Ground Fault Circuit Interrupter (GFCI)
GFCI is a device used to protect against electrical shock should someone come in contact with an energized wire and a path to ground. A GFCI detects the current between a hot and neutral conductor. Under normal conditions the currents are equal. However, if someone would accidentally come in contact with a hot and a path to ground, the currents are no longer equal. This will cause the GFCI to trip with-in a fraction of a second at a current of about 5mA, which is well below that which is considered dangerous to the human body. The lethal amount of current for a woman or a child is approx. 6mA, and for a man approx. 9mA.
GFCI's are for personal protection only, they are not for circuit overload protection. They should never be substituted for fuses or circuit breakers.
How does the GFCI know when to trip?
1. The current enters through the line side conductor, and is directed through the current transformer sensor (CT sensor), and then to the appropriate slot on the receptacle.
2. Once there is a load connected to the receptacle the current travels back using the neutral conductor and through the CT sensor again.
3. The electronic circuit compares the two currents going through the transformer sensor.
4. When the differential between the currents exceeds 5mA the solid state circuitry magnifies the current.
5. This causes the shunt trip solenoid to open the switching contacts and the reset button to trip.
6. With the switching contacts open there is no current able to flow through the circuit.
7. Once the reset button is manually pushed the switching contacts close and the circuit returns to normal.
How does the test button work?
1. Current enters through the line side conductor and bypasses the CT sensor up to the push-button.
2. When you manually push the test button, the push-button contact is closed.
3. The current continues through a resistor.
4. The current then returns through the neutral conductor passing through the CT sensor.
5. The causes the solid state circuitry to amplify the current.
6. This causes the shunt trip solenoid to open the switching contacts and trip the reset button.
The test button enables you to check that the CT sensor, the electronic circuitry, and the solenoid are all in proper operating condition. It is recommended that you test your GFCI's on a monthly basis.
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