Question 68 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is C ### Explanation of Correct Option (C) Option C ("The live-line tester should be checked by connecting to a known high voltage source before and after the circuit to be worked upon is tested.") is correct because it describes the mandatory safety procedure known as the "Three-Point Test" or "Test-Before-Touch and Test-After-Touch" (proving dead). 1. **Test Before (Test-Before-Touch):** The tester must be verified immediately before use (by connecting it to a known live voltage source) to ensure it is functioning correctly and can detect the voltage that is expected to be present. This proves the tester is capable of detecting voltage *before* it is relied upon to prove the circuit is dead. 2. **Test Use:** The tester is then used to check the circuit being worked upon, confirming it is dead (zero voltage detected). 3. **Test After (Test-After-Touch):** The tester must be verified immediately after use (by connecting it back to the known live voltage source) to ensure the tester did not malfunction or fail during the proving dead procedure. If the tester had failed during the process, the preceding "dead" reading would be unreliable, necessitating a retest with a verified device. This dual verification process (before and after) is a critical safety requirement to ensure the integrity of the "prove dead" procedure, minimizing the risk of accidentally contacting a live conductor. ### Explanation of Incorrect Options **A) The live-line tester need not be checked prior to testing the circuit to be worked upon as long as it has not been declared inoperative.** This is incorrect. Relying only on the previous operational status is dangerous. Testers can fail unexpectedly (e.g., due to internal damage, battery depletion, or component failure) between uses. Verification against a known live source immediately before use is mandatory to ensure functionality. **B) The live-line tester should be checked by connecting to a known high voltage source only before testing the circuit to be worked upon.** This is insufficient. While the "test before" step is crucial, the "test after" step is equally necessary. If the tester failed *while* proving the circuit dead, the preceding zero reading would be invalid, and the operator would not know it. Testing afterwards ensures the device maintained its integrity throughout the process. **D) The live-line tester should be checked by connecting to a known high voltage source only after testing the circuit to be worked upon.** This is dangerous and fundamentally flawed. If the tester is only checked *after* the dead test, and it is found to be functional, the procedure is incomplete. More critically, if the tester failed *before* or *during* the dead test, the operator would have incorrectly confirmed the circuit was dead and potentially risked contact with a live circuit. The initial verification (test before) is essential.