CSLB C-10 Electrical ContractorSafety and TestingEasy
An electrician is troubleshooting a control circuit and needs to measure current. Which of the following instruments would be most appropriate for measuring current without breaking the circuit?
- AMegohmmeter
- BClamp-on Ammeter
- CDigital Voltmeter (DVM)
- DOhmmeter
Show answer & explanationAnswer & explanation
Correct answer: B. Clamp-on Ammeter
A clamp-on ammeter (or current clamp) is specifically designed to measure current by clamping around a conductor, allowing measurement without breaking the circuit or making direct contact with live parts, enhancing safety and efficiency.
Why the other options are wrong
- A. A megohmmeter measures high resistance (insulation resistance) at high voltages and requires the circuit to be de-energized.
- C. A DVM measures voltage, not current, and must be connected in parallel.
- D. An ohmmeter measures resistance and requires the circuit to be de-energized.
Clamp-on Ammeter
An electrical test instrument that measures current flowing through a conductor by detecting the magnetic field around it, without requiring direct electrical contact or breaking the circuit.
- Measures AC and/or DC current.
- Non-contact measurement, enhancing safety.
- Ideal for troubleshooting live circuits without interruption.
Memory trick: V-O-C-M: Voltage, Ohms, Current, Megohms – Each has its own tool.