Is RCD Adaptor necessary?


I have a modern house which probably has an RCD distribution board. If so, is it necessary to have an RCD Adaptor for my electric mower, etc? How do I confirm that my distribution board has a built in RCD?
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If it does have and RCD on all socket circuits (quite likely, I agree) then, no, you don't need further RCD protection for using your mower etc.
You *might* want to get additional protection by using a 10mA RCD for the mower but you may find them a little difficult to buy and it still doesn't guarantee discrimination with the main consumer unit RCD so a fault may trip one or the other or both.

Look at it? :-)
If it has an RCD the usual arrangement is that there is a main 'incomer' switch which is non-RCD, just a switch and then there is a second 'big switch' at the other end of the consumer unit which is the RCD protecting the socket circuits. If it's a very new house built to IEE 17th edition standards then the main incomer switch may also be an RCD but in this case a 100mA time delayed one.
If your consumer unit doesn't match these descriptions then tell us what it looks like.
--
Chris Green


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snipped-for-privacy@isbd.co.uk wrote:

Bob
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The CU will say RCD somewhere on it if part or all of it is RCD protected. It will also have a test button to test the RCD and will tell you the rating of the RCD (30mA, 100mA etc). There "should" also be a sticker on the CU telling you that there is an RCD and that it should be tested quarterly. This is often missing.
Adam
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Thanks for your posts, Chris & Bob. Very helpful.
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Assuming you have *working* 30mA RCD protection for the socket final circuit, you do not need a plug-in RCD adapter.
I say working because they can fail - without you knowing. - Remain "on" - but fail to operate even by test-button (MK, Wylex) - Remain "on" - but fail to operate within spec, but do operate by test-button (MK, MG, Crabtree) - Stay "off" - complete failure and refusal to turn back on (some older MEM)
This is extremely rare - however it does happen. - Test the RCD/RCBO regularly via the test-button - Never drop any plug-in or in-line RCD, they are fragile mechanical devices
RCD can drift out of specification due to stiction alone hence the need for regular operation, rough handling can also cause problems.
In some circumstances it is worth using 110V power tools & transformer (55V-0-55V). Example would be up a ladder (30mA will throw you off).
I you ever use 240V anywhere damp (pumps, mowing) then you may want to keep your extra plug-in RCD.
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