Tom Bishop, PE
EASA Senior Technical Support Specialist
Often when we are dealing with three-phase squirrel cage motors we ask ourselves “Is there a standard or a rule of thumb for this motor characteristic?” The 10 characteristics that follow apply to conditions associated with motor starting as well as steady state operation. Examples are provided for each of the characteristics. Where applicable, the source NEMA or IEC standard clauses are cited in Table 1.
| Table 1: Motor Characteristics with NEMA and IEC References |
| Topic |
NEMA MG 00001 |
IEC 60034-1 |
| 1. Voltage variation |
12.44 & 20.14 |
7.3 |
| 2. Voltage unbalance |
12.45, 12.36.2 & 20.24 |
none |
| 3. Current variation |
12.47 |
none |
| 4. Current unbalance |
14.36.5 |
none |
| 5. Full load current |
12.47 |
none |
| 6. Locked rotor current |
10.37.2 |
* |
| 7. Instantaneous current at starting |
12.36 |
none |
| 8. Locked rotor stall time |
12.49 |
none |
| 9. Number of starts |
12.54 & 20.12 |
none |
| 10. Slip (synchronous rpm – rated rpm) |
12.46 |
12.1 |
| *IEC 60034-12 provides values for locked rotor apparent power. |
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