Installing electric oven & hob

GreeBo · 09-10-2006 2:24pm #1

Hey,
we are replacing our current electric oven and gas hob with an electric double oven and an induction hob.
From what I can see the hob will draw a maximum of 8.2kw (~35 amps)
Im not sure about the oven, will have to check when I get home.

Right now both the (new) oven and the old hob are connected into the same circuit (via a 32amp switch back to a 32amp mcb at the CU)
What is the likely rating for a regular double oven (oven & grill)
Can I just get a 45amp switch and a 45amp mcb or do I need to run a separate 6mm T&E for the hob?
Thanks!

Lex Luthor · 09-10-2006 2:57pm

Greebo, I have a double oven and electric hob in my place running from the same breaker (32A). Hasn't tripped in 10yrs. Chances of you ever having all 4 hob circuits on full and both ovens on full at same time are slim unless you like your cooking or you're cooking for the masses. Regardless, just get out the book for each unit and calculate the expected current draw and work off that.

GreeBo · 09-10-2006 3:04pm

Yeah, but I think the induction hob will push me over the 32amp's pretty often
I will usually have the oven and at least 2 rings on

I think the induction hob is a bigger pull than a regular hob, 8.2 KW's seems pretty high.
Do you know what a regular oven would be, just ballpark?

Also, if "most" oven switches are 45amp, why is it switched down to 32amp at the CU?

dools · 09-10-2006 3:52pm

GreeBo,

Amsure you prob know, but you will need specific pots and pans for an induction hob.

We moved into a second house. They had left all their appliances, one being an induction hob. We could'nt understand why it would'nt work when we tried to cook on it - had no clue about induction. We found out after a week that our pots were not suitable for induction hobs. We had to buy a completely new (v. expensive) set that were compatible. I'd say only about 10% of pots in the shops are compatible

D

GreeBo · 09-10-2006 4:01pm

Yeah, we have ferritic stainless steel pots, designed for induction hobs.
Once your stuff is ferrous it will work..
Thanks anyways!

Idleater · 09-10-2006 4:23pm

I'm no electrician, but when looking for a hob a couple of years ago, the "sales" "staff" said that induction hobs should be on their own dedicated circuit, like an electric shower.

That ruled them out in our house.... Otherwise I think they are supposed to be the closest to gas cooking that electric can get.

L.

GreeBo · 09-10-2006 4:31pm

yeah, Im just not sure if "their own circuit" means the usual cooker one or a totally separate one.
You can just plug a gas hob into the ring main & apparenlty some ovens (single) are the same, < 13amps..
I'll check the ratings on the oven when I get home...

Does anyone know if Im right in assuming that as long as the total max output is < 45 I can just upgrade the switch/isolator and the mcb to 45amp and all will be well?
Is there a minimim size wire I will need for this?
(6mm currently)

Thanks!

Sparky · 09-10-2006 5:03pm

Depends on the oven you have also. Most ovens use feck all and are only fed by a 2.5 flex looped from the hob. Especially if it's inbuilt.

What size is your cooker cable?
It should either be 6sqmm or 10sqmm (thicker than 6sqmm) depending on how far away your main board is.

Either way the 32Amp breaker should be up to the job in an existing installation.
Remember it does have a thermal overload, so it does allow it to go over slightly.
Where it was a new installation with that spec, I would install two seperate circuits.
We have for example a double oven and an induction hob at home, granted not all rings are on full blast at the same time, but the breaker has never tripped.

Its pretty much the same as an instant shower rated at 9kw at full power.
If any human was so step infront of a shower on full they would be scalded. So generally 9kw of juice is never used.

40amps is the next size up and is not recommended by the ECTI rules.
The breaker is there to protect the cables remember.

Lex Luthor · 09-10-2006 5:38pm

stupid question...whats an induction hob?

GreeBo · 09-10-2006 6:14pm

Sparky-s wrote:

Depends on the oven you have also. Most ovens use feck all and are only fed by a 2.5 flex looped from the hob. Especially if it's inbuilt.

