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Allowable Starts and Starting Intervals
Design A and B Motors

HP2 Pole4 Pole6 Pole
ABCABCABC
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.

 

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