Cooker Wiring

[bobscarle]

At the moment we have a gas hob and an electric double oven. We have just bought a replacement oven and a ceramic hob. The existing cable for the oven is 6mm to a cooker switch from the consumer unit with a 30A breaker, 6mm out to connecting point then flex (looks like 2.5mm) to the cooker.

As we are going from gas to electric, I think it needs uprating. This is what I propose to do. Run 10mm from the cooker switch to the consumer unit and change the breaker for 45A. Run 2 x 6mm from the switch, one to the hob the other to the connecting point. Leave the flex to connect to the new oven.

As this is replacement wiring I believe that I can do it myself. Question is, am I correct or would I need to have an electrician make the final connections? Any comments would be appreciated.

Bob

 

[matt]

I'm no expert but my oven and hob each have their own cable run from the CU (6mm I think) and their own CB's. This, I think, was specified by the oven and hob manufacturer, therefore, may not be the norm.

 

[bobscarle]

Matt

According to the instruction guides I can connect both cables to the switch as long as it is rated at 45A. I am hoping that this is the way I can go as I do not have a spare breaker in the CU and adding another is more expense. If you have two 6mm cables, one for the oven and the other for the hob, do you have two switches?

Bob

 

[RogerS]

Bob

Do you have the actual loading of the two units in kW? 10mm is overkill I think you'll find but if you do go down that route then it's not a replacement, I think, and also the kitchen is a special area and so I don't think that officially you can do this yourself BUT I am not an expert.

If it were me I would post the question on askthetrades.co.uk as they are very helpful there.

 

[bobscarle]

Roger

I do not have the loading of the oven but the hob is a little over 6Kw which is around 24A max. As the instructions specify a 45A switch and breaker I thought that it is the upper limit (could even be over) of 6mm cable, therefore 10mm would be better.

I am going to go and have a look on the site you suggested, thanks.

Bob

 

[matt]

Matt

According to the instruction guides I can connect both cables to the switch as long as it is rated at 45A. I am hoping that this is the way I can go as I do not have a spare breaker in the CU and adding another is more expense. If you have two 6mm cables, one for the oven and the other for the hob, do you have two switches?

Bob

Yes, I have two switches.

 

[Digit]

Most built under ovens will run on a 13 amp outlet, but hobs need 30 amp or above, dpending on element size.
You need no sparks to fit a plug and provided you connect colour to colour, live-live, neutral-neutral, earth-earth for the hob you're home and dry!
I would add that heat resistant cable should be used.

Roy.

 

[Oldman]

Bob, your total load if you go to the capacity of the existing switch is around 11kW if the cable run is say 10mtr then you may need 10mm cable.
Use this calc to give yourself an idea.

http://www.tlc-direct.co.uk/Technical/C ... Cable+Size

If the oven comes with a manufacturer fitted 13 amp plug then its ok to use that but if its wired direct to a cooker cable outlet plate then it draws more than 13 amps.
You can buy cooker outlet plates with 2 sets of outgoing terminals enabling you to hard wire both appliances to the same point providing they are within 2mtr.

http://www.alertelectrical.com/Wiring-A ... PRW217.asp

So you can wire both appliances to the same plate.

You only need one switch as long as both appliances are within 2mtrs of the switch and its not mounted behind the hob. The switch is to aid servicing and for use in an emergency when the turkey catches fire.

Unless you can find the data on current draw for the oven and then it and the hob together come under the rating of your present supply cable you are going to need to upgrade to 10mm cable.

Work in the kitchen is a special area and requires an electrician with a part P ticket to sign it off, though if you find a friendly one he may instruct you on how to do the donkey work, inspect and test and issue the paperwork for less money ;-)

 

[Digit]

Most ovens, check, cannot be run at their full rating as various switch interlocks prevent. for example, grill and oven together, which is why they can run on a 13 amp plug.
To check that out it is necessary to establish which functions run at what load. I have yet to see an oven supplied with a lead of any kind and I've installed numerous ones over the years.

Roy.

 

[Oldman]

I have yet to see an oven supplied with a lead of any kind and I've installed numerous ones over the years.

Take a poke around the back of ones in somewhere like Currys Roy, lots of single ovens now come pre wired with 13 amp plugs.
I dare say its a bit less likely with a double oven :wink: which is why I suggested the poster tried to find the data on the oven.

