I have a 415 MCB of rating 200 Amps. is this current rating for both three phases or is per phase.
This MCB normally trips when the load is more than 150 Amps per phase. This has cause me to change it to new one thinking it is faulty. If the load is per phase why does it trip since the did not exceed 200 Amps per phase
200amps per phase, balanced load, if you have a short between phases this will be many thousands of amps for a split second causing it to trip (obviously ). if this is protecting a motor circuit it could indicate that the insulation of one of the motors windings is breaking down and failing above 150 amps, an insulation test would confirm this. also if your mcb is located in a very hot environment, this could cause it to trip early.
If this is a molded case breaker it is probably rated at 80%, which means that the thermal setting pick up would be at around 160Amps. Current more than 150A could activate this thermal pickup and this will trip the breaker in some period of time that is defined by that breaker Time Current Curve. You need to provide more information on your beaker and your scenario but my recommendation, assuming there is no abnormal conditions on your system (faults), is to install a larger ampacity circuit breaker. BTW: the current rating is the same for each phase, so if at any phase you have more that 160A on a 200A 80% CB, it will trip.
