CSLB C-10 Electrical ContractorSafety and TestingMedium
A qualified electrical worker is using a DMM to measure AC voltage on a live 277V circuit. Before making contact with the circuit, which of the following is the MOST critical safety check to perform on the DMM?
- AVerify the DMM's battery level is sufficient.
- BConfirm the DMM is set to the correct resistance range.
- CCheck that the DMM's auto-ranging feature is enabled.
- DEnsure the test leads are free from visible damage and securely connected.
Show answer & explanationAnswer & explanation
Correct answer: D. Ensure the test leads are free from visible damage and securely connected.
Damaged or improperly connected test leads can expose the worker to live voltage or cause inaccurate readings, making this the most critical immediate safety check before contacting a live circuit.
Why the other options are wrong
- A. While important for accurate readings, a low battery is less of an immediate safety hazard than damaged leads when working with live voltage.
- B. Setting the DMM to resistance on a live circuit is extremely dangerous and can damage the meter or create a short circuit hazard. This is an incorrect setup, not a safety check.
- C. Auto-ranging is a convenience feature; verifying leads are safe is a more fundamental safety check than confirming this function is enabled.
DMM Pre-Use Safety (Live Circuit)
Before measuring live voltage with a DMM, ensure test leads are visually inspected for damage and properly connected to prevent electric shock or equipment damage.
- Inspect leads for cracks, frayed insulation.
- Confirm tight connection to DMM and probes.
- Prevents exposure to live voltage.
Memory trick: Leads are your lifeline, check them first!