New Cooker Wiring & Fuse size

[Blenny]

Hi
Firstly let me apologise for asking yet another cooker wiring question, I have looked through previous related posts on this forum trying to find an answer but I just end up being left a bit confused.
I am replacing an old free standing cooker with a new one (double oven & ceramic hob). It would be great if I could use the existing wiring (6mm² x 1.5m lg cable from the wall 45A cooker switch, and I guess 7-8m of the same from the wall switch to the consumer unit which is fitted with a 30A fuse).
The new cooker is rated at 10.4 – 11.3 kW. And the manufacturer (AEG) recommends a 6mm² supply cable, yet my basic (very) understanding of electrics tells me that during a “Christmas day situation” the cooker could be pulling in excess of 45A! So can this be right?
To make matters worse I’ve read conflicting info the web about the required size of cable/fuse, so I’m very confused now can anyone please help?
Many Thanks!

 

[ColJack]

even during a "christmas day" situation the power used by a cooker is never going to be the absolute maximum it's rated for..

the rings and oven all cycle on and off to maintain a temperature..

there is a diversity figure to apply for cooker circuits but I can't remember it off the top of my head..

it's something like 30 percent of the full load plus 15 percent of the remainder and 13amps if there's a socket on the cooker switch..

i'm sure one of the domestic guys will put this right for me..

 

[Adam_151]

Nearly right, most of teh right words, just a tad muddled

Its the first 10A of the cooker load, plus 30% of whatever is left and an extra 5A if there is a S/O on the CCU

 

[ColJack]

if the manufacturer recomends 6mm² then use 6mm²..
however, if in doubt, and to be on the safe side of progress in these cases bigger is usually better.. go for 10mm²

the cost difference isn't that much and in 5-6 years when you buy a bigger and better cooker / oven then a bigger cable may be required.. so it saves you hacking a wall to pieces again..

 

[Blenny]

Thanks for your replies guys!
forgive me but this is where i really show myself up . . .
the cooker wall socket does indeed have a 3 pin socket as well. and doing the maths still gives me a figure (if i've worked it out properly) which exceeds the cable and fuse rating about 38A)!
is this acceptable for the 6mm cable? and how about the fuse?
sorry if i'm being thick but i'd rather be safe than sorry!
thanks again

 

[Blenny]

OOps sorry did the maths and replied too quickly! (i'm supposed to be working)
using your formula i get 26A which sounds OK
(I hope)

 

[JohnD]

You mention a 30A fuse which tells me you have a rather old fusebox.

Ceramic hobs and double ovens do use a of of power, especially at christmas time or other family or friends meals. The Diversity formula might be adequate for typical daily use, but it underestimates the load when a large meal is being cooked.

Stop using the socket on the cooker switch. if you plug in e.g. a kettle or toaster it uses quite a lot of power.

If, when you are doing a lot of cooking, it does blow the fuse, turn everything off; replace the fuse; then turn the ovens on first, once they are up to temperature, turn on the rings one at a time and wait for one to become fully hot before you turn on the next. If you put everything on from cold, it will draw max current and this is when the fuse is most likely to blow.

If you are determined to use a large, all electric cooker (rather than have a gas hob) then before long you need to be thinking about having your old fusebox replaced, and at this time, a new cooker circuit in 10mm cable run, with a 45A MCB. However you cannot have a circuit above 30A from the old fusebox which I think you have got.

If you have an electric shower, or a lot of electric heaters, then using this at the same time as your big cooker might blow the suppliers main fuse

I have nothing against electric ovens, but IMO, electric hobs are a bad idea as they draw so much current. I much prefer gas hobs which are also cheaper to run and faster to respond.

 

[Blenny]

Thanks johnD i here what you're saying
. . . booger!! just when i was feeling a little better about this
yes i do have the old style fuse box and yes a 9kw shower too !
(the shower is on a 10mm cable through a 45a RCB(?) in the fuse box)
What started out as a trip to the shops for a replacement electric cooker (the wife has always used elec. and won't entertain gas ) looks like ending up with with a review of and possible partial rewire of the whole house

 

[JohnD]

can you post a picture of your fusebox?

It it brown, grey or cream?

What text does it have printed, moulded, or stuck next to the main switch?

I bet your wife's mum had an electric cooker. that's what causes women to get stuck in their ways. only solution is to get a replacement wife.

 

[Blenny]

i'll have a look tonight and see if i can get a picture.
on the subject of a new wife . . . wiring the whole house would be easier
it's taken me 28 years to get trained by this one, i couldn't go through all that again

 

[Blenny]

Right . . . fuse boxes are a off white/cream colour and the text by the main switches is "60Watt Max" (oh dear)!
(i took a couple of pictures but am having no luck posting them).
also forgot to mention that i have two of these boxes (side by side)
the second box is left over from when the house had storage heaters fitted,
these where removed when i fitted gas central heating, the box and wired sockets were then changed over to operate as normal "extra" sockets (six 15A fuses).
also looked in metre box to check main fuse but couldn't see a rating.
I think this is heading towards getting "a man in"
cheers

 

[mdbalson]

I have nothing against electric ovens, but IMO, electric hobs are a bad idea as they draw so much current. I much prefer gas hobs which are also cheaper to run and faster to respond.

Only thing with that is that not all houses have a gas supply in the kitchen. I know that in my mum's that there is no gas in the kitchen, so there is an all electric range cooker, on a 10mm cable with a 45amp MCB

 

[JohnD]

//www.diynot.com/forums/viewtopic.php?t=99672

 

[Blenny]

well here are the pictures (sorry about quality)

this is the main fuse board

close up of main board (additional board to the right)

additional fuse board (ex storage heater)

any help?
thanks

 

[JohnD]

neither of them is supposed to take a fuse or MCB above 30Amps.

Each of them is limited to 60A total load

It would be possible to take a 30A cooker circuit off the CU that used to do storage heaters, but it would be better to bite the bullet and move to a new modern CU, and probabaly do some other rewiring at the same time. For example, the shower and sockets ought to be RCD protected. Your meter tails, main earth, bonding and a new isolator will probably need doing as well. can you post a pic of the meter, service head, suppliers fuse and the cables around them? Especially any Green & Yellow earths.

If you do end up having a new CU, I'd suggest getting a good big one, not just a single-way one. Then there will be space to move other circuits to it as time and funds permit. the extra cost of a larger plastic box and some fresh air inside it is not great.

The old ones have probably given 30 years service so it's about time to upgrade.