I am looking into a series of 2 pole circuit breakers (Sprecher + schuh 's series KTU7 UL489 molded case circuit breakers) and they seems to have 2 ratings, a thermal trip rating and a magnetic trip rating. What is the difference between these two ratings? Is the magnetic trip rating the same as the instantaneous trip rating?
Fixed thermal Trip vs fixed magnetic trip current ratings
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The thermal setting is a thermal overload protection. It has a time-delayed response. The heavier the overload, the faster it trips. It may be implemented by something like a bimetallic strip.
The magnetic setting is instantaneous short-circuit protection. It has no intentional delay. It may be implemented by something like a solenoid plunger, restrained by a spring.
Here is an illustration of a typical time-current curve for a miniature circuit breaker (Clipsal 4 series) showing the thermal and magnetic trip characteristics. Note the thermal trip takes a long time - minutes or seconds - while the magnetic trip responds in 10ms or less.