WiremanWireman · Plug-in tester shows a wiring fault: troubleshooting for electricians · 2023 NEC ·
Plug-in tester shows a wiring fault
What each light pattern means, what the tester can’t see, and how to confirm with a meter.
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How it works
A three-light plug-in tester lights lamps between hot, neutral and ground, and the pattern shows open wires and some reversals. It can’t see everything. It can’t tell a real ground from a neutral jumpered to the ground screw (a bootleg ground), it can’t find a loose connection that only fails under load, and it can’t detect neutral and ground swapped with each other.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What does the tester show?
- Open groundIs it a 3-prong receptacle on old 2-wire cable with no ground wire?
- Yes, 2-wire cable with no groundNo ground wire to this receptacle
- No, there should be a ground hereA broken ground connection
- Hot/neutral reversedReversed polarity
- Hot/ground reversedHot and ground reversed
- Open neutral or open hotAn open hot or neutral
- Correct, but something still seems wrongTest: Measure all three pairsExpect: About 120 V hot to neutral and hot to ground, near 0 V neutral to ground, and hot to neutral dropping only a few volts under load.
- All normalTest: Look for a bootleg ground
- A jumper from the neutral, or a white wireA bootleg ground
- A bare or green wire from the cableThe receptacle tests correct
- Drops a lot under loadA loose or high-resistance connection
- All normalTest: Look for a bootleg ground
- Open groundIs it a 3-prong receptacle on old 2-wire cable with no ground wire?