ELCB, RCB and RCD Circuit Breakers :
ELCB: Earth Leakage Circuit Breaker
ELCB stands for “Earth Leakage Circuit Breaker” and it is used for
protecting a person from electric shock and injury. The needs of these
devices arise because of the number increasing in injuries as well as
deaths because of electric shock. This device is invented almost 50
years ago, but nowadays ELCB is not suitable because of its some
disadvantages hence another device RCB (Residual circuit breaker) or RCD
(Residual Current Devices) whose functionality is same with more
advantages, but theory of operation is entirely different from ELCB.
ELCB Construction:
It is international standard that each electronics device enclosure
should be earthed. So, there would be no chance of electrocutions. For
proper operation of ELCB, its need to bury a metallic rod deep in the
soil and ELCB is connected between the wire coming from the rod to the
wire attached to the external metallic body of the Electrical device or
you can say that ELCB is connected to the Earth wire.
ELCB Operation:
When the live wire (accidentally) touches the metallic body of the
connected device or appliance, then there is potential generated between
the earthed rod and the metallic enclosure of that device. The
circuitry (inside the ELCB) senses the potential difference and when
this potential difference reached at 50volt then ELCB cuts off the main
supply from the connected device. This way it ensures the safety of the
human beings.
However, it is not used widely nowadays because of its some major disadvantages which are
Disadvantages of ELCB:
- Without proper earth connection, ELCB will not work. If the wire attached to the earthed rode is loose or broken, then ELCB would not able to sense the potential hazardous voltage on the metallic body of the electrical/electronic device.
- ELCB is attached between earthed wire and metallic body of the electrical appliances. But there are many other parallel paths for the currents to flow from the connected device body to earth without going through earthed wire. E.g. there are many metallic pipes in the house, which can provide a parallel path for the current to flow towards the earth. In this way, sometime ELCB is not able to detect the hazardous voltage on the metallic body of the device, which may cause serious injury.
- If someone gets in touch with live phase wire, ELCB will not Trip because in this case, there will be no current flow in the earth wire. In fact, current is flowing from the live wire to earth through the person’s body.
- When a live wire comes in contact with neutral wire, short circuit will occur, hence, ELCB will not trip because there will be no current in the earth wire.
- There are many cases in which, there is a current flow in the earth wire, but the situation is not hazardous in such cases, but it gives false trip e.g. lightening strike, current starts flowing in the earth wire and ELCB trips.
To overcome with the above disadvantages of ELCB, another Device
named Residual Current Breaker (RCB) is invented to use for earth
leakage protection.
RCB and RCD
Residual Current Breaker (RCB):
Residual Current Breaker (RCB) works on the assumption that the
current going to the electronics device must come out from the neutral
wire, if there is no other way for current flow. In simple words, RCB
measures the current going inside the connected device and coming out
from the device. If both of these current are equal, then there would no
problem with the normal functionality of the device.
This device is also known as Current Operated ELCB.
This device is more sensitive and accurate than ELCB and its
functionality does not (entirely) depend on the earthed rode wire
connection like voltage ELCB.
Working of RCB or Current Operated ELCB:
The polarity of the phase winding and the neutral winding is
opposite in normal condition. Therefore, EMF generated by the phase wire
cancels out by the EMF of the neutral wire. If there is a difference in
the incoming and outgoing currents, then the resultant EMF will not be
zero and can be sensed by the CT of RCB. The signal from the RCB current
transformer is fed to the RCB circuit and it opens the main power
contacts.
Advantages of RCB:
1) If there is no connection between the ground and the enclosure
of the device, and a person touches the metallic body of that device. In
this case, incoming and outgoing current will be different and RCB will
Trip in contrast with ELCB.
2) Functionality of RCB (Residual Current Breaker) does not effect by lightning strikes.
3) It does not trip falsely.
