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 |
, whichever is less. |
| Example: | 25 hp, 4 pole, load Wk² = 50 From Table, A = 8.8, B = 122. |
||
|
Starts per hour = |
122 |
= 2.44 | |
Calculated value is less than A. Therefore allowable starts/hour = 2.44.
Note: Table is based on following conditions:
- Applied voltage and frequency in accordance with NEMA Standards MG 1-12.44.
- 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.
- 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.
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