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A GFCI outlet trips when the current going out and coming back differ by about how much?

About 5 milliamps, in as little as 1/40 of a second.

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  1. About 5 milliamps ✔
  2. About 15 amps
  3. About 1 amp

Why: A GFCI compares current on the hot and neutral wires. If about 5 mA is missing, it is leaking to ground, possibly through a person, so the GFCI cuts power fast.

Huh, didn't know that: A standard overcurrent breaker does not trip from a 5 mA imbalance alone; a GFCI is designed to detect that imbalance.

The dad joke
Why did the GFCI break up with the hair dryer? It sensed something was off.
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References

Answer: About 5 milliamps. A GFCI compares current on the hot and neutral wires. If about 5 mA is missing, it is leaking to ground, possibly through a person, so the GFCI cuts power fast.

  1. OSHA Construction eTool, Ground-Fault Circuit Interrupters www.osha.gov/etools/construction/electrical-incidents/ground-fault-circuit-interrupters
    When the amount going differs from the amount returning by approximately 5 milliamperes, the GFCI interrupts the current.
    Checked 2026-10-10.

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