replacing all-in-one cooker with separate hob & double o

[ekon]

At the moment we have an all-in-one cooker with max. wattage rated at 10085 W. (44 amps at 230V). The cooker switch "box" has a separate plug-socket on it but I rarely use that socket. The cooker itself is fed from its switch-box by about 1m. of what appears to be 6mm2 T&E (externally about 15mm broad) into a 30A junction box from which another 1m of what appears to be 4mm (about 12mm broad) goes to the cooker.

The whole thing is on a separate 32A mcb-protected radial circuit from a Legrand main-box that was professionally installed 9 years ago. We have never had a moments trouble with this installation or the electrics in general.

The kitchen is being revamped. I have bought for a very low price (from a good friend) a double-oven (Neff 1422) which is fairly new..2-3 years...hardly used. It is rated at 4.6kw and has a tail of what looks like 4mm2 T&E which has just been cut 10" from the oven back when it was removed from its original setting (not by me).

The hob we want to buy is rated at 6400W. so overall the max. loading is 915 W. more than before...i.e. 11000W (48A @230v)

Given the existing cooker installation has never caused us a problem and we're only adding less than a KW) would it be ok in principle to create a "star" on the end of the circuit..taking 2 lengths of 4mm2 from the existing 32A junction box..one to feed the new oven the other to feed the adjacent hob? The existing cooker switch-box would probably be replaced with one without an ancillary socket. There would be very few, if any, occasions where max.load would be approached as there are only two of us in the house..on the existing cooker we rarely use both ovens at once for example.

The alternative would be to run a new (separate for the oven alone) radial circuit from the main-box 10 m away (across the loft-space and down into the kitchen..its a bungalow). I do have one spare 32A mcb at the moment.

Guess this is PartP work and really I should get an electrician in? Well I would anyway tbh if I went for the separate radial circuit..I don't want to be messing with the main-box.

Thanks for reading what I know is a long post but I wanted to try and include all relevant details at the outset (I expect I've still left something vital out!). Any comments gratefully received.

 

[ban-all-sheds]

At the moment we have an all-in-one cooker with max. wattage rated at 10085 W. (44 amps at 230V).
.
.
The hob we want to buy is rated at 6400W. so overall the max. loading is 915 W. more than before...i.e. 11000W (48A @230v)

It's actually 20A and 21A.

http://www.tlc-direct.co.uk/Book/6.2.1.htm

Given the existing cooker installation has never caused us a problem and we're only adding less than a KW) would it be ok in principle to create a "star" on the end of the circuit..taking 2 lengths of 4mm2 from the existing 32A junction box..one to feed the new oven the other to feed the adjacent hob?

1) You'll find it much easier to get 2 cables in if you replace the cooker outlet plate with a dual one:



2) It would be better to use the same size cable throughout, if it will fit into the appliances - what do the makers' instructions say?

 

[ekon]

thanks b-a-l..yes I see! That's why we've had no problems with the 10.08KW cooker on a 32A mcb!!

Thanks for the advice on the part too..I think I'll get one and go that way rather than getting a spark in to run a brand new radial circuit from the main-box. Can't see the extra potential max. load of 915w should upset the system.

I think 4mm would be ample from the dual cooker outlet plate..but I may have some perfectly good (old) 6mm2 kicking around. From your photo looks like I'd get 2 lots of 6mm in on the outlet side? Maybe the new oven or hob wouldn't (physically) take it..but if so that'd also be ok wouldn't it?

 

[Taylortwocities]

You should be fine with that load.

When assessing the load for cookers we use what is called diversity. Basically it works on the basis that with a ccoker (or hob) you'll never have a time when all the rings and/or both ovens will be on and being energised all at the same time.
Each ring and oven has separate thermostats and these are constantly clicking on and off so the actual running load is almost always less than the total theorectical total.

Here's a good example.
Lets suppose the main fuse from the lekky board into your house is rated at 100amps.
Go count up the total values of all the MCBs in your consumer unit. It will be way more than 100amps.

Also, can you imagine what would happen if the lekky board sized their network for 100amps for every house? You'd need many, many more
additional power stations.



You'll be fine, even on Christmas Day.

 

[ekon]

thanks ttc..yes I had heard about "diversity" in an electrical context....thought it meant sparkies had to be ultra pc !

p.s. gonna bash on with the job myself..one little last Q...anyone know if you can pull the mcbs out of a Legrand "main box"? (before working..belt & braces etc!)..before I try it & it's not designed to be pulled at!!

 

[Taylortwocities]

p.s. gonna bash on with the job myself..one little last Q...anyone know if you can pull the mcbs out of a Legrand "main box"? (before working..belt & braces etc!)..before I try it & it's not designed to be pulled at!!

You would have to unscrew it from the busbar. You would be far safer just turning off the MAIN SWITCH on the consumer unit. Leave the MCBs alone.

 

[ekon]

thanks again ttc..think there's at least one brand of consumer unit where the mcbs slip out (Wilex?)..anyway as I said it was just the braces (of the belt& braces)..MAIN SWITCH as you say...I'll also switch power off at the meter box..have a healthy fear of leccy after I got a fair "tingle" in Cyprus when we were living there...I had switched off the main switch on the consumer unit and something still nibbled me when putting up a PIR security lamp outside!

Ordered one of those 2 way outlet plates..from the same place as b-a-s got the piccy..reading the reviews one guy said "Does make oven and hob easier to install but beware, a fuse is usually still needed before the start of the oven cable." Is that right?..I'll do anything sensible if it adds to safety..what would he be referring to though? & what fuse rating? given its 4.6kw (with "diversity") 18.33 amps (10 + one third of 10 + 5..is that right?)

 

[ban-all-sheds]

He's probably referring to a small oven which needs a 13A circuit.

What do Neff say your oven needs?

BTW - your nibble in Cyprus happened because you didn't do things properly and check for dead.

 

[ekon]

Yes very true..lesson learned I hope..mea culpa.

No manual with oven (..must hunt one down on the net). .but there is another thread on here I found where the author says "The (same) oven isn't supplied with a connection cable and the manual tells me I need a cable H05RR-F 3 G 1.5"

I think this is heat resistant 1.5mm2 cable..there is an interesting thread on another forum too:
http://www.diybanter.com/uk-diy/185183-cooker-flex-cable-again-2.html

hope its not against the rules to post a rival(?) forum.

I shall go with 6mm2 if it'll go in the back of the oven...if physically impossible I shall stick to the 4mm2 that has obviously been supplying it before.