RCD - Residual Current Device

On the left are the reset and test buttons. When the reset button is pressed, the relay will hold in and the lamp will light. On the right is a push button connected to a switchable resistor array and to the Live wire. This is to simulate someone touching the Live wire. When this is operated, there is a very small difference in the current flowing through the Live and Neutral wires. The difference is flowing through the resistor (person), to ground. Two current controlled voltage sources are used to monitor current in both the Live and Neutral lines. The voltage from each ccvs is fed into two op-amps, one of which inverts the signal. These two signals are then fed into a third op-amp where they are compared. Any difference in the comparison, results in an output from the third op-amp, which then trips the relays.

published 3 years ago