Allowable Starts and Starting Intervals
Design A and B Motors

 HP 2 Pole 4 Pole 6 Pole A B C A B C A B C 1 1.5 2 3 15 12.9 11.5 9.9 1.2 1.8 2.4 3.5 75 76 77 80 30 25.7 23 19.8 5.8 8.6 11 17 38 38 39 40 34 29.1 26.1 22.4 15 23 30 44 33 34 35 36 5 7.5 10 15 8.1 7.0 6.2 5.4 5.7 8.3 11 16 83 88 92 100 16.3 13.9 12.5 10.7 27 39 51 75 42 44 46 50 18.4 15.8 14.2 12.1 71 104 137 200 37 39 41 44 20 25 30 40 4.8 4.4 4.1 3.7 21 26 31 40 110 115 120 130 9.6 8.8 8.2 7.4 99 122 144 189 55 58 60 65 10.9 10.0 9.3 8.4 262 324 384 503 48 51 53 57 50 60 75 100 3.4 3.2 2.9 2.6 49 58 71 92 145 170 180 220 6.8 6.3 5.8 5.2 232 275 338 441 72 85 90 110 7.7 7.2 6.6 5.9 620 735 904 1181 64 75 79 97 125 150 200 250 2.4 2.2 2.0 1.8 113 133 172 210 275 320 600 1000 4.8 4.5 4.0 3.7 542 640 831 1017 140 160 300 500 5.4 5.1 4.5 4.2 1452 1719 2238 2744 120 140 265 440

 Where: A = Maximum number of starts per hour. B = Maximum product of starts per hour times load Wk². C = Minimum rest or off time in seconds between starts.

Allowable starts per hour is the lesser of (1) A or (2) B divided by the load Wk², i.e.,

 Starts per hour < A or B          Load Wk² , whichever is less.
 Example: 25 hp, 4 pole, load Wk² = 50 From Table, A = 8.8, B = 122. Starts per hour = 122 50 = 2.44

Calculated value is less than A. Therefore allowable starts/hour = 2.44.

Note: Table is based on following conditions:

1. Applied voltage and frequency in accordance with NEMA Standards MG 1-12.44.
2. During the accelerating period, the connected load torque is equal to or less than  a torque which varies as the square of the speed and is equal to 100 percent of rated  torque at rated speed.
3. External load Wk² equal to or less than the values listed in Column B.

For other conditions, consult the manufacturer.
Reference: NEMA Standards MG 10, Table 2-3.