You can usually find a pdf copy of the manufacturers owner manual somewhere on the net.

I have a double oven here that I could run on a 13 amp plug...just.

The top oven is 5.4 amps and the bottom 7 amps, the grill on full is 7.5 amps but as you cant have everything on at once it is going to draw a max of 14.5 amps which a 13 amp plug and BS1362 13 amp fuse will take quite happily though it shouldnt be done as its really not good practice.

Mine didnt come with a lead fitted and requires 4mm cable to a cc plate according to the manual though with 2.5mm twin & earth having a capacity of 24 amps you could quite easily use that without any problems.

 

[Digit]

tried to find the data on the oven.

Absolutely!
If the max WORKING load is less that 13 amp a fused 13 amp supply would be a damned site safer than connection to a 45 amp MCB!
As regards checking at Currys etc, not a chance, if I never see the back side of another cooker it will still be too soon! :lol:
Grease, decaying food, dead mice! I've seen the lot!

Roy.

 

[bobscarle]

Chaps

Thanks for all the responses. It looks like the oven is rated at max 4.8Kw, current draw of around 19 - 20 amps, so well outside a 13A plug. I was expecting this anyway as the existing oven is run on its own supply. The combined current draw for the two appliances would be something over 40A which is a bit much for the poor piece of 6mm.

To my mind I have two options. 1, run a new 6mm cable to feed the hob or 2, run a 10mm cable from the switch to the consumer unit for both feeds. Personally I favour number 2 but I have an electrician popping round on Friday to give his opinion. I am also hoping we can work something out regarding part P.

I like the idea of wiring both appliances from the same plate, that would make it easier if I go down the 10mm route.

Bob (who sometimes wishes he had never started)

 

[RogerS]

You're not going with the advice from Askthetrades then, Bob?

 

[bobscarle]

Roger

Yes, I am going with some of the advice. That said I still think that drawing 40A through 6mm cable is not very good, and that was backed up by another poster. And he did say if was not in a ceiling or floor void then it would not be big enough (35A as against 47A). The suggestion of two 6mm cables came from here and also from askthetrades so there is some support for that and that is one of the two options I have available.

For some reason I still think that the best way to do the job is to uprate the existing cable to 10mm from the consumer unit to the switch and then to the CCU. 6mm and flex to the appliances.

I think that was the gist of the advice given from the two posts. Do you read it differently?

Bob

 

[Oldman]

At the end of the day Bob you will have to install the cable size chosen by your sparky, after all its him who will be signing the job off one way or another.

One consideration if you do go with 10mm cable, the present 6mm could be left in place and used for a radial circuit in the future should you need more 13 amp sockets in the kitchen.

 

[bobscarle]

Oldman

Its very true. Its all down to the sparky and what he wants doing.

Good idea about leaving the 6mm in place.

Bob

 

[RogerS]

Roger

Yes, I am going with some of the advice. That said I still think that drawing 40A through 6mm cable is not very good, and that was backed up by another poster. And he did say if was not in a ceiling or floor void then it would not be big enough (35A as against 47A). The suggestion of two 6mm cables came from here and also from askthetrades so there is some support for that and that is one of the two options I have available.

For some reason I still think that the best way to do the job is to uprate the existing cable to 10mm from the consumer unit to the switch and then to the CCU. 6mm and flex to the appliances.

I think that was the gist of the advice given from the two posts. Do you read it differently?

Bob

I'd need to re-read the thread. Oldman also makes a valid point. One practical thought. Can you get two 6mm cables into whatever you are using to split from the 10mm cable?

 

[davebray]

Hi Bob,
I'm not sure which way you are going to go with this but I can understand why you are thinking of using 2 off 6 mm cables in parallel - they are easier to handle and route through floor joists etc.
But a word of warning - if one of the phase or neutral conductors becomes broken or disconnected then ALL of the load current will flow through the remaining 6 mm conductor with a possibility of overheating of that conductor occurring.
The MCB will not detect an overload current and the RCD will not detect an out of balance current between phase and neutral.
Another point is that when your sparky does his Zs checks for the Electrical Installation certificate you will need (because it's a brand new circuit and in a kitchen) then he will get non-standard R1+R2 readings which could confuse him and he will have to calculate what they should be with 2 off 6 mm cables in parallel rather than look up the 10 mm cable values in the BS7671 tables.
If I have misread your intentions then please ignore this reply.

Cheers
Dave