Excess temperatures measured directly on the faulty part are usually divided into
three categories relating to 100% of the maximum load.
The start of the overheat condi-
tion. This must be carefully
monitored.
< 5°C (9°F)I
Developed overheating. It must
be repaired as soon as possible
(but think about the load situa-
tion before a decision is made).
5–30°C (9–54°F)II
Acute overheating. Must be re-
paired immediately (but think
about the load situation before
a decision is made).
>30°C (54°F)III
188 Publ. No. 1558792 Rev. a460 – ENGLISH (EN) – July 1, 2010
28 – Introduction to thermographic inspections of electrical installations