ELCB working principle; Difference between ELCB and RCCB/RCD

Earth Leakage Circuit Breaker or ELCB

As clear from the name these circuit breakers are used for protection against electrical shock in case of leakage currents. ELCB get tripped whenever there are leakage currents in circuit. There are two types of ELCB’s:-

        Voltage ELCB

2.     Current ELCB

Now let’s discuss the same:-

1.   Earth leakage circuit breaker Voltage Type:-

As clear from the name these are voltage operated ELCB’s. These ELCB’s consists of relay coil. This relay coil is connected to the metallic body of equipment which is to be protected from earth leakage at one end and at other end it is connected to ground wire. If any fault occurs such as live wire touches the body than there will be voltage difference occur across the terminal of coil and earth. This voltage difference causes current to flow thus will operate relay and trips the ELCB. Voltage ELCB’s are available in various ranges these actuate as per limit described on ELCB’s.

Voltage ELCB’s are no longer used as there as following drawbacks:-

1.     These ELCB’s will disconnect the supply only incase there is fault between live and circuit earth. But these will not disconnect the supply if there are faults such as live part comes in contact with human body or live part comes in contact with water pipe etc. This happens because voltage across the circuit earth will not change.

2.     These ELCB’s not tripped even if there is fault between live and circuit breaker but there are parallel paths created other sources such as water pipes . As these cases ELCB get bypassed.

3.     These ELCB’s are used for protection of installation only but not the protection of human beings.

 

2.    Current ELCB’s:-

As clear from the name these ELCB’s operate on current leakages. These ELCB’s are most widely used in world. These ELCB’s are used for protection of both human beings and installations. These ELCB’s are used even when there is no earthing in installations. In general practice in electrical systems is that ELCB which are voltage based are known as ELCB’s and Current operated ELCB’s are known as RCD or RCCB. For principle and working of RCCB/ RCD please visit link as below:-

http://electrialstandards.blogspot.com/2014/05/residual-current-detector-principle-of.html

  

There is one advantage of ELCB’s over RCCB is that ELCB’s are less sensitive to fault current. In case of RCCB’s there will be some nuisance tripping.

Now days ELCB doesn’t exist in-fact RCCB is known as ELCB.

RCCB are used in House wiring also for protection of human beings from shock in case of any leakage currents.

Difference Between ELCB and RCCB:-

Even though ELCB doesn’t exist and now days RCCB is known as ELCB but in electrical systems there are following differences between ELCB and RCCB:-

1.     RCCB is current operated ELCB and ELCB is voltage operated ELCB.

2.     RCCB are used for protection for both Human beings and Circuit but ELCB is used for protection of Circuit only.

3.   RCCB used for detection of ay earth fault but ELCB are used for detection of earth faults which flows back through the main earth wire.

4.   RCCB has only line and neutral connections but in ELCB earth wire is connected through it.

 

RCCB ratings is usually in mA’s.

Human body can sustain electrical shock with magnitude of 30mA. RCCB in low voltage protection are designed such that they can trip off the circuit even for small currents upto 30mA. RCCB response time is usually in mSec’s. Thus RCCB will ensure protection of human body from electric shock.

Higher Range RCCB are also available in the market but these are used for protection where there is protection from fire hazard is sought. These are used where there is lot of flammable material is stored.

For houses RCCB range is Selected as 32-63A RCCB of 30-100 mA.

RCCB available in Market are 2 Pole and 4-pole.

2- Pole for Single Phase supply and 4-Pole of 3-Phase power supply.

Residual Current detector principle of operation and uses

Residual Current Detector:-

Residual current detector works on the principle that amount of current flowing through phase should return through neutral as both phase and neutral are connected to RCD’s . RCD detects any mismatch between two currents that is through phase and neutral. RCD tripping value is usually in milliamp and mostly available in 30mA and 100 mA tripping range.

If a house has an earth system connected to an earth rod and not the main incoming cable, then it must have all circuits protected by an RCD

A current flow of 30 mA  is sufficiently small that it makes it very difficult to receive a dangerous shock. Even 100 mA is a relatively small figure when compared to the current that may flow in an earth fault without such protection.

The residual current device – principle of operation

The residual current devices monitor the current flowing in a circuit by means of a torroid, which is a small current transformer specially designed to detect earth fault currents. All live conductors will pass through this coil, the currents flowing in the live conductors of a healthy circuit will balance and therefore no current will be induced in the torroid. Live conductors of a circuit include all phase and neutral conductors. When an earth fault is present on a circuit, current will be flowing to earth through an abnormal or unintended path. This earth fault path could be through a person in contact with live parts .

The Technology behind the RCD’s

There are two types of technologies available in residual current devices:-

1.      Electromagnetic and

2.      Electronic

These both offer very reliable performance.

Electromagnetic devices use a very sensitive torroid, which operates the trip relay when it detects very small residual currents. These devices generally require no reference earth lead and are unaffected by temporary loss of supply, as the power to trip the device is derived directly from the fault current.

Electronic devices do not need such a sensitive torroid as electronic circuits within the device amplify the signal to operate the trip relay. However, these devices often require a safety earth reference lead to ensure that the device will continue to operate in the event of the supply neutral being lost. The power to trip the device is taken from both the fault current and the mains supply, enabling the overall size of the devices to be reduced.

Limitations of RCD:-
1. RCD are use-full only where there is standard form of waveforms and can't be used where non standard waveforms are generated from loads.
2. RCD can't provide protection against overloads. 
3. RCD's can't protect against overheating.
4. There is always problem of Nuisance tripping in RCD's . Sudden changes in load causes current flow in earth which will leads to tripping of RCD's.