Safety and work practicesQuestion 1125 of 1506

A CT has a short-circuiting switch across its secondary. When must the switch be closed?

After the ammeter is put back
When the ammeter reads full scale
Before the ammeter is taken out for service
Only when the line is de-energized

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Correct answer: Before the ammeter is taken out for service

Shorting the secondary gives the CT current a safe path before the ammeter leaves the circuit. An open CT secondary can make a dangerous voltage.

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

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Questions last reviewed: 18 October 2026

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