High Temperture at service lug?

One of the aluminum service wires at a sub panel I inspected today had a tempeture of about 135 degrees (at the lug). I have always used 140 degrees as a threshold for breakers but I do not know if this tempeture is of concern at the service lug. I know the temperture of the wire is less than it is rated for, however does a temperture at this level indicate a possible loose connection at the lug?
Any thoughts.


Is this a two pole breaker?
Did you take an IR shot of the panel further out?
Are the two conductors that are shown above the breaker the same as the ones connected to the breaker(s)?
After seeing the higher temp, I would have put a fork meter around the conductor to check the amperage. If the higher temp is local to near the lug and not a large length of conductor, it could be a loose connection. It could also be a large amp draw if much of the conductor is shown at a higher temp.
If you look back at your reference material/books, what does your class training tell you.


Thanks. There is no breaker. It is a sub panel and the two wires shown are the service conductors. Yes the wires at the top of the photo are the same wires. I am pretty new to thermography. I have taken one NACHi course and am signed up for a cert class next month so until then my formal training is limited. The wire itself was cooler but as you see in the photo that wire is somewhat hot for some distance. The connection at the lug was a hot spot, however. I have a tendancy to think it is simply a large draw as I always put the electrical system under load for at least 30 minutes prior to inspecting. I just had not seen a lug this hot prior to today. I don’t think it is hot enough to cause me much concern but wanted to get other opinions.

Several things to help you in electrical evaluation. Focused images before saving, amp draw on suspected anomalies and “like” components, distance shot to evaluate pattern on wire, emissivity setting, T reflect. Also need info on wind, ambient temperature, how long has cover been off, these things are just some of what can influence the image and the conclusions reached.

If the cause is load related you will see a similar thermal pattern along the length of the conductor. If the temperature drops off significantly as you move away from the terminal, it is more likely a loose or high resistance connection. The actual temperature is likely higher than your image indicates as it is out of focus. You need the broader picture and load data to properly analyze. The temperature associated with a loose or high resistance connection will increase exponentially in relationship to increases in current, so load data is important in assessing the priority of the issue.

When you think you may have an exception, you want to capture images which show more of the area around the component as the pattern is important. If you are going to shoot panels, especially if you are advertising IR service and publishing findings, you should have additional tools (e.g., a clamp meter to take load readings) and training. It will be helpful for you to familiarize yourself with relevant standards such as the NETA Standard for Maintenance Testing Specifications for Electric Power Distribution Equipment and Systems and Infraspection Institute’s Standard for Infrared Inspection
of Electrical Systems & Rotating Equipment.

Manage your liability by making sure you are properly trained and equipped for the services that you advertise and perform and follow a defined protocol.

Thanks. I am currently not advertising any thermography service. I am as always in the process of continueing education. I am also pointing it at everything during my inspections to help learn on the job. Thanks for your insight.

NOT advertising that was. Right now just learning. Once I have a certifiecation I will offer it as an additional service.

The scan is not in focus so the temp measurements are less than your recorded.

It’s not how hot, but the temp difference.

What was the amp load on the circuit.
You can’t call anything without that…

I do not know the amp load but now I know I need to. I will also follow the recommendations on taking better photos. Thanks all good information. I will continue to work on my certifications and education. I appreciate the responses.

If you’re doing this to gain practical knowledge and not advertising thermography services or publishing findings, then the next time you find a suspected anomaly, feel free to call me and I’ll help you work through how to approach it.

Not uncommon. We will assume the insulation on that conductor is at the 75 Degree C/167 Degree F column and the lug is equally rated . You really need to know whats connected to that leg in the system and not simply go by a temperature reading without the other factors involved.

Like actual amperage load and potential amperage load…

There are computations to estimate the temperature rise between actual load and maximum load for equipment on the circuit.

You don’t, but you possibly could have 5 A on a 20 amp circuit here.
Never intentionally load a hot circuit to see what happens!