EMC Question of the Week: April 4, 2022

Diagram illustrating a GFCI circuit that opens the hot and neutral connections when a common-mode current is detected on that wire pair

Ground fault circuit interrupters (GFCIs) interrupt the connection to the power source when they detect a

  1. significant current flowing on the ground conductor
  2. significant difference in the currents flowing on the two power conductors
  3. loss of the connection to one or both power conductors
  4. power current surge


The best answer is “b.” All GFCIs are triggered by detecting a difference in the currents flowing on the two power conductors. Most GFCIs found in homes trip when the difference is about 6 mA. 

Unlike a fuse or standard circuit breaker, a GFCI removes the connection to both the power and power-return wires. It is not necessary for a product to have a ground conductor in order to utilize a GFCI. A growing number of products that operate at voltages greater than about 50 Vrms utilize built-in GFCI circuitry.

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