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NEMA B Three Phase Squirrel Cage motors – Locked Rotor Current

The National Electrical Manufacturers Association has defined different torque profiles for three phase induction motors.  For example, design D offers high starting torque and might be advantageous in a drill or press application.

 

By far, the most common squirrel cage motor design is NEMA B which strikes a compromise between starting torque and slip speed (< 5% of at rated load).

 

For NEMA B motors, here is a listing of the maximum allowed locked-rotor current at 230V, as defined by MG 1 12.35.1.  For values outside 230V, NEMA states “The locked-rotor current of motors designed for voltages other than 230 volts shall be inversely proportional to the voltages”.  Which leads us to calculate the other values.

Locked rotor current (A)
Rated voltage
HP 200 230 460 575
0.5 23 20 10 8
0.75 29 25 13 10
1 35 30 15 12
1.5 46 40 20 16
2 58 50 25 20
3 74 64 32 26
5 106 92 46 37
7.5 146 127 64 51
10 186 162 81 65
15 267 232 116 93
20 334 290 145 116
25 420 365 183 146
30 500 435 218 174
40 667 580 290 232
50 834 725 363 290
60 1001 870 435 348
75 1248 1085 543 434
100 1668 1450 725 580
125 2087 1815 908 726
150 2496 2170 1085 868
200 3335 2900 1450 1160
250 4198 3650 1825 1460
300 5060 4400 2200 1760
350 5865 5100 2550 2040
400 6670 5800 2900 2320
450 7475 6500 3250 2600
500 8338 7250 3625 2900

 

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