Definition – ELCB is a device that is used in electrical circuit to protect a person from an earth fault.

What is an earth fault – An earth fault occurs when a live wire touches the body of the equipment (due to insulation failure etc) which causes metallic bodyof the equipment gets charged. When a person touches the charged body of equipment, he will get shock &person may die. Therefore, function of ELCB is to trip/interrupts the circuit when live wire touches the body of the equipment.

Types of ELCB – There are two types of ELCB – A) Voltage operated ELCB & B) Current operated ELCB. The current operated ELCB is also called RCCB (or RCD)

  1. Working Principle ofvoltage operated ELCB–It consists of a voltage operated coil (called search/sensing coil), fixed & moving contacts. This coil has two terminals, one terminal is connected with the metal body of the equipment while other terminal is connected with the earth.

Under normal condition, the voltage between metal body & earth is 0V, hence ELCB carries the normal current of the load. When earth fault occurs, it means phase wire touches the metal body of the equipment, the metal body gets charged & leakage current flows from body to earth. The search coil gets voltage difference across its terminals& actuates its tripping mechanism & trips the circuit.If fault is temporary, we may switch on ELCB again, but if fault persists, then ELCB will not be switched on again and we will have to rectify the fault first, then ELCB can be switched on.

(Note – For a human being 30mA current is a safe current & beyond this current is harmful so ELCB must trip on or less than 30mA current.)

Selection of ELCB

  • It should be capable to carry the rated current of load,
  • Check ELCB is required for single phase or 3 phase load.
  • Check number of poles – SP, SPN, DP,TP, TPN, 4P where SP = Single Pole which means only phase wire will be connected, DP = Double Pole which means phase & neutral wires will be connected, TP = Triple pole which means three phases will be connected, 4P = Fore pole which means 3 phases & a neutral will be connected.
  • Fault current rating(in mA) on which relay should trip/interrupts the faulty circuit, for ex – 30mA, 100mA, 300mA etc

Ex – 40A DP ELCB with 30mA fault current.


  • To operate ELCB, proper earthing is required. ELCB will not work If there is no body earthing of the equipment.
  • ELCB works on metal body equipment,

(Note:-Due to above limitations ELCBs are not being used and should be replaced with RCCBs because earthing is not required for earth fault protection in RCCBs.)