Hi Ten

What you have sound's like it may be a split-load board, where exactly in the board is the R.C.D Unit located?, the RCD unit will usualy be 2 module size, or the same width as two MCB's, if it's half way down the board, you have a split-load board, where half of the board is protected by the RCD, and the other half is unprotected

If all the ring circuit's/sockets are covered by this RCD, then there is no need to use a plug in RCD, except for you're own satisfaction..

The RCD in the consumer unit should be tested quaterly by testing the button marked 'T' or 'Test', this should cut off the supply to the circuit, it it fails to do this the RCD unit may be faulty and needs to be replaced

Thanks L.Spark & Beanzy for your responses. (I take it you meant me L.Spark - you called me Matt, my nick is Ten!)

Beanzy is correct - it isn't a consumer unit (my mistake, I researched the difference), it is a fuse box which I replaced the cartridge fuses with MCB's. The RCD could be retro fit but it looks like it was installed at the same time as the fusebox, the house was built (1987 ish). The RCD has a green sticker saying it protects the circuit shown on the fuse box. Below the MCB protecting the ring main is another green sticker saying "This circuit is protected by the RCD".
Any idea what year the regs first stated that any socket which could supply a feed to outside the home needs to be protected by an RCD? I'm not sure, perhaps I will take a look at a few of the other houses and see if they have the same.

Thanks for the advice - I will test to make sure the RCD is working correctly. For a periodic inspection, is it simply a case of phoning up a sparks and asking for just that? Any idea how much something like that would be for a small 2 bed house near Surrey/Hants borders?

Ten

Thanks again for the response L.Spark.

Interestingly, whilst researching further I came across this page on the web -

http://www.diyfaq.org.uk/electrical/consumer.htm

Which mentions that the RCD test switch is not just a mechanical trip out test, but creates an earth leak using a resistor. I guess if the RCD doesn't trip when the button is pressed then it really isn't protecting within specification and would not be a mechanical failure of the tripping mechanism.

Thought that might be of use, as long as it is correct of course.

Regards.

Ten.

OOI - question for all sparkies - what's the incidence of RCDs which trip when their test button is pressed but fail a proper test?

Out of how many seen/tested?

That's since I started the company about a year and a half ago, before that only did commercial testing with office and plant room stuff, didn't come across many RCDs, couple a year maybe. I have binned one without testing, but the green slime oozing out of it and the fact it was on a pole in a barn which had lost that part of it's roof about 4 years before made testing kind of superfluous

I'd be interested to see how my couple compare with everyone else. Just on a hunch basis I'd have said finding two in that time would be on the high side. I mean they should last for a decent span of use and they're normally tested on installation (though one of those I had can't have been). I can't imagine folks would be finding many failing to trip unless they fail mechanically.

Anyone else?

I've found exactly one RCBO that didn't work to spec in the last eighteen months. They seem to be extremely reliable bits of kit. Every plain RCD I've tested has worked fine.

In the case of this particular RCBO I quoted the miserly sum of £60 to supply and fit (the part was almost £50 onits own). The customer said he'd think about it... that was over a month ago; need I say more?