Help on kitchen rewire please

maharg · Sep 30, 2009

I have been called to a job by a builder after his electrician walked out.
The client wants a new kitchen installation and after testing the old circuits I have informed him that they are all compromised and need to be replaced.
The current board has no RCD protection and I have informed them that this will need replacement in the future.I do not want to replace the main board yet as based on the kit circuits this would be a can of worms and there is some discusion between builder and client over who is resposible for costs.
In the meantime I have installed a sub-board with a 83A 30ma RCD as main incomer supplied through a Henley block for the kitcen circuits from 100 amp Main fuseI intend to rewire for just the kichen.
Because of the layout of the kitchen and the high spec of the the fitted appliances I have decided to install 2x 4mm radials for the small number of sockets reqired (10).
The hob is 6kw so I am using 6mm with 32A mcb.
The oven circuit has 3 ovens and a built in coffee machine The total wattage of 9850w -43 Amps
I have decided to use 16mm T&E with 50 Amp mcb as max demand on 10 mm is 40Amp.All sockets and ccbs rated accordingly.
I have informed the client that his new board Has allowing for diversity max demand of 85 amps and his old board has 80 amps and told him to contact DNO to confirm the supply setup is satisfactory.
He has also asked me to rewire the lighting circuit.As this would also be connected to the new board increasing the demand .
Firstly.Have I made any serious errors or ommisions
Secondly should I upgrade the RCD to 100Amp 30ma
Thanks for any help or advise

roukel01 · Oct 1, 2009

Hi
Just looking through what the demand is..

The hob is 6kW... checking the old onsite guide, diversity allows the first 10A plus 30% of the remainder which for this gives
6kW is 26Amps. First 10A plus 30% of remainder is 14.8A

The oven. Total load 9.8kW = 42.8 A. First 10A plus 30% of remainder is 19.9A ish call it 20A

So for the largest circuits on your new board Max demand allowing diversity is 35Amps

Will you need more than 2 x 20A radials for the rest of the connected load?? which will bring you way under th 85Amps max demand by the time you've applied diversity to the socket circuits?

Hope I've done this right! Other please ignore me!!

Or am I doing this wrong?

maharg · Oct 2, 2009

Problem is it is not 1 oven @9.8 Kw but 2 ovens at 2.8kw. one microwave/grill oven at 2.950kw plus a coffe machine.
I have used diversity in the following manner:
3 x10 amp=30amp
30% of remainder 5 amp
coffee machine is 6 amp
Total 41 amp
I know the possibility of all 3 ovens and the boiler in the coffe machine all being on full is unlikely but max demand on 10 mm cable is 40 amp.
In addition the client wants 2 lighting circuits with an unknown quantity of wall cabinet toplights 'under counter lights and plinth lights.
Because of the layout of the kitchen which is huge(size of my through lounge) and has laminate floor on concrete,no access to ceiling etc 2 x4mm 20 amp radials are required plus the 15 amp hob circuit.
So without the lights I have calculated max demand
ovens 41amp
hob 15 amp
radials 30 amp
86 amp
Say 15 x100watt luminaires 6.5 ampsx66% = 4.3 amps
a total of 89 amps
.
I have calculated the max demand by using cooker control socket box for the 2 ovens 2x 10 amp +1.3 amps +2x5amp for socket =32 amps.The microwave/grill can be connected by plug.
This reduces my max demand by 9 amps bringing me in at
80 amps but i am not sure if this is just me kidding myself.
Also all my calculations are based on 230 volts but I have noticed that others use 240 volts which also would affect the results by a couple of amps
I would fit a 100 amp 30ma rcd if money were no object but I have to keep costs down and I already have an 83amp.
30 quid here and 30 quid there soon adds up and I got to keep the cost of materials down or i could end up paying for them myself.
Its unbielavable 1.5 million pound house, a new kitchen that without the cost of installation must have cost £25000.00 and because it cant be seen they quibble over the cost of materals.