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
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
Any opinions out there?
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.
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!
Luck is in as Bosch humanoids are on duty today and I picked up a
The actual maximum load for this appliance is 6.49kW; <28 Amps.
Therefore I'll downgrade the MCB to 32A.
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.
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
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..
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