How does an earth-leakage circuit breaker or ELCB work?

Answer 1

An Earth Leakage Circuit Breaker - ELCB for short - was the first name given to what is now called a Ground Fault Circuit Interrupter (GFCI) .

The early, original, type of ELCB was designed only to detect a current flowing in the safety "ground" or "earth" wire.

Why was that important?

If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the "hot" or "live" wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit's safety "ground" or "earth" wire.

It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit's "hot" or "live" wire should only return to the power station via that same circuit's "neutral" wire.

So, as a result of that basic fact, if any current isflowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently.

Many years ago, before today's electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called Earth Leakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would "trip" - meaning "operate" - to break the current supply to the circuits for which they were installed to protect.

The original type of ELCB did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the "missing current" may actually be flowing to ground via someone's body!

When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give.

In the US and Canada such devices are still commonly known as "GFCIs" or "GFIs" even though they have the additional "residual current detector" functionality, whilst in Europe and elsewhere the more accurate name of "Residual Current Detector" or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device.

Another answer [Note: this is actually a description of a GFCI, not of an ELCB.]

An ELCB works by comparing the input current in the "hot" line feeding a load and the return current in the "neutral" line coming back from that load.

If the return current is less than the input current by a quite small amount - usually only about 30mA or less (mA = milliamps, which are thousandths of an amp) - it means there must be a leakage current.

That very small difference between the input and return currents is what the ELCB is designed to detect and cause it to trip so as to break the flow of current to the load.As the name itself indicates, an Earth Leakage Circuit Breaker device always checks for any leakage of current. The leakage may be either to the "earth" or "ground" wire or to something else such as the user of the equipment that is being protected by the ELCB device.

Answer 2

No, only circuit breakers and fuses can provide protection from general short circuit fault conditons.

An ELCB is connected into the ground wire of an appliance. The designed use of an ELCB is specifically to detect if there is a flow of current more than a certain minimum value (a few milliamps).

Such a flow of current means there is a fault somewhere that is causing live electricity to reach any grounded metal parts - which should never be "hot" - either inside the appliance or on its outside, such as its casing.

If that fault condition occurs the ELCB operates to break the flow of current coming from the power service to the appliance, thus helping to prevent people from getting electric shocks from it.

GFCIs - also known as RCDs in Europe and elsewhere - are usually installed nowadays to do a similar job because ELCBs can only monitor the ground wire of an appliance but GFCIs are designed to monitor both the hot and the neutral wires in the cord supplying power to an appliance.

A GFCI is a much better and safer protection device because it is designed to detect any difference more than a certain minimum value - a few milliamps - between the amount of current flowing in the neutral wire compared to the amount flowing in the hot wire.

If such a fault condition occurs, which means some current (the "difference current") must be leaking away somewhere else - which could be through a person who is using the appliance - the GFCI operates to break the flow of current from the power service to the appliance, thus helping to prevent people from getting electric shocks from it.

For more information see the answers to the Related Questions shown below.

Answer 3

An Earth Leakage Circuit Breaker was the first name given to what is now called a Ground Fault Circuit Interrupter (GFCI) . The original type of ELCB or GFCI was designed only to detect a current flowing in the safety "ground" or "earth" wire.

If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the "hot" or "live" wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit's safety "ground" or "earth" wire.

It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit's "hot" or "live" wire should only return to the power station via that same circuit's "neutral" wire.

So, as a result of that basic fact, if any current isflowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently. Many years ago, before today's electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called Earth Leakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would "trip" - meaning "operate" - to break the current supply to the circuits for which they were installed to protect.

The original type of ELCB or GFCI did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the "missing current" may actually be flowing to ground via someone's body!

When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give.

In the US and Canada such devices are still commonly known as "GFCIs" or "GFIs" even though they have the additional "residual current detector" functionality, whilst in Europe and elsewhere the more accurate name of "Residual Current Detector" or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device.