Red Seal Electrician Practice
TransformersQuestion 1139 of 1506

When is the inrush current of a transformer most severe?

  1. When the supply is connected at the instant the voltage is zero
  2. When the supply is connected at the peak of the voltage wave
  3. When the secondary load is open at the time of switching
  4. When the supply frequency is higher than the rated value
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Correct answer: When the supply is connected at the instant the voltage is zero

Starting at zero volts makes the flux go to about twice its normal peak and drives the core into saturation.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 10.8: Practical Considerations - Transformers

Practice transformers

Questions last reviewed: 18 October 2026