WiremanWireman · Verify a circuit is dead (live-dead-live): troubleshooting for electricians · 2023 NEC ·
Verify a circuit is dead (live-dead-live)
Prove absence of voltage the right way: rated meter, every source locked, every conductor tested, tester proved before and after.
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How it works
A circuit is never dead because a breaker is off or a label says so. It’s dead when a working, properly rated meter shows no voltage on every conductor at the point where you’ll work. NFPA 70E calls this an absence-of-voltage test: prove the tester on a known live source, test every conductor phase to phase and phase to ground, then prove the tester again so you know it didn’t fail in the middle. It’s the last step of your lockout, done before anyone puts hands or tools on the conductors.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What are you going to test with?
- Non-contact voltage pen onlyA non-contact pen can’t prove a circuit is dead
- A multimeter or two-pole voltage testerIs the tester rated for this circuit?
- CAT III or IV, at or above system voltageTest: Find every source and lock it out
- Yes, all sources are lockedTest: Prove the tester on a known live sourceExpect: The voltage you expect from that source, for example about 120 V or 240 V.
- Reads the expected voltageTest: Test every conductor at the point of workExpect: 0 V, or under a volt or two, on every combination.
- 0 V on every pairTest: Prove the tester again on the known sourceExpect: The same voltage you read the first time.
- Reads correctly againAbsence of voltage verified
- Now reads nothingThe tester isn’t working
- Full or near-full voltage on any pairThe circuit is still live
- A few volts to tens of volts that driftTest: Check for ghost voltageExpect: A ghost reading collapses to near 0 V under the meter’s small load.
- Drops to near 0 V on LoZTest: Prove the tester again on the known sourceExpect: The same voltage you read the first time.
- Reads correctly againAbsence of voltage verified
- Now reads nothingThe tester isn’t working
- Voltage holds up on LoZThe circuit is still live
- Drops to near 0 V on LoZTest: Prove the tester again on the known sourceExpect: The same voltage you read the first time.
- 0 V on every pairTest: Prove the tester again on the known sourceExpect: The same voltage you read the first time.
- Reads nothing or a wrong valueThe tester isn’t working
- Reads the expected voltageTest: Test every conductor at the point of workExpect: 0 V, or under a volt or two, on every combination.
- Not sure, there may be another sourcePossible second source of power
- Yes, all sources are lockedTest: Prove the tester on a known live sourceExpect: The voltage you expect from that source, for example about 120 V or 240 V.
- CAT II, unmarked or too low a voltageThe tester isn’t rated for where you’re using it
- CAT III or IV, at or above system voltageTest: Find every source and lock it out