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Topic Title: RCD addition to lab socket ring
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Created On: 14 June 2018 12:14 PM
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 14 June 2018 12:14 PM
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tkerby

Posts: 71
Joined: 04 June 2002

Firstly to clarify this job will be done by an electrician. I'm fairly well versed in the regs as I've worked in related roles hence I know this needs to be fully certified as it's for public use. This is an is it possible question only

I'm part of a not for profit makerspace and we are based out of a building previously part of a university vetinary school. In each of our rooms we have multiple socket rings in plastic conduit supplied from the main distribution boards and wired with single core cables. The pair of LNE cables for each ring enters the room at a single point then connects to both ends of approx 10 double sockets in a length of the conduit. All the fixed electrics are tested and good.

What we would like is RCD protection for the sockets in our lab areas for added safety. At the moment plug in RCDs are available but not always used. Replacing all the sockets with individual RCD sockets would be incredibly expensive. The distribution boards can't easily be updated not can new cabling be easily run back to them from the labs due to the nature of the building. They're also in a locked room which is a problem if an rcd is tripped accidentally as we have 24h access to our space but couldn't reset an RCD.

What I'm wondering is whether it would be possible to take both ends of the ring from the distribution board in parallel, connect them into a garage type RCCB board and then run the ring locally to the sockets? That would give us local control and also provide a point we could shut off power to ensure all soldering irons etc were off when not in use.

Any thoughts on whether this is feasible or what the other options would be?

-------------------------
Tim Kerby CEng MIET

IET Council 2010-2013
Chairman, Scotland SE Young Professionals
 14 June 2018 01:09 PM
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broadgage

Posts: 2853
Joined: 07 August 2007

I would simply replace the sockets with RCD types.
This need not be "incredibly expensive" and might well be cheaper than modifications to the rest of the fixed installation.

Replacing each socket takes only minutes and involves no changes to rest of the installation.

Also, IMO, replacing the sockets could be done by anyone competent but not perhaps formally qualified.
Significant alterations really need proper qualification.
 14 June 2018 01:13 PM
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broadgage

Posts: 2853
Joined: 07 August 2007

Several fleabay sellers are offering RCD sockets for £10 each.
I doubt that the wiring could be modified in the way that you propose, for less than £100, the cost of ten sockets.
 14 June 2018 01:24 PM
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tkerby

Posts: 71
Joined: 04 June 2002

We are probably wanting to change this on all three rings that run in the main lab so about 30 sockets. If we avoid eBay and go with trade discount at CEF then it's about £17 per socket. We also need an electrician to do the work as it's part of the fixed installation and thus we need to keep the landlord happy. Comparatively it cost me around £180 to get my house fuse board changed over including a new board with RCDs and full testing.

We can get a quote for both but I'm wondering if it's feasible to double up the connections back to distribution and run the ring locally through an RCD. I'm trying to avoid someone coming in and seeing dollar signs and insisting on running an armoured cable back to the distribution as the last time we were quoted for that for three phase it was looking at about £3k. If it's allowable to make the modification to the existing circuits in the way I've suggested then it gives me an option to get priced up

-------------------------
Tim Kerby CEng MIET

IET Council 2010-2013
Chairman, Scotland SE Young Professionals
 14 June 2018 01:27 PM
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mapj1

Posts: 10914
Joined: 22 July 2004

electrically what you propose is perfectly possible, and is the sort of thing done to add mains filtering to labs and parts of them, while retaining the current capability for the ring. It is a non-standard arrangement and would need to be clearly documented along side as to what the RCD supplied and where it was fed from.
What is currently protecting the ring final circuit - if it is a fuse, then broadgage's comments will clearly be true,as the board will need to be changed, or a new one added. If it is an MCB however, it may be that an RCBO (combined MCB and RCD) is made that fits the box, and swapping it is a matter of half an hour. I appreciate it sounds like you'd then need key access Also, are there other loads on this ring apart from this one room ?
The other option that only involves work in the room is a half way house where nothing more than a couple of RCD fused spurs are actually on the ring, with each spur feeding then 2 or 3 double sockets.
Whoever does whatever is decided, needs to be competent and capable of testing it, but legally it does not require building works notification, or membership of any particular scheme, as it is not a dwelling. That said building insurers may insist on their own preferences.

