Electric oven and hob wiring

[Reg_Prescott]

Hi all.

I'm after some advice. My existing fan assisted electric oven is supplied by the kitchen ring main via a 13A fused spur (I don't know what the existing oven is rated in terms of kW). The electric hob is on its own cct with a control unit and 32A MCB. All cables to the hob are 6mm^2. The power rating of the hob is 6.2kW.

I was suprised that the oven was on the ring main, but I have since read that this is OK provide the oven is less than 3kW. Is this correct?

Anyway, here's the thing. The oven is crap. It takes ages to heat up and is generally falling to bits. So a friend has given me an oven (Hotpoint BU62 if it helps)

The new oven is a double oven rated at 5.2kW. Is there any way I can have the hob and oven the same cct, with the existing wiring?

My trusty DIY book (1994!) suggests a 32A MCB and 6mm^2 wiring is good for "cookers" up to 16kW.

How is this worked out?
I'm thinking (new oven) 5.2kW + (old hob) 6.2kW = 11.4kW

11.4kW/240V=47.5A This say to me It can't... what am I missing?

Any advice on how I can make use of my 'new oven' would be much appreciated. Or would I be better off buying a replacement single oven that can run from a 13A supply and leave everthing as it is? What would you do?

PS I am skint

Thanks in advance,

Mark

 

[Steve]

Your DIY book is still correct. It takes into account something called diversity, which takes an "average" of the load. While generally it isn't applied to fixed loads, its allowed on a cooker because there are many heaters cycling on thermostats, so full load will very rarely be drawn. You cant do this on a shower because full load is drawn all the time.

Most cookers in this country are wired from a 32A MCB and 6mm² cable, and rarely have problems. A 32A MCB will take more than this for a certain amount of time. Nothing will catch fire if you do overload it - the 6mm² cable and the accessories are protected by the MCB.

 

[securespark]

11,400W total load.

Apply diversity:

11,400W=49.57A

Take first 10A = 10A

Plus 30% of remainder=11.87A

Plus 5A if have s/o on plate

26.87A

 

[Reg_Prescott]

Thanks guys,

That is exactly the sort of answer I was looking for. I have a couple of further questions I hope you can answer.

I have just discovered that there is a double socket taken off the control unit as a spur. It is positioned right next to the control unit.

1.) Is this OK? I have seen sockets built into the control unit before, but not a double socket like this.

2.) If a double soket is allowed, does it affect the diversity calculation?

3.) Assuming the above is OK, another quick question regarding the wiring:

The existing 6mm^2 cable is only long enough to reach the hob.

Assuming the terminals on the hob are large enough to accept two 6mm^2 cables, is there any reason why I can't connect the oven there? (The oven is directly under the hob)

Thanks again,

Mark

 

[stem]

1) No this is wrong. The only allowance on a cooker circuit is the one socket integral with the control unit.

2) as 1 above.

3) That's fine if the terminals are big enough.

 

[Reg_Prescott]

Thanks Stem

The double socket didn't seem right to me. Apart from anything else, it is not obvious (I discovered it beacuse I couldn't make a cup of tea after I had switched the kitchen ring back on - I had left the hob isolated)

I hope the terminals are large enough at at the hob - as that makes for an easy job.

Thanks for the swift response!