Help! RCD Keeps tripping on new wiring

I've bought from WF and Edmonson (ERD). I don't remember the exact price, but I'm pretty sure MK single way RCBO's were under £30 (particularly from my local WF which is an MK specialist/stockist).

Type C is unlikely to be a problem, particularly with RCD protection, although Type B is easy enough to come by and is what I would use on a domestic ring circuit.

Reply to
Andrew Gabriel
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My CU is a Memera 2000 and apparently I can add an RCD pod to the existing MCBs which will upgrade them to RCBOs - is it worthwhle to do this or should I just change the MCB for an RCBO, where I want RCD protection? I don't think there's much of a price difference.

Neil

Reply to
Neil Jones

You will find that the MEM RCBO you buy is simply an MCB and RCBO pod clipped together. If they do one in exactly the rating combination you want (not all variations are available preassembled), then you might as well go for it. Note that you are not supposed to disassemble the MCB and RCBO from each other once assembled, even if it is one you assembled yourself. (I've been tempted once or twice, but in the end never actually needed to.)

Also be careful as the Memshield 2 commercial range works the same way but they seem to have different MCB part numbers, so I would assume they aren't interchangable unless someone can confirm they are.

Reply to
Andrew Gabriel

On 7 Apr 2004 14:35:33 GMT, in uk.d-i-y snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) strung together this:

They are interchangable, it's the short circuit capacity that's the only difference AFAIK, 6kA for the Memera 2000 and 10kA for the Memshield 2.

Reply to
Lurch

Ah that makes sense, and indeed the Memshield 2 ones I have here are marked 10kA.

Reply to
Andrew Gabriel

Well I suppose it depends on arrangements, and whether you think all sockets circuits should be RCD protected. The installation I was thinking of actually had five RCD circuits - three rings (upstairs, downstairs, kitchen), one 20A radial (office in attic) and an electric shower. It had five non-RCD circuits, lights up and down, cooker, immersion and fridge/freezer. Actually the f/f socket was very accessible and so I gave it an RCD faceplate.

Well, not quite. Leaving aside Andrew's claim to have found RCBOs under

30 quid I am going to quibble with your figures. I've had a tiring day and need something daft to think about :-)

I have found Screwfix to be consistently cheapest for most things, and they have a few more things in cat 74 which fell through the door today. Let's do some comparisons for a ten-circuit installation:

Split load Volex kit, 12-way board, 10 MCBs - £60. The same board without MCBs, but including split kit - £49 (in cat 73 it is £60)

In other words, the MCBs are free in cat 73, but £1.10 each in cat 74. To buy them individually they are £3.79.

Split load Wylex kit, 12-way board, 10 MCBs - £75. The same board without MCBs, but including split kit - £55

In other words, the MCBs are effectively £2 each (£4.69 in the catalogue).

This, of course, ignores the possibility that you would need to swap one of the supplied MCBs for a differently rated one.

Now let's do it using RCBOs. Unfortunately, Volex RCBOs although £10 cheaper than Wylex ones are two modules wide so for the same number of circuits we need:

1 Service connector block - £6.70 2 extra sets of meter tails - £4.90 2 11-way Volex non split boards - £38 5 Volex RCBOs (almost fill one board) - £150 5 Volex MCBs (leave half the other board empty) - £19

Grand total: £218.60

The Wylex solution is simpler as their RCBOs are 1 module wide:

1 11-way Wylex consumer unit - £26 5 Wylex RCBOs - £200 5 Wylex MCBs - £23.50

Grand total: £249.50

So, far from being £100 different, the Volex RCBO solution is £158.60 more expensive than the simple split-load kit, and the Wylex is £174.50 more expensive (all bar a few pennies - I did some rounding of 0.99ps to £1s).

All round I think that usually the most appropriate solution will be a simple split load board, possibly with extra RCBO / local RCD protection of one or two circuits, which is what you suggested in your last sentence. This is what I am doing in my own house: three rings, one radial. The radial isn't on the common RCD, it's on an RCBO and feeds the utility room and an outside socket.

Thanks for letting me do that, I feel much more relaxed now :-)

Hwyl!

M.

Reply to
Martin Angove

On Thu, 08 Apr 2004 21:07:27 +0100, in uk.d-i-y Martin Angove strung together this:

[snip calculations]

But you could, on a new installation, have one RCBO protected circuit powering a collection of outside sockets at roughly each corner of the building, and that would be all that was needed. How much difference would that be then?

Reply to
Lurch

Well, that is nearly the same as I have suggested at the end of all that twaddle. The way I did it was to buy a Volex split kit for £60 and add a Volex RCBO for £30 - so total cost £90. It's not just outside sockets which need RCD protection remember, so it's not a simple case of buying a non-RCD board + MCBs for and just using a single RCBO :-)

Hwyl!

M.

Reply to
Martin Angove

On Thu, 08 Apr 2004 22:23:59 +0100, in uk.d-i-y Martin Angove strung together this:

In *most* installations then. RCD protection is required for portable equipment used outdoors, and occasionally other singular items inside which can usually be covered by an RCD spur. As with most things on here the actual end result after OT tangents is pretty much every installation differs, so there is no hard and fast rule! One thing I just noticed you missed from the original calculations was the need for a DP switch and enclosure to be able to isolate both boards from one point. So another £15 or so.

Reply to
Lurch

Absolutely. I was simply taking issue with the assertion that RBCOs is always "better" than MCBs protected by a common RCD. I was also pointing out that in all practical circumstances (i.e. more than one circuit on an RCD) using a common RCD will work out a lot cheaper. When you're talking about £40 for each extra RCBO, that's 10% of the total parts cost!

The fact is that in most installations it makes sense to have more circuits RCD protected than is the bare minimum, and the inginuity of the house owner is to be respected. For example, there is not normally a requirement for upstairs sockets to be RCD protected, but the house I was using as an example was built on a hill and, despite the presence of an outdoor socket near the back door I consider it highly possible that at some stage someone will string an extension lead out of the back bedroom window :-)

Hmmm... could turn into quite a mess of 25mmsq cables ;-)

Hwyl!

M.

Reply to
Martin Angove

On Fri, 09 Apr 2004 18:15:30 +0100, in uk.d-i-y Martin Angove strung together this:

Could do. Depending on the actual installation layout. Where possible I run a piece of 2x2 or 3x3 PVC trunking along the top or side of the two CUs and also across the top of the henley block and switch. All the cables are then hidden as they enter and leave the various switches, connections and CUs. Very tidy looking, it's exactly how I've got my installation setup at home.

Reply to
Lurch

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