Electrical Wiring How Ground Fault Circuit Interrupters Work

Electrical Wiring How Ground Fault Circuit Interrupters Work GFCI-W JMA

GFCI’s A device that monitors the current flow in the two wires of a circuit. If there is a difference in the currents of as much as 5 millamperes the circuit opens. How is this done? The following principles are used.

When a wire is moved through a magnetic field a voltage is induced in the wire. Mo tio n V Mag netic F lux N S

When current passes through a wire a magnetic field is established. i

If the current changes with time, as with AC, the magnetic field changes with time. If a seconductor is placed in the changing magnetic field, a voltage is induced in the seconductor. i V

If the conductor is looped so that the conductor passed through the magnetic field twice the voltage induced is doubled. i 2 V

The more turns, the greater the voltage induced. For “n” turns the voltage is increased by n times what it would be with only a single conductor. i n. V

The direction of the magnetic field is dependent on the direction the current is flowing. If one grasp the conductor in the right hand, with the thumb in the direction of the current flow, the magnetic field is in the direction of the fingers. i

Current is from L to R Magnetic field is counterclockwise i i Current is from R to L Magnetic field is clockwise

If i 1 is equal to i 2 but in the opposite direction, then 1 is equal to 2 and also in the opposite direction. i 1 i 2 2 1

If we bring the two wires, with equal and opposite currents, very close together, then the magnetic fields cancel. A third wire placed near these two wires would not have a voltage induced. i 1 i 2 0 V

If I 1 is much greater than I 2, then the voltage induced is dependent on I 1. 1 i 2 2 ? V

If the two wires carrying the current for a circuit pass through a coil, consisting of many turns, no voltage will be induced in the coil if the current in each wire is the same. i 1 i 2 0 V

If one wire carries more current than the other then a voltage is induced on the coil, which is proportional to the difference in the currents I 1>I 2 i 2 ? V

GFCI’s These principles are used in the GFCI The two current carrying wires of a circuit pass through a coil, often called a current transformer. When the current in both wires are the same the output of the transformer is zero. If the difference in current is as much as 5 m. A, the output of the transformer is enough to trip a relay opening the circuit.

GFCI’s Line Current Transformer Latched Relay Load Electronics

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