How does a GFCI detect a fault?

How does a GFCI detect a fault?

• A. It senses an imbalance between current in the hot and neutral conductors and trips if there is a difference.
• B. It measures voltage across the circuit.
• C. It monitors insulation resistance.
• D. It detects overheating.

Answer: (A)

A GFCI detects a fault by monitoring the current that leaves on the hot conductor and the current that returns on the neutral conductor. In normal operation these two currents are equal, so no residual current exists. If a fault provides an alternate path to ground (for example, someone touching a live surface or any leakage to the earth), some current escapes and does not return through neutral. That small difference between the hot and neutral currents is detected by the device and it trips quickly to shut off power, reducing the risk of shock. This mechanism is specifically about leakage current, not about measuring voltage, testing insulation resistance, or sensing overheating, which are associations of other protective measures.

A GFCI detects a fault by monitoring the current that leaves on the hot conductor and the current that returns on the neutral conductor. In normal operation these two currents are equal, so no residual current exists. If a fault provides an alternate path to ground (for example, someone touching a live surface or any leakage to the earth), some current escapes and does not return through neutral. That small difference between the hot and neutral currents is detected by the device and it trips quickly to shut off power, reducing the risk of shock. This mechanism is specifically about leakage current, not about measuring voltage, testing insulation resistance, or sensing overheating, which are associations of other protective measures.