Subpanel dead or partly dead

Every question and answer in this guide. Tap “Step by step” to walk through it.

• What do you see?
  • Everything in it is deadFind the feeder breaker in the main panel and the subpanel’s own main, if it has one. Is either tripped or off?
    • One was tripped, and it held when resetA tripped feeder or subpanel main
    • It trips againA fault or overload on the feeder or subpanel
    • Neither is trippedTest: Measure at the subpanel’s feeder lugsExpect: About 120, 120 and 240 V (208 V across on a 208Y/120 V system).
      • All normal at the lugsTest: Measure past the subpanel mainExpect: The same 120, 120 and 240 V as the lugs.
        • Normal past the mainPower reaches the subpanel bus
        • Missing past the mainThe subpanel main has failed
      • One leg missing or both 0 VTest: Measure at the feeder breaker in the main panelExpect: About 120, 120 and 240 V.
        • Normal at the feeder breakerA broken or loose feeder conductor
        • Missing at the feeder breakerThe feeder breaker isn’t passing one or both legs
      • Legs unequal, like 140 and 100An open or loose feeder neutral
  • About half dead, 240 V loads won’t runTest: Measure at the subpanel’s feeder lugsExpect: About 120, 120 and 240 V (208 V across on a 208Y/120 V system).
    • All normal at the lugsTest: Measure past the subpanel mainExpect: The same 120, 120 and 240 V as the lugs.
      • Normal past the mainPower reaches the subpanel bus
      • Missing past the mainThe subpanel main has failed
    • One leg missing or both 0 VTest: Measure at the feeder breaker in the main panelExpect: About 120, 120 and 240 V.
      • Normal at the feeder breakerA broken or loose feeder conductor
      • Missing at the feeder breakerThe feeder breaker isn’t passing one or both legs
    • Legs unequal, like 140 and 100An open or loose feeder neutral
  • Lights bright in some rooms, dim in othersAn open or loose feeder neutral