MCB Rating for new hob

[Vortex]

Hi,

We're in the process of installing a new kitchen and have purchased a new Bosch ceramic hob for it.

I fell of my seat when I read the specs:

8.29 kW total load........36 Amps. (Bosch 865E)

Bearing this in mind I installed a 6mm dedicated cable, fed from a 45A dedicated MCB.

Yesterday I opened the box and see that with the installation manual Bosch recommends minimum 25A capable supply.

Clearly there is conflicting information and I'm wondering if a 45A MCB is somewhat excessive. To be honest its hard to even imagine a practical circumstance where every ring of a hob will be on "full wack" from a simultaneous cold start.

I suspect it will be a few days before I can talk with a humanoid in Bosch support...in the meantime I am wondering if I should "downgrade" the MCB to

32A.

Any opinions out there?

David

[Huge]

^^^^^^^

[17 lines snipped]

Send it back. Ceramic hobs are cack.

[Matt Beard]

2 points:

1) Electric hobs all work by the same basic principle, they control their temperature by modulation - i.e. they turn full on, then full off and the ratio between the two varies to change the temperature. With all four rings on, no matter what level they are set at, there will be times when all are on full. Result - you will trip a 32A MCB.

2) Check your cable calculations - Chances are you are going to be able to melt that 6mm cable without tripping a 45A MCB!

[ANt]

36A is assuming full load (8290W / 230V = 36A)

From other posts it sounds like one takes the first 10 Amps of the total and 30% of the remainder to come to a realistic load based on the fact that you won't have everything drawing its full current at the same time so that would give you 10 + (26 * 0.3) = 17.8A. So a 25A circuit sounds suitable.

Personally, I'm having a double oven (2.5kW + 1.85kW = 4.35kW) with a ceramic hob (7.7kw total) fitted. Total is a little over 12kW ..roughly 53Amps. So I'd need a minimum 10 + (43 *.3) = 23Amp Circuit using the 10A + 30% rule.

From the CU to where the oven/hob will be is about 15 metres and I plan to run 10mm^2 from a new 40A MCB giving a fair bit of capacity over the minimum 23Amps. Once the cables under the floor, it's over to the fitter to do the rest (I need to lay the cable first as he won't have access under the boards in the adjoining room by the time I've cleared the kichen out!) The cable size is a little overkill but when it comes to upgrading the circuit in the event of the next owner wanting a larger oven/hob it'll be less intrusive to put a new CU and larger MCB in than replace the cabling that'll be embedded behind the plaster.

I would have liked to put a larger MCB in but the CU is a fairly old Wylex plug in MCB type and I haven't found anything larger than 40A that's likely to fit - I haven't actually checked the CU capacity yet so I may have to change the whole thing anyway. In fact I'm waiting for the delivery from tlc before I can be sure that the newer style MCBs will fit.. Ant.

[ARWadsworth]

Use a 40A MCB.

-- Adam

adamwadsworth@(REMOVETHIS)blueyonder.co.uk

[Vortex]

Luck is in as Bosch humanoids are on duty today and I picked up a documentation error.

The actual maximum load for this appliance is 6.49kW;

[Vortex]

Thanks for the constructive and helpful advice.

[Christian McArdle]

Not true. You would need to draw 96A to have a chance of instantaneously tripping a 32A MCB (160A to guarantee tripping it). There is much diversity to be had from hobs. It is the average over many minutes that determines what MCB is required. In practice, an overload of only 4A may never trip a

32A MCB at all, no matter how long it happens.

Christian.

[Graham Nye]

[Huge wrote:]

It's accurate, if somewhat brief. Gas hobs are much more controllable, if you have the option for a gas supply. You need a special cleaning solution to remove any baked-on deposits as you need to avoid scratching the hob surface.

My wife used to have a ceramic hob. We now have a gas hob and no plans to change back.