What is an RCD?

[Stargazer]

In connection with electricals? Also can I check to see if I have one? What does it look like and where may I find it please?

[boxtops]

It's a circuit-breaker - we've got one on the plug for the lawnmower, it kills the power if the connection is broken (e.g. if you mow over the cable).

[hc4361]

I have them in my consumer unit (used to be called a fuse box).
Good pic and explanation here
http://en.wikipedia.o...sidual-current_device

[The Builder]

Whereas MCBs (miniature circuit breakers) and wire fuses detect short circuit and overload (which may be a fault to earth, but not necessarily so) ..... RCDs only detect faults to earth.
They provide a good level of safety. A 32A MCB will need over 32A to operate, but a typical domestic RCD needs only a fault current of 30 milliamps (0.03A) to operate.

[The Builder]

If you can post a pic of your consumer unit and board, I could tell you if you have one.

[Stargazer]

Thank you for your advice. I can't post a pictire (I don't know how to) but can you tell me how much this unit is to buy and can it be fitted by an ordinary electrician (or does he need special credentials) also how many hours would you expect it to take and thus how much it might cost me? Is it illegal not to have this unit fitted? Also an earth spike. How much does it cost, how long to fit one and is this a legal requirements nowadays? Any advice very welcome and many thanks for same.

[The Builder]

This is an average example, Starry...............

http://www.google.co....HfBQ&ved=0CIQBEPICMAM

Look at your consumer unit carefully to make sure you don't have one.
The one in the link above, fits inside the CU next to the MCBs etc......... I doubt if you will have room to fit it though..................
In that case, I think the best bet would be to replace the main double pole on/off switch for an RCD. The RCD then serves as a switch as well.

A local electrician would take no more than 10 or 15 minutes to exchange them. I would strongly advise having an electrician to do this for you, partly because the CU contains live parts, and partly because he would know exactly which part to use.

If you had a re-wire, or it was a new house, today's systems must have RCD protection by law. It's not retrospective. You can't be made to have one.

[The Builder]

........... to make that a bit clearer ....... you can't be made to fit one on an existing, older system

Earth spike.......... I guess that's the earth rod?
If you need one, and you don't have it, then the system is dangerous and shouldn't be used.

There are a few different types of incoming supply. This is getting very technical now. In this country, only one type (a TT system) needs an earth rod.
Why do you ask?

[The Builder]

I've just seen your Q in Property........................

you didn't mention here that you'd been advised to have an RCD and earth rod fitted. Did this adviser say anything about Earth Fault Loop Impedance not being low enough?

[Stargazer]

Sorry Builder, but I have been away from this machine. I will reread your answers to my RCD unit and Earth spike queries and try to digest it all. It has arisen because of my quote for a new boiler by the British Gas. Because my existing boiler is still working, I have decided not to replace it at the moment because of the enormous costs involved.