by ericmark »
Tue Sep 06, 2011 7:11 am
There is nothing to say a kitchen should have a dedicated final ring or any sub-main however it does say:-
RING FINAL CIRCUIT ARRANGEMENTS, REGULATION 433.1.5
The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:
(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile from the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit
If one was to take this rule by the letter the whole idea of having a bank of switches marked tumble drier, washing machine, etc. coming from a dedicated kitchen ring would be out and each switch should have it's own radial circuit in the same way as a cooker does.
In practice the running of washing machine, tumble drier, from the ring is still done even if it does not strictly comply.
However there is one problem which haunts many of an electrician and that is anything new must comply with latest regulations so when adding sockets to a non RCD protected circuit one has to include RCD protection. One socket is easy just use Ali-tube cable and a RCD socket or run the cable surface and use a RCD socket. Problem being that unless the special Ali-Tube to BS 8436 Guardian, Earthshield, or Flexishield, Afumex, according to manufacturer rated 90 deg C is used then either the cable has to be RCD protected or run through metal conduit if buried in the wall. So using trunking means they don't have to use Ali-tube.
The problem with Ali-tube is it's not only slightly more expensive but often can only be bought by the role. Unlike twin and earth where one can buy 5 meters from B&Q one often has to buy 100 meters. In theory for an electrician this should be no problem as he will in the end use it. But most jobs using any length of cable will have RCD protection so he would have it on his hands for a long time and as I said it's expensive.
So in the main electricians try not to buy a role and use surface wiring where to bury cable would require use of Ali-tube.
It is not only the electrician but also the client as of course it is far cheaper to surface mount cable. And with a kitchen often with a little thought cables can be hidden with the units fitted.
The regulations are designed for all and so do not say you must fit a dedicated radial or ring but say it in a more roundabout way so where used in special situations one has multiple ways to comply.
It is very easy to make an error when commenting on something like this. A washing machine, and tumble drier are not kitchen appliances (even though often are in a kitchen) and the dishwasher is not used in all kitchens so with dedicated supplies for hob and oven one could very well have nothing exceeding 2kW and also have RCD protection on all circuits which would likely mean the only loads onto the ring are from portable appliances like the kettle. In which case no need for new supply for kitchen.
However if going by the letter and you need dedicated supplies for washing machine, tumble drier, and dishwasher, (All normally over 2kW) then running three extra radials back to the consumer unit will likely present problems maybe even require a new consumer unit. One way used to get around the problem is to run SWA cable around outside of house to the incoming supply and have a mini consumer unit in the kitchen. There are some advantages with this in that also it doubles as local isolator so no need to fit grid switches to isolate the washing machine. (If you have ever seen one when the weights come lose you would never consider fitting one under counter without local isolator).
However under the Part P regulations the electrician if part of a scheme has to sign for design, installation and testing you are not permitted to undertake one of the three functions. To have separate signatories one would need to register the work with LABC which again would cost. So to get any other system installed you have to persuade the electrician that he should change his design. One would hope he is flexible and open to suggestions but he is signing the paperwork so it's his call.
I will guess RCD protection is the problem but you don't say if circuits are RCD protected or not.
