WiremanWireman · 2-pole breaker passing only one leg: troubleshooting for electricians · 2023 NEC ·
2-pole breaker passing only one leg
The 240 V circuit has only one hot. Find out if it’s the breaker, the bus stab or where it’s installed.
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How it works
A 2-pole breaker clips onto two adjacent bus stabs that come from opposite legs, so it should give 120 V from each pole to neutral and 240 V across. It has a common internal trip, so a fault on either pole opens both. When only one pole passes power, the breaker has failed inside, one jaw isn’t making contact with its stab, or the breaker isn’t straddling two different legs.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Test: Measure at the breaker’s load terminalsExpect: About 120 V, 120 V and 240 V (208 V across on a 208Y/120 V system).
- 120, 120 and 240 VThe breaker is passing both legs
- One pole 120 V, the other 0 VTest: Check the bus stabs under the breakerExpect: About 120 V on each stab, and clean, bright metal.
- Both stabs 120 V, cleanThe breaker has failed inside
- A stab is burned or a jaw is looseA burned stab or a loose jaw
- A stab reads 0 VThe whole leg is missing at the bus
- 120 and 120 V but 0 V acrossBoth poles are on the same leg
- One pole reads low, like 30–80 VTest: Recheck the low pole with LoZExpect: About 120 V if the pole is good.
- Drops to about 0 VTest: Check the bus stabs under the breakerExpect: About 120 V on each stab, and clean, bright metal.
- Both stabs 120 V, cleanThe breaker has failed inside
- A stab is burned or a jaw is looseA burned stab or a loose jaw
- A stab reads 0 VThe whole leg is missing at the bus
- Reads a solid 120 VThe breaker is passing both legs
- Drops to about 0 VTest: Check the bus stabs under the breakerExpect: About 120 V on each stab, and clean, bright metal.