An earth leakage circuit breaker is a safety electrical device used for monitoring current leakages through the “earthing” terminal and switching OFF the mains when this leakage exceeds a certain dangerous level.
Normally electromechanical concepts are employed for making these devices, however here we will see how an ELCB can be made by using ordinary electronic components; we will also see why an electronic counterpart is more efficient than the commercial electromechanical units.
There are three versions through an electronic ELCB can be made, the first uses a relay for the switching actions, the second idea incorporate a Triac and the third concept employs a SSR or a solid state relay for the required implementations.
For all the above concepts, the triggering feature remains the same, through an input inductor stage.
ELCB Circuit Using Relay
Looking at the figure we can see that the entire circuit is concentrated around a single Opamp from the IC 324. The op amp is configured as a high gain inverting amplifier.
The op amp is configured as a high gain AC amplifier and its sensitivity can be adjusted by varying the value of R2, increasing its value increase the sensitivity of the circuit.
Any minute AC signal that may be present at the inverting input #2 of the IC is picked via the coupling capacitor C1 and instantly amplified by the IC.
A small inductor transformer is wired across the above input of the IC. The primary of the inductor is connected to the wire which finally terminates to the earthing terminal or the pin of the various 3-pin sockets in the premise.
The transformer can be an ordinary output transformer used in small radio receiver’s output amplifier stage.
In case of a leakage, the leaking current passes through the primary winding of the inductor and gets stepped up at the secondary winding.
The stepped up induced AC is immediately sensed by the IC input and further amplified to the desired levels, so that the SCR switches in response to the triggering.
The SCR, due to its inherent property instantly latches and pulls the relay into conduction.
The relay conducts and switches OFF the mains power to the three pin sockets, switching of the appliances and thus eliminating earth leakage conditions
ELCB Circuit Using a Triac
The above circuit can also be implemented using a Triac, everything remains the same, except the relay stage, which now gets replaced by a Triac.
During normal conditions the IC output remains switched OFF and the triac is allowed to conduct and operate the load.
However the moment a leakage is sensed, the IC output goes high, which triggers the SCR and latches its anode to ground. This inhibits the gate current to the triac which instantly stops conducting, switching OFF the load and rectifying the unfavorable conditions.
ELCB Circuit Using an SSR or SolidState Relay
Mians operated SSR devices are nowadays being effectively employed for switching mains operated loads more efficiently than relays and since these are electrically isolated and solid state in nature, becomes more desirable than the conventional switching devices like triacs and relays.
Here, as long as the conditions are normal, the SSR is able to derive the required input triggering voltage from the circuit, however the moment a leakage is anticipated, the circuit triggers the SCR which in turn chokes the SSR input trigger to ground. The SSR instantly stops conducting, implementing the intended actions by tripping the load and prevents any possible hazard.
R1 = 100K,
R2 = 1M,
R3, R4, R5 = 1K,
C1 = 0.01uF
C2 = 100uF/25V
L1 = ordinary small output transformer as used in transistor radios.
SCR = BT169
Triac = BT 136 or higher current type
Op amp = ¼ IC324
SSR = As per user specs.
Relay = 12V, SPDT