Ambient temperature effect on Circuit Breaker Selection.

The main functions of electrical switchgear systems are to protect circuit from over load or short circuits, Isolate or separate a circuit for safe operation and maintenance.

The ambient temperature for domestic low voltage (<=630 V) Circuit breaker(CB) is 30 deg. And for industry is 40 deg. This ambient temp has a great effect on CB current rating. Because Bimetal Joint (thermal protection system) affects by ambient temp. Here given a table to show the affects of ambient temp on CB rating.

Rating(A)	20 Deg.	30 Deg.	40 Deg.	50 Deg.	60 Deg.	70 Deg.
100 A	110 A	105 A	100 A	95 A	90 A	85 A

 So the thermal protection system of a circuit breaker affected by ambient temperature and must in mind during selection a CB.