Return to Table of Contents - EASA Engineering Handbook

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.

 

back to table of contents