The most largely used residual current circuit breaker or the RCCB are 30 milli-ampere and 100 milli-ampere devices. The 30 milli-ampere RCCB’s current flow is sufficiently small, making it very hard to receive dangerous shocks. Even a hundred milli-ampere is a small figure relatively ac compared to that of the current that could flow on the earth fault with no such protection from the hundreds of amps. A 300 or 500 milli-amperes RCCB can be used in which only fire protection is needed such as the lighting circuits in which the risk of the electric shock is very small.

Characteristics of residual current circuit breaker

  • Both the neutral and phase line wires are being connected through the RCD.
  • It is tripping the circuit when there would be a current earth fault.
  • The amount of current that is flowing through the phase line need to return through the neutral.
  • It is detected by the residual current device or the RCD. Any mismatch between the two currents that are flowing through the neutral and phase are detecting by the RCD, tripping the circuit within thirty mA.
  • If a house would have an earth system that is connected to the earth rod and not the primary incoming cable, then it may have all the circuits protected by the RCD, as you may not be able to get the right amount of fault current in order to trip a MCB.
  • The RCDs are an excellently effective form of protection from shock.

RCCB Limitations

The standard electromechanical residual current circuit breaker are designed for the operation on regular supply waveforms and are not guaranteed to operate wherein the non-standard waveforms are being generated by loads. The most usual is the half-wave rectifier waveform, at times being called the pulsating DC that is generated by the speed controlled devices, computers, semi-conductors, and even the dimmers. The especially modified RCCBs are available to be operated on regular pulsating, AC, and many more.

Furthermore, the RCDs are not offering protection against the current overload. The RCCBs can detect an imbalance in the neutral and live currents. However, a current overload cannot be detected. It is frequently the cause of problems with the novices in replacing an MCB in a fuse box that has an RCB. This can be done in an attempt of increasing protection from shock. If a neutral-live fault occurs such as an overload or a short circuit, the residual current circuit breaker will not trip, and has a tendency of being damaged. In practice, the primary MCB for the premises will possibly trip, or the service fuse, so the situation will most likely not lead to catastrophe, but it can be inconvenient.

You can get an RCD and MCB in a single unit, known as RCBO. To replace an MCB with RCBO with the same rating is generally safe. In the nuisance tripping of the RCCB, sudden changes in the electrical load will cause brief, small current flow to earth, especially in your old appliances. Residual current circuit breaker is very sensitive and it operates very quickly they trip well when the old freezer’s motor switches off. Therefore, RCCB will help you with an effective protection from shock.