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Residual Current Operated Circuit Breakers (RCCB technical information)

  • To open a circuit automatically in the event of an earth leakage between phase and earth and/or neutral and earth. With effective protection against human contact to earth points.
  • Protection against Direct Contact of persons or livestock with live part.
  • Protection against Indirect Contact of persons or livestock with exposed conductive parts which have become live under fault conditions.
  • Protection against Electrical Fires caused by high resistance fault arching but not causing the over current protection device to operate.
  • Designed with surge current withstand capability to prevent nuisance tripping during thunderstorms. Conditionally surge current proof (3000A, 8/20us), without time delayed tripping.
  • These devices are sometimes called an ELCB or RCCB or RCD.
  • Use in domestic, commercial and industrial installations.

Principle of operation

In the event of a short to earth the residual current operating system to prevent shock hazard voltage from remaining on the body of an electrical equipment. For this purpose, the residual current device monitor the difference between the loads flowing through it and ensures that it is aproximately zero. If, as a result of an earth fault, this difference exceeds the circuit breaker's residual operating current rating ln, then the RCCB will trip and disconnect the circuit of faulty equipment. (refer to Chart 1)

Additional protection in the event of direct contact

In order to provide additional protection in the event of a direct contact with (unearthed) live components, extremely sensitive RCCBs with a rated residual operating current of 30mA or less are used in place of more conventional RCCBs with higher residual operating current ratings.

This additional is necessary if :-

  1. The insulation of shockproof equipment or their leads is defective.
  2. The earth wire is interrupted.
  3. The earth and live wires have been transposed accidentally thus rendering live on the body of a device.
  4. A component which is live in normal operation is touched during repairs.

In the case of installation of equipment in areas with particularly high accident risk such as socket outlet circuits in bathrooms , power and lighting point for aquarium & fish pond. RCCB's with less than 30mA must be provided.

Since, in the event of direct contact, the residual current passes through the human body to earth and this additional protection should under no circumstances be regarded as a basic safety measure but acting merely as an "emergency brake" in the above mentioned electrical fault situations. (refer to Chart 2)

Fire protection

Even relatively insensitive RCCBs (In ≤300mA) can effectively safeguard against fires caused by earth leakage faults. In the case of residual currents ( ≤300mA) the electrical energy converted at the location of the earth fault is insufficient to ignite normal building materials. With higher residual currents, the RCCB will shut down in less than 100ms, thereby restricting the amount of energy released to harmless levels.

The use of RCCB on 3 phase 3 wires systems

The MAXGUARD range of 4 pole RCCBs can be used to provide residual current protection of 3 phase, 3 wire circuits (no neutral). Use terminal "1-2, "5-6", "N-N", otherwise the RCCB test circuit will not operate.

Selection of Type A RCCB is recommended to ensure compatible safe operation in the presence of pulsating dc components in the circuit. Household products using inverter power conversion technology needs to be protected with Type A RCCB for efficiency.