NEMA contactors for low-voltage motors (less than 1000 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 0, 1, 2, 3, 4,5,6,7,8,9,
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 1000 volts) are rated by voltage and current capacity.
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 (1.c. AC or DC) and the number designates the maximum voltage design values.
