Table II-4. Voltage ratings for AC motors

DOE-HDBK-6004-99

Table II-4. Voltage ratings for AC motors

All motors for motor-operated valves and

480 volts, three-phase, 60 Hz

Class 1E damper motors

Motors 1/3 hp and below, except as

115 volts, single-phase, 60 Hz

specified in item 1 (above)

Motors from 1/2 hp through 250 hp

480 volts, three-phase, 60 Hz

Motors from 251 hp through 2500 hp

4,160 volts, three-phase, 60 Hz

Motors 3000 hp and above

13,800 volts, three phase, 60 Hz

All AC motors should be suitable for across-the-line starting. Non-safety-class motors should be

designed to accelerate the connected load with a minimum of 80% rated voltage at the motor

terminals. Safety-class motors should be designed to accelerate the connected load with a minimum

of 75% rated voltage. Wherever possible, DC motor starting current should be limited to 200% of

rated current. The full-voltage starting current of AC induction motors rated 250 hp or more should

not exceed 6.5 times the full-load current.

In general, motors 60 hp through 250 hp will be fed from load centers. Motors 50 hp and below, and

MOVs, will be fed from MCCs.

All safety-class motors should have non-hygroscopic Class F or Class H insulation with Class B

temperature rise. All non-safety-class motors should have at least Class B insulation sealed against

moisture and contaminants.

Enclosed motor windings should have moisture resistant Class B insulation systems, suitable for

power plant service, conforming to the requirements of NEMA Standard MG-1.

Class F or H insulation may be used if the temperature rise does not exceed limits for Class B

insulation.

All motors 3 hp and above located outdoors, and motors 25 hp or larger located indoors, should have

space heaters. Open, drip-proof motors 3 hp and larger in damp, indoor locations should have space

heaters. Wherever possible, space heaters should be rated for 220-240 volts, but are to be connected

to a 120 volt single-phase service.

All motors installed indoors should be open, drip-proof, and fully guarded or should be totally

enclosed, and fan cooled. Motors installed outdoors should be NEMA weather protected Type I or

should be totally enclosed and fan cooled.

Stator resistance temperature detectors (RTDs) should be provided for all medium voltage motors.

Rotor temperature monitoring should be provided on all motors above 1000 hp.