstood, the hot spot in the photo is a conductive and energized part, not the breaker.

No. The hot spot was the screw that held down the breaker. Not energized.

Make sure you buy a good quality contact. Isolated.

Or, you could just use a good, non-electric (non-thermocouple) contact thermometer. That also works.

You make it too easy. Is that allowed? :mrgreen:

Actually the hot spot was the screw that secured the buss to the backplane.

It is energized.