Make a Simple Earth Leakage Circuit Breaker (ELCB) Circuit


An Earth leakage circuit breaker unit will silently monitor the
electrical condition of your appliances and the Earth connection of your house.
If anything goes wrong with them it will instantly switch off the mains and
stop any further associated loss. A simple ELCB circuit is discussed here.


A simple circuit of an Earth leakage circuit breaker also called
ground fault circuit interrupter is discussed in this article. The circuit once
built and installed will silently monitor the “health” of the earth connection
of your house and the connected appliance. The circuit will immediately switch
off the mains on detecting a missing earth connection or a current leakage
through the appliance body.
A leaking
current through earth terminal is probably more dangerous than a short circuit
in a domestic wiring. A short circuit hazard is visible and mostly tackled
through a fuse or a circuit breaker unit. But earth current leakages may remain
hidden for years, eating up your precious electricity and also weakening or
deteriorating the wiring conditions and also the appliances. Moreover if the earth
connection is not properly grounded due to improper conduction or breakage, the
leakage may turn into a lethal shock over the body of the appliance.
Commercially available earth leakage
circuit breaker units are very costly and bulky, involving complicated
installation procedure. I have designed a simple circuit which is low in cost
and yet handles the situation handsomely. The device will detect any current
exceeding above 5mA through the earth passage and switch off the mains. The
connected appliance will then need a diagnose or a total elimination. A leaking
appliance not only wastes your electricity but also can be dangerous fatally.
Circuit Description
The
proposed ground fault circuit interrupter or ELCB utilizes a simple principle
of detecting the AC signal rather the applied or the leaking voltage. Here, the
leaking AC may be too small to be detected as a potential difference using
simple voltage detection configuration, therefore the leakage is effectively
sensed as a frequency, using a simple audio amplifier stage.
 As shown in
the diagram, a simple bootstrapped amplifier network forms the main sensing
stage of the unit.
Transistors
T1 and T2 along with the associated passive components are wired up into a
small two stage amplifier. The introduction of R3 becomes very crucial as it
provides a positive feed back to the input making the circuit more stable and
respond to minutest input signals.
The
inductor L1 basically has two windings, the primary which is connected to the
earth point of the socket has less number of turns, the secondary winding has
six times more number of turns and is integrated to the input of the circuit
via C1.
The role
of L1 is to amplify any AC induced into its primary winding which can only
happen in case of a leakage through the body of an appliance connected to the
socket.
The above
amplified leakage voltage is further amplified to a level enough to activate
RL1, instantly disabling the input to the appliance and indicating the earth
leakage fault.
Capacitor
C5 along with D3 and C4 forms a standard transformerless power supply to power
the circuit. D3 performs a dual function of rectification and surge
suppression.
Interestingly
the main earth connection itself becomes the negative of the circuit instead of
the neutral line. Also since RL2 is directly connected to the supply across the
positive of the circuit and the earthing, simply means that if the earthing
becomes weak or disconnected, the relay will deactivate, cutting off the AC
mains to the appliance, so it effectively indicates the health of the earthing
and safeguards the house from faulty or missing earth connections.
ELCB Circuit Parts List. 
R1 = 22K,
R2 = 4K7,
R3 = 100K,
R4 = 220E,
R5 = 1K,
R6 = 1M,
C1 = 0.22/50V,
C2 = 47UF/25V,
C4 = 10uF/250V,
C5 = 2UF/400V PPC,
T1, T2 = BC 547B,
T3 = BC 557B,
Relays = 12V, 400 Ohm, SPDT,
All Diodes are = 1N4007,
L1 = Coil wound over a bobbin used normally with E-cores (smallest size,) begin winding 50 turns of 25 SWG wire first, tie it up and solder it to produce the primary terminals at one side of the bobbin. Now using 32 SWG copper wire, wind 300 turns over the primary winding, as before tie the ends to the other side of the bobbin by soldering. Insert and fix the coil within the E-cores. Secure it tightly using PVC tape