CSLB C-10 Electrical ContractorSafety and TestingMedium
A qualified electrical worker is using a digital multimeter (DMM) to measure AC voltage on a live circuit. Before making any measurement, what is the MOST critical safety check the worker must perform on the DMM itself?
- AVerify the test leads are properly inserted into the correct jacks for voltage measurement.
- BConfirm the DMM is set to the correct range and function for AC voltage.
- CCheck that the DMM's display is functioning correctly.
- DEnsure the DMM has a fresh battery for accurate readings.
Show answer & explanationAnswer & explanation
Correct answer: A. Verify the test leads are properly inserted into the correct jacks for voltage measurement.
Incorrect lead placement (e.g., in current jacks while measuring voltage) can create a direct short circuit across the voltage source, leading to an arc flash, explosion, or severe injury. This is a critical safety check prior to any measurement.
Why the other options are wrong
- B. Setting the correct range and function is important for accurate measurement, but incorrect lead placement is a higher safety priority.
- C. A functioning display is necessary, but incorrect lead placement poses a more immediate and severe safety hazard.
- D. A fresh battery is important for accuracy, but not the MOST critical immediate safety check for a live circuit.
DMM Lead Placement Safety
A critical safety check to ensure test leads are inserted into the correct jacks (e.g., voltage, current, common) on a Digital Multimeter before connecting to a circuit.
- Prevents short circuits
- Avoids DMM damage
- Protects the user from arc flash/shock
Memory trick: Jacks First, Then Function, Then Range!