Frequently asked questions
How should thermal scans of circuit breakers be used?
28 September 2021
All MCCB and Masterpact circuit breakers
IR scans often contain images and verbiage indicating problems with the installation when no problem exists.
Thermal scans are best used as a preventative maintenance tool. The breakers should be benchmarked (preferably early in their service life), and subsequent tests at periodic intervals (typically annually) should be compared with the benchmark to see if anything has changed significantly. If so, investigate the cause. If these readings are within limits, and the breaker shows no evidence of overheating (discoloration, nuisance tripping, smell, etc.), record the reading and monitor to see if it changes over time.
For isolated scans (snapshots), a common practice is to compare the temperature of a breaker with the temperatures of similar breakers with similar loading. All temperatures should also be below the UL limits:
UL Surface Temperature Rise Limits
Non-metallic: 60 deg. C
Metallic: 35 deg. C
UL Terminal Temperature Rise
80% Rated CB: 50 deg. C
100% Rated CB: 60 deg. C
SEE ATTACHED for more information
If any breakers with similar loading are significantly warmer than others, the cause should be investigated. It is possible to have loose or high-resistance connections on either the line or load side. Check the wire torque--and check for discoloration and odors which would be a sign of excessive heat.
The way thermal scans are presented often needlessly alarms the customer. Colors on the scans are relative, so look at the numbers. Also, have an experienced third-party review the scan if there are recommendations for replacing breakers that have moderate temperatures and no signs of overheating other than the colors on a thermal scan.