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How does a Ground Fault Circuit Interrupt work?

The Home Inspector checks for GFCI outlets and breakers and determines if they are operable or not. But how does a Ground Fault Circuit Interrupt work?

A Ground Fault Circuit Interrupter (GFCI) is an electrical safety device designed to protect against electric shock and electrocution hazards caused by ground faults. A ground fault occurs when electrical current leaks from a circuit and flows through unintended paths, such as through a person's body or through water. GFCIs are commonly used in areas where water and electricity may come into contact, such as bathrooms, kitchens, outdoor outlets, and garages.

Here's how a GFCI outlet and breaker work:

  1. Sensing Current Imbalance: A GFCI continuously monitors the flow of current between the hot and neutral conductors of an electrical circuit. The hot conductor carries the current from the power source, while the neutral conductor completes the circuit back to the source. The GFCI compares the current flowing through the hot and neutral conductors. Under normal conditions, the currents should be equal.

  2. Detecting Ground Faults: If there is a ground fault, even a small amount of current flowing through an unintended path (like a person or water), it creates an imbalance between the current flowing in the hot and neutral conductors. The GFCI senses this imbalance, typically on the order of a few milliamps, and quickly interrupts the circuit to prevent electric shock.

  3. Interrupting the Circuit: When the GFCI detects a ground fault, it trips a built-in electromechanical switch, disconnecting power to the protected outlet or circuit within milliseconds. This rapid interruption of power prevents the flow of electricity and reduces the risk of electric shock or electrocution.

  4. Resetting the GFCI: After tripping, the GFCI outlet or breaker must be manually reset to restore power. This often involves pressing a reset button on the outlet or flipping the breaker back to the "on" position. Once reset, the outlet or circuit is ready for use again.

In summary, GFCIs provide an important layer of protection against electrical hazards by quickly detecting ground faults and interrupting power to prevent electric shock. They are a crucial safety feature in modern electrical systems, helping to reduce the risk of electrical accidents and protect people from harm.

How does a GFCI work?
This is a typical ground fault circuit interrupt outlet.


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