Question 24 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is C **Explanation for Option C (portable low voltage high current testing unit):** Checking the calibration of a circuit breaker requires verifying the trip characteristics, particularly the instantaneous trip point and the thermal trip curve (for thermal-magnetic breakers). To do this, you must inject a controlled, precise amount of current—often several hundred or even thousands of amperes—into the breaker's primary circuit for a specific duration. A **portable low voltage high current testing unit** (often referred to as a "primary injection test set" or "breaker test set") is specifically designed for this purpose. It steps down the voltage and delivers the necessary high current required to accurately simulate an overload or short circuit condition and confirm that the breaker trips according to its manufacturer-specified curve and setting. **Why the Other Options Are Incorrect:** * **A) 500-volt megohmmeter:** A megohmmeter (or "Megger") is used to measure insulation resistance by applying high DC voltage. It is used to check the condition of the insulation of wires or windings, not the calibration or trip characteristics of a circuit breaker. * **B) clamp-on voltmeter:** A clamp-on voltmeter measures AC/DC voltage or current (if it's also an ammeter) in an operational circuit. While useful for general troubleshooting, it cannot generate the necessary high test currents required to force the breaker to trip and check its calibration limits. * **D) standard digital multimeter:** A standard digital multimeter (DMM) is used for measuring basic electrical parameters like voltage, resistance, and low levels of current (usually up to 10 or 20 amps). It lacks the capability to inject the hundreds or thousands of amperes needed to test the tripping mechanism of a power circuit breaker.