Electrical and Energy

The typical consumer unit these days with the regulations now in place from the 17th edition changes require that circuits must be protected by RCD or Residual Current Device which immediately shuts down the system when there is any current leakage. The logic is that any current loss must mean a leakage, which could possibly be through a person to earth, which may cause death or serious injury.

There appears to be an argument at present as to whether the RCD actually protects against a current overload, which obviously has its problems as well. The Americans do often use a GFI or Ground Fault Interrupter or the RCBO or Residual Circuit Breaker Overload, which also trips on a current overload. I read an article where the person claimed that the RCD in fact provides a level of over current protection which although only basic is something to work with. 

The logic is that if you have a 100Amp 30mA RCD it will trip if the difference between the load on the live and neutral exceeds 30mA or if a 30mA or higher current is detected on the earth.

Also if the total load being passed through the RCD exceeds its maximum rating it will disconnect the circuit. The discussion is that a standard RCD will do this by electronic determination of the load current via the detection circuitry, which is not the same as the MCB or RCBO.

This argument is disputed and it would seem prudent to fit the combined residual current and over current protection units if there is a requirement for over current protection as well. This unit is known as the GFCI, Ground fault circuit interrupter in the USA and Canada or the RCBO, residual current circuit breaker with overload protection in Europe.

As well as requiring both line and neutral input the GFCI / RCBO devices require a functional earth connection. The units tend to be bigger than the RCD and space can become a problem. The GFCI units in the USA and Canada can be quite a lot more expensive. The units have not taken off in sales in Europe as they have in the USA but this may well be something which we can see coming into the regulations on the next inevitable revamp. It will certainly be one to watch and the no doubt the consumer unit suppliers will need to consider it in future.