Kitchen Wiring (again)

[Demonic]

I am having a new kitchen fitted and have received some conflicting views from a couple of electricians so I was wondering if you helpful chaps could confirm a couple of things for me.

1. I am switching out a slot-in double-oven/ceramic hob electric cooker for a separate 1 1/2 oven and hob. The oven is rated at 5.5KW and the hob at 6.5KW. I currently have a cooker circuit run in 6mm cable and protected by a 40A MCB. The first electrician simply said that I couldn't connect the hob and the oven to the single circuit due to the rating of the appliances. I thought that applying diversity makes this fine and, as the circuit is protected by a suitable MCB, means that the MCB would trip before the cable burst into flames in the case of an overload? I can understand that the ideal solution is a second circuit but this electrician was making out that it had to be done to satisfy the regulations.


2. The first electrician took one look at my consumer unit and said "No RCD protection, you'll need a new one". Is this strictly true? I use an RCD adapter when I plug in my garden tools and the garage has RCD sockets. Alternatively couldn't I fit RCBOs to the two ring main circuits (if I can find any that fit my CU)?


The second electrician basically stated that what the first guy had told me was not true in terms of the regulations. He then quoted me a tenth of the price for the work that I had originally requested (moving a socket so that it isn't behind my new fridgefreezer location and moving the CCU).

Apologies if these seem dumb questions but I am always concerned when two registered tradesmen tell me completely different things.

Thanks in advance.

 

[JohnD]

Are both these electricians members of self-certification schemes? To move a CU and add circuits or new outlets in the kitchen, they need to be (unless you go to the extra trouble and expense of having it inspected and certificated by or for your local authority building control). What recommendations do you have for them?

Your main and supplementary earth bonding may need to be upgraded but this is a fairly straightforward DIY job.

RCBOs may be available, they aren't cheap. They may be considered a superior solution to the use of a split-load CU. What brand and colour is your CU? Do you know what the earthing arrangement is by your meter?
If you can post photos this help.

 

[securespark]

How long is cooker circuit?

40A should be OK unless your circuit is > 32m, assuming no other correction factors.

 

[Demonic]

Both are members of the NICEIC Approved schemes.

I did look into doing the work myself but my LABC office suggested I could get an electrician to do it for less than their charges (£120). I have walls that are made of honeycombed plasterboard (a bit like the cheap doors you can buy) so dropping the cables down the walls is easy enough.

The CU is a Wylex. It's only a six-way and has two ring, two lighting and one cooker and immersion heater circuit. The cooker circuit is (at a guess from the logical route) about 10 metres at most. The house is 15 years old and 32m would go from the CU, round the garden twice and back into the kitchen. I will look to replace this at a later date to give me some additional capacity for some external security lighting and additional sockets in the garage. I just don't want to do it right now as the upstairs is older glued laminate that I don't fancy ripping up just yet.

As for bonding, all I can see at the gas meter is an earth cable that comes down from the CU and is attached to the gas pipe on the house side of the meter.

With regards to the water pipes, there is one large earth cable attached to the main water pipe coming into the house and another linking the two pipes under the kitchen sink. I haven't seen any other such earthing in any of the toikets/bathrooms. Would they need additional bonding if they are all direct feed from the mains water supply? The only thing fed from the cold water tank in the loft is a gravity feed shower (and the hot water/heating system).


As for recommendations, I had none for the first. He was sent round by the kitchen fitters. The second is doing some (subcontracting?) work for a local electrician firm as they have a lot of work on. The main firm came recommended by a colleague who had a full rewire done.

 

[JohnD]

If the Wylex CU is what I think it is, you can't get RCBOs for it. There is a way of RCDing individual circuits from it, but this is not worth the trouble.