<Li> DC - 13 - Control of electromagnets </Li> <P> NEMA contactors for low - voltage motors (less than 1,000 volts) are rated according to NEMA size, which gives a maximum continuous current rating and a rating by horsepower for attached induction motors . NEMA standard contactor sizes are designated 00, 0, 1, 2, 3 to 9 . </P> <P> The horsepower ratings are based on voltage and on typical induction motor characteristics and duty cycle as stated in NEMA standard ICS2 . Exceptional duty cycles or specialized motor types may require a different NEMA starter size than the nominal rating . Manufacturer's literature is used to guide selection for non-motor loads, for example, incandescent lighting or power factor correction capacitors . Contactors for medium - voltage motors (greater than 1,000 volts) are rated by voltage and current capacity . </P> <P> Auxiliary contacts of contactors are used in control circuits and are rated with NEMA contact ratings for the pilot circuit duty required . Normally these contacts are not used in motor circuits . The nomenclature is a letter followed by a three - digit number, the letter designates the current rating of the contacts and the current type (i.e., AC or DC) and the number designates the maximum voltage design values . </P>

Who invented the electromagnetic brake and automatic circuit breaker