Wireman · No power to the whole building: troubleshooting for electricians · 2023 NEC ·

No power to the whole building

Everything is dead. Find out fast whether it’s the utility, the meter, or the main.

Before you start

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How it works

Power reaches a building through the utility transformer, the service drop or lateral, the meter, and then the service disconnect. When everything is dead, the question is which of those is open. A wider outage is the utility’s. A blank digital meter usually means no voltage is reaching the meter, since most meters are powered from their line side. If the meter has power, the main breaker or service disconnect is next. When only half the building is out, it’s a lost leg, which has its own guide.

Step by stepFull flowchart

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

Are nearby buildings or streetlights out too?
- Yes, the area is outA utility outage
- No, just this buildingWhat does the meter show?
  - Display is blank or the dial is stillTest: Measure at the service disconnectExpect: About 120, 120 and 240 V on both sides (120, 120 and 208 V on a 208Y/120 V service).
    - Line side deadNo utility voltage at the service
    - Line side missing one legOne leg lost
    - Line side good, load side deadWhat’s the main doing?
      - It’s trippedThe main breaker tripped
      - It’s on, nothing on the load sideA failed main breaker or disconnect
    - Both sides good, but the panel is deadThis panel is fed from somewhere else
  - Display is onTest: Measure at the service disconnectExpect: About 120, 120 and 240 V on both sides (120, 120 and 208 V on a 208Y/120 V service).
    - Line side deadNo utility voltage at the service
    - Line side missing one legOne leg lost
    - Line side good, load side deadWhat’s the main doing?
      - It’s trippedThe main breaker tripped
      - It’s on, nothing on the load sideA failed main breaker or disconnect
    - Both sides good, but the panel is deadThis panel is fed from somewhere else
  - Meter missing, blanked off or taggedThe utility disconnected the service
- Can’t tellWhat does the meter show?
  - Display is blank or the dial is stillTest: Measure at the service disconnectExpect: About 120, 120 and 240 V on both sides (120, 120 and 208 V on a 208Y/120 V service).
    - Line side deadNo utility voltage at the service
    - Line side missing one legOne leg lost
    - Line side good, load side deadWhat’s the main doing?
      - It’s trippedThe main breaker tripped
      - It’s on, nothing on the load sideA failed main breaker or disconnect
    - Both sides good, but the panel is deadThis panel is fed from somewhere else
  - Display is onTest: Measure at the service disconnectExpect: About 120, 120 and 240 V on both sides (120, 120 and 208 V on a 208Y/120 V service).
    - Line side deadNo utility voltage at the service
    - Line side missing one legOne leg lost
    - Line side good, load side deadWhat’s the main doing?
      - It’s trippedThe main breaker tripped
      - It’s on, nothing on the load sideA failed main breaker or disconnect
    - Both sides good, but the panel is deadThis panel is fed from somewhere else
  - Meter missing, blanked off or taggedThe utility disconnected the service