WiremanWireman · Generator runs but no power: troubleshooting for electricians · 2023 NEC ·
Generator runs but no power
Breakers, GFCI, then output voltage and frequency at the generator.
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How it works
A generator makes voltage by spinning a magnetic field past copper windings. On most portable and standby units, a voltage regulator (AVR) feeds the field, and the field needs a little leftover magnetism in the rotor to get started. The engine’s speed sets the frequency: a 2-pole generator turns 3600 rpm for 60 Hz and a 4-pole turns 1800 rpm. So “runs but no power” is either something open between the windings and the load, or the generator isn’t making voltage.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Are the generator’s own breakers on, and any GFCI receptacles on it reset?
- One was off or trippedGenerator breaker or GFCI was open
- All on, still no powerTest: Measure voltage and frequency at the generatorExpect: About 120 V (and 240 V across the hots), and close to 60 Hz. Many governed portables run a little above 60 Hz with no load.
- 0 VThe generator isn’t producing voltage
- Only a few voltsLikely lost residual magnetism
- Voltage OK but frequency well off 60 HzEngine speed is off
- Normal voltage and frequencyThe generator works; the problem is past it