An induction motor draws current even when it turns without load. Most of this current is the magnetising current needed to build the magnetic field between stator and rotor; the rest covers iron, friction and fan losses. No-load current can therefore be a significant share of rated current rather than a small fraction, and the share is higher on small and multi-pole motors. Because this current is drawn largely as reactive current, the real power consumed at no load is low even if the current looks high.

A no-load current reading tells you about:

  • Phase balance: a clear difference between the three phases points to supply imbalance, a loose connection or a winding problem.
  • Correct connection: a wrong star/delta connection for the nameplate voltage raises no-load current abnormally.
  • Voltage: if the supply voltage is above the nameplate value, magnetising current and no-load current increase.
  • Mechanical condition: no-load current rising over time on the same motor may signal a binding bearing or friction.

Recording the no-load current at first commissioning creates a good reference for later comparison. For rated currents under load, see the electric motor current table.