What size is your cooker cable?
It should either be 6sqmm or 10sqmm (thicker than 6sqmm) depending on how far away your main board is.

Either way the 32Amp breaker should be up to the job in an existing installation.
Remember it does have a thermal overload, so it does allow it to go over slightly.
Where it was a new installation with that spec, I would install two seperate circuits.
We have for example a double oven and an induction hob at home, granted not all rings are on full blast at the same time, but the breaker has never tripped.

Its pretty much the same as an instant shower rated at 9kw at full power.
If any human was so step infront of a shower on full they would be scalded. So generally 9kw of juice is never used.

40amps is the next size up and is not recommended by the ECTI rules.
The breaker is there to protect the cables remember.

Right now the cable is 6mm
The oven is rated as 5.5kw
The hob is rated as 7.2kw
so by my calcs thats about 23 +32 = 55amps

I guess thats also with everything on full power (self cleaning oven, all the rings on full)
So that says to me that I really need two 6mm cables on two 32amp mcbs
Am I correct?
Thanks for your help...

Lex, an induction hob is one that uses a moving magnetic field to generate heat.
The heat is generated in the pan, not the hob so there is less energy wasted (about 85% efficient versus 40 odd)

Copper · 09-10-2006 8:39pm

Your wiring should be fine as it is.

You should take diversity into account when considering the design current for the cooker circuit. You should never have cause to have your cooker and hob wide open i.e everything on full power at the same time, unless you're cooking for an army!

For an oven, diversity is normally taken as 10A plus 30% of the remainder of the max demand current (I.E.E Regs) For 13 kW this is around 25 Amps, i.e you should design your circuit around a load of 25A.

This means design current Ib = 25A.
MCB rated current In = 32A.
Current carrying capacity of cable Iz > 32A
Cable size should therefore be 6 square or greater.

Having said that, if it was a new installation I would be happier running two separate 6 squares to avoid nuisance tripping if you happen to exceed 32A in times of high demand (around Christmas for example).

I'd imagine you would usually find yourself drawing no more than 20A (20A is a huge current in a house).

Although the cooker and hob have a theoretical max demand of 55A, they will never be able to draw near this, even if you were to turn everything on.

The hob and cooker can share the same isolator so long as they are within 2m of each other, if further apart than this they need separate circuits and isolators.

GreeBo · 10-10-2006 10:15am

Great, thanks for that copper.
Can you point me in the direction of those I.E.E regs (if they are online) Id like to have a read.

Also, when I was buying a replacement isolator switch they (B&Q

) had 32amp and 45amp.
When would you use 45amp?
does it depend on the gauge of wire between the switch and the units?
(the hob is <2m from the oven btw)

Copper · 10-10-2006 8:38pm

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

http://www.borpin.co.uk/sbfaq/faq51182.htm

You should use a 45A cooker switch and not a 32A double pole switch. As far as I know the cooker switch would be built to a specific BS standard relating to cooker control units wheras the double pole switch would not.

Also, if "most" oven switches are 45amp, why is it switched down to 32amp at the CU?

I think they just manufacture a standard 45A switch, assuming 10kW to be a standard oven.

GreeBo · 16-10-2006 1:33pm

Copper wrote:

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

http://www.borpin.co.uk/sbfaq/faq51182.htm

You should use a 45A cooker switch and not a 32A double pole switch. As far as I know the cooker switch would be built to a specific BS standard relating to cooker control units wheras the double pole switch would not.

I think they just manufacture a standard 45A switch, assuming 10kW to be a standard oven.

Hey, thanks for your replies.
Do you know what the difference between the two types of switch is?
The only "modern looking" 45 amp cooker switch I can find is a double socket size, but I really want to use a single sized one (which is 32amp)
Wont the MCB trip before the switch takes anything higher than 32amp?
Thanks again!

Sparky · 18-10-2006 9:52am

The switch is only rated to take the current before it starts to breakdown. If your MCB is 32amp rated it would trip if current reached it.

When you say modern, what do you mean?
Here is some single gang 45amp DP switches.
http://www.meteorelectrical.com/catalog/590

Installing electric oven & hob

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