USCG Exam PracticeElectrical measuring devices and instrumentation
A current transformer (CT) secondary circuit is open while the primary conductor is carrying full load current. What is the immediate hazard?
- A. The CT core saturates and the primary circuit breaker trips on overcurrent
- ✓ Lethal high voltage develops across the open CT secondary terminalsCorrect
- C. The CT primary winding overheats because load current is redirected through the secondary
- D. The switchboard ammeter reads zero, causing the operator to incorrectly assume no load is present
Why B is correct
With the CT secondary open and primary current flowing, the transformer action drives all the magnetomotive force into producing a very high voltage across the open secondary terminals. This voltage can be lethal and can also destroy the CT insulation. The secondary circuit must never be opened while primary current flows.