WiremanWireman · Half the house is out: troubleshooting for electricians · 2023 NEC ·
Half the house is out
Some circuits dead, others fine, and 240 V appliances won’t run. Usually a lost leg.
Before you start
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How it works
A home gets two hot legs (L1 and L2) and a neutral. Each leg feeds every other breaker space, and 240 V loads use both. If one leg is lost, half the 120 V circuits die and every 240 V load stops or hums. If the lights are bright in some rooms and dim in others instead, that’s a neutral problem, which is more dangerous.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What do you see?
- Some circuits dead, others work normallyTest: Measure at the main breakerExpect: About 120, 120 and 240 V on both sides.
- Line side missing a legLost leg from the utility
- Line side good, load side missing a legA failed main breaker
- Both sides goodThe problem is at the branch breakers
- Legs read unequal, like 150 / 90Open or loose service neutral
- Some lights very bright, others dimOpen or loose service neutral
- Only one appliance (dryer, range, A/C) won’t workTest: Measure at the appliance’s breakerExpect: About 240 V.
- 240 VThe supply is fine; the appliance has a fault
- About 0 V or 120 VOne pole of the 2-pole breaker isn’t passing power
- Some circuits dead, others work normallyTest: Measure at the main breakerExpect: About 120, 120 and 240 V on both sides.