ELCB

 

Earth Leakage Circuit Breakers ELCB)

4.3 Earth Leakage Circuit Breakers (ELCB)

A human operator may come in a direct contact with a live wire or he may touch a metal-case of a leaky instrument. In either case, a current flows through the body of the operator to the earth. The amount of this current depends on the touch voltage and the human body resistance, which is a variable. A current exceeding a few tens of milliamperes through the body may prove to be fatal if permitted to do so for a long time. The Earth Leakage Circuit Breaker (ELCB) when installed in the electrical wiring protects the operator from such hazards. The ELCB is a safety device, which operates on low earth leakage current flowing in an electrical system. At such small currents, fuses or circuit breakers do not provide any protection, as they cannot operate till very high current flows in the wiring [6].

In USA and Canada, the same device (ELCB) is known as a Ground Fault Circuit Interrupter (GFCI) and in Europe it is called a Residual Current Circuit Breaker (RCCB). All these devices (ELCB, GFCI and RCCB) operate on the same principle [14].

In a typical wiring arrangement of an ELCB installation shown below (see Fig. 4.3 [6]), the live and neutral wires are passed through a magnetic core. Under the normal conditions, because the current in both conductors is equal and opposite, there is no flux in the core and the relay coil is de-energized. The electrical supply to the load equipment is not interrupted.

Under certain fault conditions (e. g. leakage due to a faulty insulation), the current in the live wire can exceed the neutral wire. This produces flux in the core. The secondary winding on the same core produces a voltage, which is amplified and applied to a relay coil. The relay operates and interrupts the live and neutral conductor. The earth leakage trip current can be pre-adjusted between 5 mA to 30 mA depending on the application in which it is used.

A typical ELCB is built into a 230-volt circuit breaker and is located in the panel board. A reset lever is provided on the ELCB to reset it after the cause of the leakage is detected and removed. A test button, if provided on an ELCB, can be pushed to check the functioning of the device as this action simulates an imbalance in the live and the neutral wire.

In the three-phase ELCB variety, the vector sum of the currents in the three lines and the neutral is continuously monitored. A nonzero current indicates a leakage in the wiring and the ELCB operates and disconnects all the supply conductors of the equipment [15].

The technical data of a typical ELCB device available in the Indian market is shown in the Table 4.3 [15] below:

 

Table 4.3: Technical Data of an ELCB

Specifications	BS 4293 – 1983/IS12640 – 1988
Sensitivities	High (30 mA)
	Medium (100 mA)
	Low (300 mA) Optional
Normal Voltage	2Pole 240 VAC 50 Hz
	4 Pole 240/415 VAC 50 Hz
Electrical Life	4000 operations
Mechanical Life	20,000
Connection Capacity	25/40 A – 16 sq. mm
	63/80 A – 25 sq. mm
	100 A – 35 sq. mm
Ambient Temperature Range	50C to 400 C
Degree of Protection	IP 30
Recommended Back-up HRC fuses	for 25 A & 40 A	80 A
	for 63 A, 80 A & 100 A	100A

Installation of an ELCB for a domestic environment and that for a number of equipment that performs a variety of unrelated functions in a field station can differ considerably. A tripping of a single ELCB need not bring to a halt the operation of the entire field station till the cause of the trip is located and rectified. For this, the equipment in the field station is divided in clusters and a separate ELCB is installed for each of them. This allows a majority of operations in a field station to continue in case an ELCB trips the supply to a group of equipment in a cluster.

ELCBs are available from following suppliers:

• Siemens Ltd., Bombay
• MDS Switchgear Ltd., Bombay
• Protect Switchgears Ltd., Vadodara.