Earth Fault Indicator Circuit

Earth Fault Indicator Circuit

This circuit 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.

Earth Fault Indication Circuit Diagram

Earth Fault Indicator 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

1. Red and Green LEDs ON Phase, Neutral and Earth OK
2. Red and Green LEDs OFF Phase or Neutral Break / Power failure
3. Red LED ON Phase and Neutral OK
3. 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 rectance. 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.

Warning The circuit is kept at mains lethal potential. Do not touch any parts to avoid lethal shock. Do not construct this circuit unless you are experienced in handling High volt AC.


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  • bp sharma

    sir, may i add a circuit by that,if earth value less than 01 ohm then only green LED WILL GLOW.PL provide me same type of circuit. i want it most urgently.tks

  • vamshi krishna

    can any one comment the advantages and the regular application regarding this earth fault indicator

  • rajat

    both leds are glowing even when earth is not connected.
    circuit is ok
    earth gren led is glowing without earth connection?

  • cmesoar

    Second question: LED voltages are now all over the map – what voltage are you using here?

  • cmesoar


    You show R3 as 100R, does that mean 100 ohms? Likewise, you show capacitor C1 as 105K, is that 105 microfarads? Thank you for the clarification. As a point of reference, it might be useful to readers to see the pinout of a mains socket, ie which pin is supposed to be hot/neutral/ground…just a thought.

  • anjani

    why we use 1mega ohm resistor in seriies with the earth?

  • alyasaa miraji

    i have seen it thanx alot,what if i use 250V of a capacitor will the circuit function!?

  • puneet

    sir in my circuit only green LED on continue but red LED glows for very short time. Will u help me its urjents

  • Mamade Ibrahim Joomun

    If the Earth wire is unopened or unbroken but the Earth Loop Impedance is >500 ohms, will the GREEN Led lights?


  • Mamade Ibrahim Joomun

    Is it possible for the buzzer to energise (switch ON) when the Ground/Earth wire is opened from the circuit? Can a smoothing capacitor be added in the circuit to improve the sound quality of the buzzer? Can a capacitor X2 Class (0.22uF 275Volts AC) be used to make the device really miniature? Is it necessary to use resistors of 1 watt or 1/2 Watt is ok?

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