This is
design circuit that used to indicates the integrity of wiring
connections. It shows all the mains connections Phase, Neutral and Earth
connections are intact or not. The circuit is too small and can be housed in a
three pin plug case. This is the figure of the circuit;
The circuit is directly connected to mains to
monitor the status of the connections. Earth connection is a must in domestic
wiring to bleed current to the earth if the metal body of a device is
accidentally touched with the phase line. This circuit indicates
2. Red and Green LEDs OFF Phase or Neutral Break / Power failure
3. Red LED ON Phase and Neutral OK
4. Green LED OFF Earth line break
The circuit gets power supply through C1 and R3.
AC Capacitor C1 reduces the high volt AC to a safer level through capacitive
reactance. Resistor R3 limits the inrush current and R4 gives discharge path
for the stored current in C1 when the circuit is unplugged. Zener diode ZD
regulates the voltage to a safer level to protect T1 when it is off. Voltage
across ZD will be a square wave by the working of C1 and the voltage level
depends on the breakdown value of zener (9 volts). When a potential of 230 volt
is present between the phase and neutral lines, T1 turns on during the negative
half cycle of AC and Green LED lights indicating that Earth connection is
intact. This is because the base of T1 will be biased by the potential
difference between the phase line and earth. If the earth connection is not
intact, T1 will not get base bias and it remains off. Red LED lights during the
positive half cycle of AC due to the potential difference between the phase and
neutral lines. Enclose the circuit in a 3 pin plug and connect points A, B and
C to the phase, neutral and earth pins respectively. Plug it into the 3 pin
socket to test the wiring.
