Hard Wiring an electric cooker

[nattye84]

I have just bought an electric cooker which appears to have no plug. I already have an isolation switch in my kitchen. The appliance has a power output of 10.0kw and says that it must be hard wired to a separate 45amp cooker circuit. Does anyone know how to do this?

[ianmunt]

the isolation switch should have a direct connection to your consumer awith at least a 45amp fuse/overload trip.
If this is so you need 6mm twin+earth cable to connect between cooker and isolation switch.The SUPPLY TO THE ISOLATION SWITCH must be off throughout the connection procedure..This is heavy stiff cable that is not very easy to handle,and needs to be very firmly clamped at each connection terminal.
However,having said all that,DIY kitchen (and bathroom) wiring is not permitted under current regulations and you should only have the work carried out by a qualified tradesperson

[ianmunt]

the isolation switch should have a direct connection to your consumer unit with at least a 45amp fuse/overload trip.
If this is so you need 6mm twin+earth cable to connect between cooker and isolation switch.The SUPPLY TO THE ISOLATION SWITCH must be off throughout the connection procedure..This is heavy stiff cable that is not very easy to handle,and needs to be very firmly clamped at each connection terminal.
However,having said all that,DIY kitchen (and bathroom) wiring is not permitted under current regulations and you should only have the work carried out by a qualified tradesperson

[tezestwing]

nattye84 Ian is spot on but he has not mentioned the all important connection unit that should go between the appliance and the isolation switch unit per regs this saves any need to go into the isolation switch and makes for a easy connection see here http://www.screwfix.com/search.do;jsessionid=I EUIG5IFMUMZMCSTHZOCFEY?_dyncharset=UTF-8&fh_se arch=cooker+connection+unit If you dont have this then you need to get a sparky in to fit one HTH Tez

[ianmunt]

I rather assumed the "isolation"switch was a cooker connection point

[matt1e]

"the isolation switch should have a direct connection to your consumer with at least a 45amp fuse/overload trip."
NOT SO
6mm at he very most can carry 47A this is ONLY when clipped direct on its own from consumer unit to appliance
when enclosed in a insulated wall this drops to 35A in trunking/conduit drops to 32A
10mm gives 64A/47A and 44A respectively so as you can see there is only one instance for 6mm and two for 10mm where it is permissible to use a 45A breaker

There are many factors to be considered when choosing the size of cabling and overload protection
ie
circuit load
type of cable
method of installation
method of overload protection
cable length
external fault loop impedance
etc
and on top of that you have to apply correction factors to allow for grouping/diversity etc
for example a 6 mm Twin and cpc enclosed in conduit in a thermally insulating wall =32A
10mm Twin and cpc enclosed in conduit in a thermally insulating wall =44A
However this is probably above the actual rating you will need for a cooker as diversity is applicable

[matt1e]

To apply diversity as per On site guide
Add up all the loads on the cooker and calculate the current required at 230 volts
for example a cooker with 10kW worth of load would work out at 44 Amps
Take the first 10 Amps plus 30% of the remaining load
So 10 + (34 x 30%) = 10 + 10.2 = 20.2 Amps
If a 13A socket is present on the cooker switch add another 5 Amps

So you are looking at either a 20.2 A design current or a 25.2 A design current depending on the presence or not of a 13A socket
If you do have a socket the disconnection time will be 0.4 seconds in the event of an earth fault or 5 seconds (16th edition) without a socket.
For a type B circuit breaker both conditions are fulfilled anyway but a fuse will behave differently.

6mm will have a volt drop of 7.3mV per A per metre so with say 10 metres of 6mm cable at 25.2A you will drop 1.9 volts (less with 10mm at 4.4mV/A/m) Which is well within the 4% permitted volt drop of 16th edition iee regs and certainly within the increased 5% drop for power circuits of the 17th

so if your existing cable is a 6mm it should be ok if protected by a 32A type B circuit breaker and again I will say
DO NOT protect this cable with a 45A mcb/fuse if the existing cable is 10mm then a 45A mcb will most likely be ok but probably not needed
also it has been mentioned about the tightness of connections this is very true and most important but nothing has been mentioned regarding the cpc (earth wire)
In a twin and earth cable the cpc is never sleeved this DOES NOT mean it doesn't have to have one it MUST be sleeved at its terminations with appropriate green/yellow sleeving

[ianmunt]

In simple terms,do not DIY get an electrician in !

[matt1e]

just in case i've confused you natty as far as the final connection is concerned (cooker outlet to cooker) Ianmunt is quite correct you will need no bigger than a 6mm cable even if tho outlet is fed in 10mm this is because the 2 metres or so of cable required to make the connection will be in open space and treated as clipped direct and therefore capable of carrying 47A

[tezestwing]

the whole point is natty you need to identify the size of the existing cable so if you are not able do that then leave it for the experts however if you have a 45 amp mcb fused protection already for the circuit it MAY be 10 mm but as matt suggests have it checked for peace of mind HTH tez