Why have an rcd? Not sure what an rcd is? Well basically it is a switch that if there is an electrical fault it will turn off the electricity quicker than you can blink.

To the right is a picture of a "plug in" RCD.

Most modern consumers units (your "fuse box") have a wired in rcd. Other manufacturers of rcd's are available

RCD stands for Residual Current Device, (similar to but not exactly the same as an Earth Leakage Circuit Breaker, elcb works on voltage not current)  or if you are in America it is called GFI ground fault interrupter

Normally electricity (current) flows  down one wire (Live) and through a device (say a pump, after all this is a watergarden site) to make it operate and back again down a second wire* (Neutral) the Third wire you will find in a cable is the earth. The purpose of the earth wire is is to connect the casing of a device to earth, the theory being that if the live wire touches it, the fuse blows breaking the circuit.

But the problem is as most pumps have plastic casings. which does NOT conduct electricity if the Live wire becomes detached / damaged it has no where to go. So when the pump or water which it is in is touched it is now LIVE and so the electricity flows through who ever touched it, to earth at the least giving a very nasty shock, but more than likely KILLING who ever touched it.

In normal operation as previously stated electricity flows down one side and back through the other, there by being "balanced" if however it detects an "Imbalance" say the device (pump in this case) has a damaged cable and it is touched the electricity will flow to earth via who ever touched it. The RCD will detect this and switch off the current instantly saving your life. That is why you should always use an rcd.

A few points.

Always make sure that ANYTHING electrical you use has a secure but not damaged cable.

If you find a damaged cable on an appliance, get the cable changed DO NOT USE IT.

If it is a submersible pump throw the pump away DO NOT attempt to repair it. A pump may cost several pounds and can be replaced, A life is priceless and can not be replaced.

If you are not sure consult a qualified electrician.

*This the generally accepted flow of electricity but in reality it is reversed.

please also be aware of part p

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