USCG Exam PracticeElectrical measuring devices and instrumentation
A technician needs to measure the load current on a 440 V feeder without interrupting service. Which instrument and connection method is correct?
- A. A voltmeter connected in series with the feeder conductor
- B. A standard ammeter connected in parallel across the feeder
- ✓ A clamp-on ammeter placed around one feeder conductorCorrect
- D. A megohmmeter applied conductor-to-ground with the feeder energized
Why C is correct
A clamp-on ammeter reads current inductively around a conductor without breaking the circuit, making it the correct tool for measuring load current on an energized feeder. Connecting a standard ammeter in parallel across a voltage source would drive a destructive short-circuit current through the low-resistance meter movement. A voltmeter in series would block current flow.