Moeller Electric’s PKZM0 fuseless motor protection circuit breakers combine the function of isolation, motor switching, short circuit and overload protection in a single unit, enabling highly efficient motor starters to be assembled from just a circuit breaker and a contactor.
The conventional fuse-based approach to protecting motor systems requires designers to spend a great deal of time selecting the correct components. Duty level, size of prospective fault currents and the type of short circuit protection needed must all be taken into account.
There is often a degree of uncertainty over prospective fault ratings, leading to problems in specifying the right components. Particular care must be taken to ensure that type 1 or type 2 coordination for the whole system is not invalidated.
A three-phase motor using the conventional approach would require no fewer than nine separate components to be specified: 3 fuse bases, 3 fuse links, 1 three phase isolator, 1 three phase contactor and 1 three phase thermal overload relay.
Moeller claims that the modular design of the PKZM0 allows designers to quickly and easily select and construct a complete coordinated starter combination.
When using the PKZM0/DILM combination, all the designer has to do is choose from a selection chart which matches the PKZM0 device chosen with the required DILM contactor.