Loose lug?

Noticed that the top of this panel was warm with a thermal camera. Opened the panel and found that the right side service entrance lug was warm.
Digital thermometer read 345 degrees F.

Do you have a better thermal image? Did you by chance take amp measurements?

Maybe, possibly, probably, but why theorize?

Report the facts that you know: That you observed excessive temperatures at the right side feeder / breaker. That you recorded a temperature of 345F using a point radiometer. That actual temperature at the point of the exception is likely to be significantly higher than what you recorded. That if the electrical load is increased, temperatures could rise dramatically higher than what you observed. This is an issue that needs to be addressed with some urgency.

The infrared image is unusable. I certainly wouldn’t include that in any report. Isn’t that a fire rescue imager?

BTW: Temps this high will change the properties of the metal conductors, insulation, etc… They should expect to be replacing affected parts, not just tightening a terminal.

I did not have your kind of temps but yesterday’s inspection turned up a 1976 FP panel with some problems

Chuck… You are correct. I heard back from the electrician that I called in to check the panel. He will be replacing it because of damage caused by overheating. The thermal camera is a fire service model and it does not record pictures. (hence the picture of the screen). These pictures are not from an inspection, but rather from an odor investigation at my other job. (fire service) I was looking for feedback as to the likely cause of the overheat. I am thinking loose lug and or unbalanced load on panel.

Then it makes makes perfect sense why you had that imager.

Loose lug is the most common cause, but you couldn’t really tell from the info at hand, though you could definitely tell that there was an issue. Generally for connection issues you will look for a temp pattern that is high at the point of contact and dissipates rapidly as you move further away on the conductor. Even then you can’t necessarily be sure that it’s due to a loose connection, as oxidation can cause it also.

I will usually use the descriptive phrase “The observed thermal pattern is consistent with a loose or high resistance connection.”

Good find by the way.


There is actually a way to capture images from some of the fire cams. Almost all of them produce a video radio signal. Often times these are used in a smokey situation and the user cannot sometimes see the screen. So it transmits a radio signal back to a central command (usually a trailer, fire truck or whatever). The manufacturer may have something that can grab that signal and maybe even capture images.

I am not as familiar with the Bullard one as I am with the MSA one. We are an MSA distributor on all safety products, but never move their cameras just due to the nature of their limitations for the applications that almost all of our customers use IR for.

The really odd thing about the MSA and IR, is they had a 320x240 camera with radio video out and .50mk thermal sensitivity, all for less than $10k over 4 years ago! If they only had image capture and reporting software, they would have been way ahead of any of the competition. Talk about a missed opportunity on their part.

Jason Kaylor
VP of Specialty Products
AC Tool Supply
Net Zero Tools

Dear Scott:

Nice find!

Without any additional confirmation testing, it is not possible to say with certainty that you have a loose lug. Although molded case devices are subject to exceptions caused by loose lugs, there are several other adjacent connections within each pole of the device, any of which can cause the excess heating that you show.

The maximum operating temperature for a molded case breaker operating at 100% load is 60°C (140°F). With a measured temperature of 345°F (174°C) the exception that you show would be considered a Priority 1 and immediate investigation and correction by a qualified electrician would be in order.

As Chuck correctly points out, long term heating of copper and aluminum will permanently change their physical properties. Copper begins to anneal at 95°C (203°F); aluminum begins to anneal at 85°C (185°F). Once these metals exceed these temperatures, replacement is usually required for an effective long-term repair.

Temperature limits for electrical and mechanical components along with ways for assessing repair priorities are covered in depth in the Standard for Infrared Inspection of Electrical Systems and Rotating Equipment. This Standard and others like it are available through the Infraspection Online Store.

Hope this helps.