A residual current device(RCD), it is also called residual current circuit breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. RCDs are designed to disconnect quickly enough to mitigate the harm caused by such shocks although they are not intended to provide protection against overload or short-circuit conditions. Greegoo is also your partner of MCB, RCBO, SPD and circuit breakers distribution boards.
Protection Against electroction
The use of exposed, substandard, badly wired, wrongly connected or damaged equipment as well as frayed or badly repaired cables reduces the safety of an installation and inreases the risk of person receiving an electric shock.
Electrocution is a passage of current through human body, which is dangerous. The flow of current through human body effects vital functions.
A correctly chosen RCCB can detect small currents flowing to earth and reduces the risk of electrocution. Effect of electric current through human body has been well researched and following chart summarizes the results:
Effect of electric current through human body has been well researched and following chart summarizes the results:
However, electrocution should not be viewed in terms of “current” alone but in terms of “contact voltage”. A person gets electrocuted by coming in contact with an object that has a different potential from his/her own. The difference in potential causes the current to flow through the body.
The human body has known limits:
- Under normal dry conditions, voltage limit = 50V
- In damp surroundings, voltage limit = 25V
Against indirect contact
Over current protection devices like MCB are unable to act promptly on small earth leakage currents. To comply with wiring regulations the earth fault loop impedance in Ohms, multiplied by the rate tripping current of the RCD in amperes must not exceed 50.
For an RCD with a rated tripping current of 30mA, the maximum permissible earth fault loop impedance is calculated as follows: Zs (max) = 50 / In = 50/0.03 = 1,666
To be within zone of the IEC curve as shown above. It is necessary for the ELCB to operate within 50ms at 240 mA and 150ms at 80mA. Both these conditions are satisfied by 30mA ELCB
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