Machinery's Handbook, 31st Edition
ELECTRIC MOTOR STANDARDS 2645 Table 2. NEMA Standard Locked-Rotor Torque of Single-Speed Polyphase 60- and 50-Hertz Squirrel-Cage Integral-Horsepower Motors with Continuous Ratings
Designs A and B
Design C
Synchronous Speed, rpm
60 hertz 3600 50 hertz 3000
1800 1500
1200 1000
900 750
720
600
514
1800 1200 900
HP
… … … 1500 1000 750
Percent of Full-load Torque a
… … … 140
140 135 135 130 125 125 125 120 120 120 120 120 120 120 120 120 120 120 115 115 115
115 115 115 115 115 115 115 115 115 115 115 115 115 115 115 115 115 115 115 115
110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 …
… … … … … … … … … … … … … … …
1 ∕ 2 3 ∕ 4
… … 175
135 135 130 130 130 130 125 125 125 125 125 125 125 125 125 125 125 120 120 120
1
… 275
170 165 160 155 150 150 150 140 135 135 135 135 135 135 135 125 125 120 120
175 170 160 150 140 135 130 130 130 130 125 120 120 105 105 100 100 100
250 235 215 185 175 165 160 150 150 150 140 140 140 140 125 110 110 100
1 1 ∕ 2
2 3 5
… 250
225 225 200 200 200
250 250 250 225
250 225 225 200
7 1 ∕ 2
10 15 20 25 30 40 50 60
200 for all sizes above 15 hp.
75 100 125 150
For Design D motors, see footnote.
200 … … a These values represent the upper limit of application for these motors. Note: The locked-rotor torque of a motor is the minimum torque which it will develop at rest for all angular positions of the rotor, with rated voltage applied at rated frequency. The locked-rotor torque of Design D, 60- and 50-hertz 4-, 6-, and 8-pole single-speed, polyphase squirrel-cage motors rated 150 hp and smaller, with rated voltage and frequency applied is 275 per- cent of full-load torque, which represents the upper limit of application for these motors. For motors larger than 200 hp, see NEMA Standard MG 1-12.37. Table 3. NEMA Standard Breakdown Torque of Single-Speed Polyphase Squirrel- Cage, Integral-Horsepower Motors with Continuous Ratings
Synchronous Speed, rpm
60 hertz 50 hertz
3600 3000
1800 1500
1200 1000
900 750
720
600
514
… … …
Horsepower
Percent of Full Load Torque Designs A and B a
… … … 225
200 200 200 200 200 200 200 200 200 200 200
200 200 200 200 200 200 200 200 200 200
200 200 200 200 200 200 200 200 200 …
1 ∕ 2 3 ∕ 4
… … 275
220 215 210 210 205 205 200 200 200 200 200 200 190
1
… 300
265 250 240 230 215 205 200 200 200
250 240 230 215 200 200 200 200
280 270 250 225 215 200 200 200
1 1 ∕ 2
2 3 5
7 1 ∕ 2
10-125, incl.
150 200
… …
Design C
3 5
… … 225
… … … … … … … … …
… 200 … 190
200 190
7 1 ∕ 2 -200, incl.
a Design A values are in excess of those shown. These values represent the upper limit of the range of application for these motors. For above 200 hp, see NEMA Standard MG1-12.38.
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