Red Seal Electrician Practice
Safety and work practicesQuestion 1124 of 1506

The secondary of a CT is left open (no ammeter and no shorting link) while the line carries current. What can happen?

  1. The CT output current drops to zero and the circuit is safe.
  2. The CT switches itself to a lower ratio to protect the winding.
  3. The CT can produce extremely high secondary voltage.
  4. The ammeter reading is kept by the core until it is reconnected.
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Correct answer: The CT can produce extremely high secondary voltage.

A CT is wound as a voltage step-up device. With no load path it makes very high voltage, which is dangerous to people and equipment.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 10.7: Special Transformers and Applications

Practice safety and work practices

Questions last reviewed: 18 October 2026