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Topic Title: Using an RCD as the main switch!
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Created On: 10 July 2008 01:39 PM
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 10 July 2008 01:39 PM
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rfc

Posts: 58
Joined: 25 March 2007

Hi All...
Been to look at a job today, a small house which will need a new consumer unit along with Tails, earthing(pme) and bonding..
There are five circuits..
1 Shower
2 Cooker
3 Sockets
4 Lighting
5 Immersion

I dont belive there will be need to add further cicuits in the future ( very small house)

I think i've read somewhere that I cannot use an Rcd as a main switch other than on a TT system.So installing a D/B with just a 30ma RCD acting as a main switch also is a not an option!

So do i

1. install a 16th edition type split load and put all 5 circuits on the Rcd side or
2. 17th dual split and lights and sockets on one side and cooker, shower and i/h on the other!
 10 July 2008 05:15 PM
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Tone322

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17th board with main switch, split load board, all circuits on RCD protection on both split loads (depending on depth of cables, mechanical protection, etc). Circuits must be split to provide safety in the event of tripping (ie upstairs and downstairs lights on differing RCDs).

An alternate choice is the use of RCBO's on each and every circuit. looking at the five circuits, I think after a thorough PIR and acceptable of the property I'd discuss the option with the property owner of using RCBO's in this instance and issuing an EIC.
 10 July 2008 05:22 PM
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Testit

Posts: 2962
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Well you could use a 100ma rcd for the main switch, and 30ma rcbos, discrimination and minimising inconvenience and maintaining safety is the issue
Contactum have a nice 8 way board for you http://www.tlc-direct.co.uk/Products/CPDS088P.html


and cheap rcbos http://www.tlc-direct.co.uk/Ma...e_MCB_RCBO/index.html

Personally I would leave some spare ways no matter how small when going to the expense of a new CU..

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Experience can sometimes show that cost prevails over quality and safety, such little self-value that people hold.

Edited: 10 July 2008 at 05:25 PM by Testit
 10 July 2008 06:10 PM
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OMS

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think i've read somewhere that I cannot use an Rcd as a main switch other than on a TT system.So installing a D/B with just a 30ma RCD acting as a main switch also is a not an option!


Two seperate issues I think.

1 - can you use the RCD as a main switch for the installation - yes, all RCCB's that meet BS EN 61008 are rated for isolation.

2 - should you be using a single front end RCD - again probably yes. BS 7671 imposes on a you a requirement to avoid danger and minimise inconvenience. This is a modest domestic residence where you would expect occupants to be familiar with thier environment. The more radical amongst us will dream up all sorts of scenarios including the skate board at the top of a stairs occupied by a pensioner to justify falling for the manufacturers ploy of selling split RCD boards or lots of RCBO's. Wiser heads may look at the situation and say that the hazards do not outweigh the consequences so the risk is low if you stick with a single front end device.

Consider what BS 7671 actually says - minimise inconvenience and avoid danger - so a single lighting circuit, single ring, single cooker and a single incoming service all fall foul of this reg.

Instead of twin RCD boards perhaps what we really need is duplicate incoming supplies with auto changeover and synchronised generators feeding into a crtical, essential and non essential installation reinforced by local parallel redundant UPS and significant diverse routing of circuits all installed in highly resiliant cabling - and we need it in every house in the country now.

Failing that stick in a 6 way board with a 30mA front end RCD and test and certify on completion.

Regards

OMS

Do it! It's easier to get forgiveness than permission

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Failure is always an option
 10 July 2008 06:15 PM
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rocknroll

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Instead of twin RCD boards perhaps what we really need is duplicate incoming supplies with auto changeover and synchronised generators feeding into a crtical, essential and non essential installation reinforced by local parallel redundant UPS and significant diverse routing of circuits all installed in highly resiliant cabling - and we need it in every house in the country now.


regards

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leave nothing but footprints!"
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"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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 10 July 2008 06:25 PM
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OMS

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What - a bit OTT d'ya think

OMS

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 10 July 2008 06:49 PM
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M107

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Only 5 circuits I'd go for RCBO's
 10 July 2008 07:37 PM
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rfc

Posts: 58
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Thanks for the replies, I've not long returned from the wholesalers with a crabtree 5+5 Split load board.Was only £25.00 + vat and I already have the mcbs so looks the most cost effective option...
Tomorrow I'll put the five circuits on the Rcd side and Blanks in the other unprotected 5 ways then its up to 17th and anyone wishing to maybe add a cicuit in the future can have the expense of buying an Rcbo.
Thanks again for replies
 10 July 2008 08:16 PM
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Jaymack

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I replaced a 4 way wylex with rewireables a few weeks ago with a dual RCD unit, this was in a small flat. The lighting, I placed on one RCD and the cooker, sockets and immersion heater on the other. This arrangement gave the best option IMO. 8 way DB total cost of £55 from via wholesaler from controlgear direct.

