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Difficulty: MediumProtective Devices

Complete the statement explaining the operational principle of a ground-fault circuit interrupter (GFCI) protective device.

Answer:A ground-fault circuit interrupter (GFCI) detects hazardous leakage currents by comparing the current flowing through the hot conductor with the current returning through the 【neutral】 conductor, tripping open if any imbalance indicates current escaping to 【ground】.

Answer

Blank 1: neutral; Blank 2: ground
A GFCI functions by using an internal differential current transformer through which both the energized (hot) and grounded return (neutral) conductors pass. When the circuit is normal, the magnetic fields generated by the equal and opposing currents cancel out. If current leaks to an external ground path (such as through damp ground, plumbing, or a human body), the magnetic fields no longer cancel, creating an induced voltage in the sensing coil that trips the breaker within a fraction of a second.

Step-by-Step Solution

1
Identify the paired current-carrying conductors monitored by a GFCI in a single-phase AC circuit.
Under standard closed-circuit operation, normal electrical current supplied by the hot conductor must return completely through the neutral conductor.
Kirchhoff's Current Law dictates that the outgoing current in the energized wire must equal the returning current in the neutral line in an intact circuit.
2
Determine where leaked current flows during a ground-fault condition to cause a trip.
Any difference between hot and neutral currents signifies that current has diverted through an unintended path (such as a person or equipment chassis) into the ground.
The differential sensing coil in the GFCI detects the magnetic flux resulting from the current mismatch and trips the internal switch contacts to prevent electrical shock.

Key Concept

Differential Current Sensing in Ground-Fault Protective Devices
Estimated Time:1m 0s
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Topics

Protective Devices

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