The NEC or CEC requires that motor branch circuits be protected against overloads and short circuits. Overload protection may be provided by fuses, overload relays or motor thermal protectors. Short circuit protection may be provided by fuses or circuit breakers.    …more

The guidelines for applying R-Rated fuses are significantlydifferent from those applying to low voltage motor fuses.  This is because R-Rated fuses are back-up fuses which are intended to provide short circuit protection only for medium voltage starters and motors. …more