Regards
 10 July 2008 09:31 PM
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tillie

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OMS I like that idea.

Do you think I could still get away with installing rcbos?.

Regards
 11 July 2008 08:11 PM
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thedan71

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Originally posted by: rfc

Thanks for the replies, I've not long returned from the wholesalers with a crabtree 5+5 Split load board.Was only £25.00 + vat and I already have the mcbs so looks the most cost effective option...

Tomorrow I'll put the five circuits on the Rcd side and Blanks in the other unprotected 5 ways then its up to 17th and anyone wishing to maybe add a cicuit in the future can have the expense of buying an Rcbo.

Thanks again for replies


What's the difference between doing this and having a 30mA as the main switch. If one circuit has a fault, all the circuits will be affected. Haven't got my books infront of me, but I'm sure the reasoning behind sharing the circuits between more than one RCD or RCBO's is to stop all circuits being affected by a fault.

Dan
 11 July 2008 10:29 PM
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robsinders

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I cant see the point of using a split board with this set up, for the sake of another £20 why not put the lights on an rcbo?
 12 July 2008 06:07 PM
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ericmark

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Joined: 12 February 2008

I have seen very large caravans where two units are driven onto a base and are bolted together on site these will be feed from two RCD's in series both 30ma I can't see the difference between a very small house and large caravan except the latter is wired in flex. I think there are times when common sense should prevail.
Eric
 12 July 2008 07:40 PM
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Buz

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I rewired my house in 1991 using the MEM Memera 2000 consumer unit. This is fitted with a main switch which is an 80A mcb combined with a 30mA RCD so my whole house supply is permanently on a 30mA RCD which has been regularly tested. In 17 years I have only had about 6 nuisance trips (cause unknown). I have fridge freezers, a boiler and most other things that most houses have I suppose.

My point is that the total RCD solution may not be so bad?

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 12 July 2008 11:40 PM
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rfc

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"I cant see the point of using a split board with this set up, for the sake of another £20 why not put the lights on an rcbo?"
Exactly! ..£20.00.
I could understand if there were two lighting circuits or two socket circuits but there ain't so I'm £20 richer in my eyes..
All I want to do is play by the rules ( bs7671 )...I ain't into making up my own rules and I'm in this game to make money and £20 is £20.00 !
 13 July 2008 10:33 PM
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ChrisGilbert

Posts: 136
Joined: 12 January 2003

To me it's cheaper or not much difference to buy a twin RCD board than to buy a single RCD split-load one plus RCBO. RCBOs take up too much room and are a damn fiddle to wire up if they feed 6mm or greater. I am also going to start using the triple RCD boards from MK for certain multi circuit domestic jobs.
 13 July 2008 10:46 PM
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robsinders

Posts: 538
Joined: 02 July 2006

I could understand if there were two lighting circuits or two socket circuits but there ain't so I'm £20 richer in my eyes..


Or you could just add £20 to your quote and do a decent job .
Why bother with a split load board
Cut the tails and put a rcd before the existing fuseboard and you could save yourself a few more pence and have the same set up
 12 February 2011 09:36 PM
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cesltd

Posts: 124
Joined: 21 January 2009

I have a similar situation. A TT installation with a Hager board with a 60amp 100ma RCD main switch, all circuits controlled by MCBs. The garage has been converted, so 4 new circuits have to be added to the board. Do I just change the main switch to 30ma RCD, or add the 4 30ma RCBOs for each of the new circuits? If both are acceptable I suppose the main switch will be a fair bit cheaper.
 12 February 2011 10:01 PM
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RRichard

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This thread is over 3 years old & ideas and prices have changed. In an ideal world you should have a 100ma time delayed rcd up front and you need 30ma rcd protection for your new circuits if they have 13a sockets or cables buried less than 50mm .
 13 February 2011 08:13 PM
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MrOther

Posts: 539
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I like the idea of an RCD as a main switch, but with a Main Switch between the board and the meter instead of any blocks, this way any works on the board can be completed in total isolation.
IET » Wiring and the regulations » Using an RCD as the main switch!

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