More than one RCD !?

1 Apr 2006
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United Kingdom
Inside the consumer unit I have a 30mA RCD and my question is, is there any advantages (or regulations meaning you are forced to) have additional RCDs to protect things like an electric garden strimmer or a shaver socket in a bathroom ?


I am going to get a Grohe Wireless shower system connected in a cuboard (next to the bathroom) to our ring main. The manual says it just needs a 3A fused switched spur (no mention of an RCD) - should it have one ? If so what is the order of connection is it:

Shower - RCD - 3A Spur - Ringmain
Shower - 3A Spur - RCD - Ringmain

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Your shower will be rcd protected if your comming off the ringmain, thats assuming the 30mA rcd you have in cu covers the sockets.
So ringmain socket > 3amp fcu off ringmain > shower

As for any more rcds not a requirement unless you have a TT earthing system then the prefferred method is a 100mA s type as main switch then 30mA for sockets etc, or the not so prefferred method of one 30mA rcd as the main switch but this entails all sorts of hinderances for the occupier.
plug the strimmer into the socket you would normally use. check that it works. Press the "Test" button on the RCD in your CU. Check that power to the strimmer socket is now off.

If so, the socket is protected by your RCD and you do not neeed another.

If the strimmer socket is still live, then you need another RCD.
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IMO it doesn't really matter if you have 2 RCDs inline like this, the regs don't like it as they won't discriminate but if I were getting a shock I'd rather have 2 RCDs upstream than none at all.

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