We use a number of Three Pin Sockets in our home. It has three connections- Phase, Neutral and Earth. Earth connection is an important safety measure to bleed the leakage current if any from the device using. In a Metal bodied device, if there is current leakage, there is the possibility of shock hazard . So the Earth connection should be intact to bleed the leakage current. How can we check whether the Earth connection is intact or not. The AC Tester check will not give the result because there is no current in Earth line. No problem, this tiny circuit will confirm whether the Earth connection is intact or not. The Green LED lights if the earth connection is intact, otherwise not. It is too simple, and can be enclosed in a Three Pin Socket itself.
You need the following components
1. IN 4007 Diode – 1
2. 33K 1Watt Resistor – 1
3. 470 Ohms ¼ W Resistor – 1
4. 470K 1.4 W Resistor – 2
5. BC 547 Transistor – 1
6. 5mm Green Diffuse LED – 1
7. 3 Pin Plug – 1
How it works
No additional power supply is needed for the circuit. The Rectifier diode D1 and the 33K resistor connected to the Phase pin drops the high volt AC and rectifies to a very low volt DC. LED is connected to the Collector of T1. The Base of T1 is connected to the Earth pin via a 470K resistor. The Emitter of T1 is connected to the Neutral pin. Thus T1 acts as a switch to light the LED. If the Earth line is intact, Green LED lights, otherwise not.
Warning! This circuit uses 230 VAC and exists at Lethal potential that can give a Fatal shock if touched. Build this circuit only if you are competent to handle high volt circuits. If you are a beginner and not familiar with AC circuit, leave this for safety.
Take all adequate safety measures during its testing. Test only after closing the case. Troubleshoot only after removing from the Mains.
The circuit uses the voltage appearing across the Earth and Neutral terminals when the circuit is connected. When the wiring is proper, a potential difference develops between the Neutral and Earth lines and T1 turns on to light the LED.
This how the Three pin plug and socket should be wired
No PCB is needed for the circuit. You can solder end-to-end. It can be enclosed inside the 3 pin Plug. Provide sleeving for the terminals of the components to avoid short circuit. Test the circuit only after fixing the case of the Plug.
1. The Anode of IN4007 Diode should go to the Right pin ( Phase ) of Plug
2. Base of T1 should go to Earth pin through 470K resistor
3. Emitter of T1 should go to the Left pin ( Neutral ) of Plug
LED lights . The three pin socket has intact Earth line
LED off . Earth line not intact ( Earth connection removed from the socket for testing )
Caution: This circuit uses high volt AC and there is Shock hazard if handled carelessly. Do not troubleshoot when connected to mains. Test only after fixing the cover of the 3 pin plug.