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Mini consumer unit required for shower?

Postby jjppcc_1 » Wed Oct 08, 2008 5:57 pm


I am having a shower installed, the plumbing is done already and it now needs to be wired up.

It is already connected to a 45A switch outside the bathroom via a 10mm T&E cable and then runs from the switch to near the consumer unit via the same kind of cable, awaiting the final connection to the mains by the electrician.

I would like to have everything an he needs before I hire one, but I have a concern.

My consumer unit has only has limited switches which are all currently occupied(2x6A-Lights, 1x32A-cooker, 1x31A-Sockets, 1x16A-water heater, and 1x16A-Central heating)

The Unit is a Crabtree 63A RCCB (240v 2Pole 4293)

I Don't really know what any of that means but it is written on the unit.

Will I need a mini consumer unit for the shower? or could I replace either the cooker or water heater (which are never used) with a 45A RCD?

If a mini consumer unit is required would it need a spare switch in the main unit to be wired in to anyway? and what cable should I buy for him to connect the mini unit to the main one?

I know that's a few questions, but I welcome any help.

Many thanks
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Postby ericmark » Thu Oct 09, 2008 5:28 am

There are many options it seems today electricians favour a single point of isolation I have not found a regulation that says this must be so but most domestic electricians in order to be able to sign off work under Part P are members of originations which impose extra regulations. It is unlikely that a RCCB is both covering all circuits and 30ma and if you have spare ways i.e. redundant circuit for cooker and water heater one would first need to know:-
1) Are these circuits already protected by a RCCB of 30ma
2) If not will a RCBO fit the board
RCBO combines the function of a MCB and RCD together but are either longer or wider than a MCB and some boards can not accommodate the extra length.
The main problem that I see is who signs the installation certificate as designing the circuit?
We are looking at two different regulations and laws. The BS7671:2008 regulation allows for three separate signatures for design, installation, and inspection and testing. If you are submitting plans to local building control then there is no reason why you should not sign for design and installation and an electrician can sign for inspection and testing. But where the electrician is a member of a organisation allowing him to sign the completion certificate under Part P then he would need to sign for all three sections which of course he should not do unless he has really designed and installed the work as well as inspected and tested. He could of course have an assistance who under instruction has carried out his wishes and that assistance could be you but he would need to tell you what he wants not you work it all out and him just sign.
If you ask him to connect up yes he can do that and if you ask him to inspect and test yes he can do that and issue a test certificate but he can’t issue a completion certificate and he is not breaking any law it is you who will not have informed LCBC.
I realise many people have no intention of employing an electrician and want to do whole you themselves and I do not care it is on their backs but also many people don’t understand the rules and are quite surprised when they find they can’t get a completion certificate. They ask wrong question. i.e.
Q “Can you test and inspect and connect up my shower” A “Yes”
Q “Can you issue a completion certificate” A “No”
I know the LCBC do not issue a written you may start work letter in all cases so I as the electrician will accept your word that you have registered the work. It is not me who is breaking the law unless I say “I am registered and will issue the completion certificate”. Once I say that then I as the electrician become responsible for the completion certificate. If I as an electrician don’t issue a installation certificate then I may end up in court or if I don’t follow the rest of the regulations I may end up in court and not to issue a installation certificate would be daft as on that I enter limitations and can back heal much of the responsibility. There is a link to Part P in projects section I don’t know Scottish Law but although not Part P still has restrictions.
As to question as to cable between consumer units if in trunking, surface or conduit then 25mm double insulated singles to Henley block or twin and earth to master MCB if taken from consumer unit and size will depend on MCB size with 50A being about the biggest available and 10mm being rated 64 amp clipped direct I would say 10mm would be normal but also I would use at least 10mm bonding to main incoming earth.
The regulations require interpretation and not all electricians will read them in the same way. We should all work from the guides ... uides.html and if we do there should be at least some sort of level playing field but it is up to the person signing the paperwork.

Postby sparx » Thu Oct 09, 2008 9:57 pm

Hi, not much to add save for question about 'add-on' unit,
Ericmark, we are pointed at regs 537.1.3 & in particular537.1.4
the implication of single point of isolation comes from the:
'A' main linked switch or circuit breaker SHALL be provided as near as practicable to the origin every installation.
'A' being singular.
Although a note after reg 537.2.1.1 seems to allow some latitude,

kind regards,
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Postby ericmark » Sat Oct 11, 2008 10:50 am

May be my English but a statement “A door must be provide to enter the kitchen” does not mean you can’t provide two? To me the same applies with the regulation I read it as at least one isolator must be provided. Maybe I should buy the Welsh version and see what it says in that!

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