Sparktrician
Member
JHZR2 said:A breaker should be able to support 100% of its rated capacity continuously.
Shop tools are no continuous loads; there are NEC rules that indicate that continuous (on for 3 hours or more continuously) should be protected by a breaker that is only 80% loaded for heating reasons. But that's not relevant for intermittent use loads.
If a breaker opens at 90%, something is wrong. In fact, at 101%, or 125%, it should take a little bit to trip. This is by design to avoid nuisance trips due to inrush. Under high currents it should trip instantaneously.
Most of the breakers I have used are rated at 135% overload for a finite period specifically to accommodate inrush current while protecting the equipment to rated load past that finite window.