RCD sockets
or spurs
are not very expensive compared to the cost of an afternoon's labour, and could be rolled out piecemeal as funds permit.


I have shown items rfom TLC, as I have an account, but
screwfix are simialr

-------------------------
regards Mike


Edited: 14 June 2018 at 01:43 PM by mapj1
 14 June 2018 01:47 PM
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broadgage

Posts: 2853
Joined: 07 August 2007

If you need 30 RCD sockets, they should be obtainable for about £10 each, even without resorting to fleabay.
Depending on your relationship with the landlords, I think that swapping socket outlets could reasonably be called "maintenance" or perhaps a simple "like for like replacement" rather than an alteration.

Do the landlords even know what type of sockets are fitted at present ?
 14 June 2018 05:33 PM
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Weirdbeard2

Posts: 449
Joined: 29 November 2017

Originally posted by: tkerby



What I'm wondering is whether it would be possible to take both ends of the ring from the distribution board in parallel, connect them into a garage type RCCB board and then run the ring locally to the sockets? That would give us local control and also provide a point we could shut off power to ensure all soldering irons etc were off when not in use.

Any thoughts on whether this is feasible or what the other options would be?


Hi Tim, sounds good to me, if as you say the cabling for the 3 rings all enter the room at the same position it should be fairly straight forward to fit an enclosure to house 3 decent double pole RCDs, the materials will cost much less without having to resort to buying the cheapest available RCD sockets, and also the monthly checking by pressing of the test button will be much more efficient doing 3 in the same place rather than walking round 30 sockets!
 14 June 2018 05:58 PM
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Legh

Posts: 4221
Joined: 17 December 2004

I'd prefer the localized RCD/MCB DB where the main DB is protected by Cartridge fuses.
S/C and Earth faults are picked up locally and rectified pdq.

Legh

-------------------------

http://www.leghrichardson.co.uk

de-avatared
 14 June 2018 07:04 PM
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Dave69

Posts: 733
Joined: 16 July 2011

Tim what you are suggesting makes perfect sense to me but why go to the expense of a garage board? You don't need a main isolator, just a double pole RCD in an enclosure or even just a plastic cover. About twenty quid from the wholesalers and if each ring is run in its own plastic conduit run then no more the 20 minutes to do each.

sixty quid materials and no labour costs if you do it yourself. Although it should take less than an hour I would imagine any sparky is going to charge you for at least two hours so that'll be another £90, still only £150 compared to well over £300 if you change all the sockets
 14 June 2018 07:14 PM
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chrispearson

Posts: 334
Joined: 15 February 2018

Originally posted by: tkerby

If we avoid eBay and go with trade discount at CEF then it's about £17 per socket.


I find CEF to be rather expensive.

Comparatively it cost me around £180 to get my house fuse board changed over including a new board with RCDs and full testing.


Originally posted by: Dave69

... any sparky is going to charge you for at least two hours so that'll be another £90 ...


Evidently Scottish labour charges are lower than further south.

One of the benefits of individual RCD socket protection is that one fault does not turn off the whole facility, but it does seem to be overkill. In answer to the OP, yes feasible, and I appreciate that under the circumstances DIY may not be appropriate. Why not get two or three quotes?
 14 June 2018 10:24 PM
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sparkingchip

Posts: 10836
Joined: 18 January 2003

My assessment is that 10 mA RCD protected sockets should be installed.

An additional advantage is that they trip if the supply is interrupted and will need manual resetting, preventing power tools and equipment restarting unexpectedly.

That should satisfy your risk assessment.

Andy Betteridge.
 15 June 2018 12:27 AM
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Alcomax

Posts: 324
Joined: 12 November 2009

As already suggested, you may only require on DP 30mA RCD instead of a "garage DB". Direct replacement with RCD socket outlet can have problems such as the the existing back box / cable management not able to accommodate the additional bulkyness of SRCD accessory.
 15 June 2018 06:54 AM
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ebee

Posts: 6503
Joined: 02 December 2004

"I find CEF to be rather expensive."
That is putting it very politely.

"Comparatively it cost me around £180 to get my house fuse board changed over including a new board with RCDs and full testing."
No way - that is far too cheap

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 15 June 2018 07:21 AM
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Nedryerson

Posts: 140
Joined: 12 December 2009

I would agree.

Direct Trade do a fully equipped Garage Board for £23.99 inc VAT.

Ned
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