Cooker cable

[Graham.]

My kitchen currently has a dedicated cooker circuit, 6mm cable from a
32A MCB.

New kitchen planned, I now want a new induction hob and a double oven
fitted, the max ratings are 7.2 & 4.2 kW respectively, lets call it a
total of 12kW or 52.17A

AIUI you apply diversity by subtracting 10A then reducing the
remaining figure by 30% that's 22.65A, about a third of the carrying
capacity of 6mm.

The thing is that the electrician is telling me that my 6 mil cable is
not big enough for both appliances, and he wants to run a new cct for
one of them.

Total length of run is about 14m, run in the void under the floor
except the last 4m in a duct through a chase in a concrete floor. I'm
not sure what derating to apply, but surely I've got ample headroom.

The electrician saw the oven I am to use, but to be fair, he had no
idea which hob I had chosen, but I can't imagine any ordinary 4 ring
induction that would break this power budget.

So, sanity check time. Have I got anything wrong? Any advice? (Apart
from the obvious).

--

Graham.
%Profound_observation%

[Michael Chare]

My new 4 ring Bosch induction hob actually has a variable current
limiting feature. The most current it will draw is 20 amps, and you can
have a lower setting. It and a double oven share a cable to a 30 amp fuse.


--
Michael Chare

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[Graham.]

Your hob is 17A max for cable sizing purposes.


--

Graham.
%Profound_observation%

[Michael Chare]

What makes you think that? Apart from anything else the current
limiting feature is a variable. I could set 13 or 16 amps instead.

[Graham.]

On Wed, 28 Jun 2017 00:13:49 +0100, Michael Chare

That's why I said "max", if you set it to 16A or 13A, the diversity
factor has less impact, 14.2 and 12.1A respectivly.

What size cable is it?
--

Graham.
%Profound_observation%

[Bill Wright]

On 27/06/2017 20:49, Graham. wrote:

>

> So, sanity check time. Have I got anything wrong? Any advice? (Apart
> from the obvious).
>

I ran separate cables to separate consumer units (we have three) so that
if there's a trip on one means of cooking she's still got the other.

Bill

[Tim Watts]

On 27/06/17 20:49, Graham. wrote:
>
> My kitchen currently has a dedicated cooker circuit, 6mm cable from a
> 32A MCB.
>
> New kitchen planned, I now want a new induction hob and a double oven
> fitted, the max ratings are 7.2 & 4.2 kW respectively, lets call it a
> total of 12kW or 52.17A
>
> AIUI you apply diversity by subtracting 10A then reducing the
> remaining figure by 30% that's 22.65A, about a third of the carrying
> capacity of 6mm.
>
> The thing is that the electrician is telling me that my 6 mil cable is
> not big enough for both appliances, and he wants to run a new cct for
> one of them.

Have you asked him for his diversity calculation?

[Michael Chare]

I am not certain of the size of the cable but I do know the fuse is 30
amps. But how do you arrive at the 17A?

[Graham.]

AFAIK it's 100% of the first 10A of the total max load plus 30% of tbe remaining load. You can have a single socket too if you allow anorher 5A..

[spuorg...@gowanhill.com]

On Wednesday, 28 June 2017 03:09:15 UTC+1, Bill Wright wrote:
> I ran separate cables to separate consumer units (we have three) so that
> if there's a trip on one means of cooking she's still got the other.

That's so considerate of you, Bill, thinking of her like that.

Owain

[Dave Plowman (News)]

In article <f8bfb292-bcfd-4452...@googlegroups.com>,

True. But wouldn't it be better to arrange things so there never is a
'trip'? A trip is an indication of a fault being present. If it's
something that happened so regularly that you need three independant
feeds, something is very wrong indeed.

--
*The last thing I want to do is hurt you. But it's still on my list.

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[Michael Chare]

On 28/06/2017 09:30, Graham. wrote:
> AFAIK it's 100% of the first 10A of the total max load plus 30% of tbe remaining load. You can have a single socket too if you allow anorher 5A..
>

So how did you get to the number 17?

[John Rumm]

On 28/06/2017 00:52, Graham. wrote:

For hobs with current limiting built in, I would be inclined to take the
limit as the load with diversity already applied and not apply any (or
at least much) further reduction.


--
Cheers,

John.

/=================================================================\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[John Rumm]

On 27/06/2017 20:49, Graham. wrote:
>

> My kitchen currently has a dedicated cooker circuit, 6mm cable from a
> 32A MCB.

So far, so normal ;-)

> New kitchen planned, I now want a new induction hob and a double oven
> fitted, the max ratings are 7.2 & 4.2 kW respectively, lets call it a
> total of 12kW or 52.17A
>
> AIUI you apply diversity by subtracting 10A then reducing the
> remaining figure by 30% that's 22.65A, about a third of the carrying
> capacity of 6mm.

Indeed. Allow an additional 5A if there is a socket fitted to the cooker
point...

> The thing is that the electrician is telling me that my 6 mil cable is
> not big enough for both appliances, and he wants to run a new cct for
> one of them.

For domestic applications, its likely to be fine. Its certainly big
enough in the sense that it won't suffer damage while protected by a 32A
MCB.

The only question that remains is could you get nuisance tripping of the
MCB under full load if you turn on all the hot plates and the ovens at
full chat. The reality is the MCB is unlikely to trip at full load for
going on for a quarter of an hour, and that seems like ample time for
the heating elements to start cycling on their stats.

> Total length of run is about 14m, run in the void under the floor
> except the last 4m in a duct through a chase in a concrete floor. I'm
> not sure what derating to apply, but surely I've got ample headroom.

You could probably count that as installation reference method B, which
gives you a 38A max continuous load capacity.

> The electrician saw the oven I am to use, but to be fair, he had no
> idea which hob I had chosen, but I can't imagine any ordinary 4 ring
> induction that would break this power budget.
>
> So, sanity check time. Have I got anything wrong? Any advice? (Apart
> from the obvious).

I can't fault your logic. So it really comes down to discussion with the
electrician...

Personally I have seen plenty of double oven + 6 - 7kw ish hobs
installed on the single circuit, and don't recall tripping being an issue.

[dennis@home]

On 28/06/2017 12:44, John Rumm wrote:

> Personally I have seen plenty of double oven + 6 - 7kw ish hobs
> installed on the single circuit, and don't recall tripping being an issue.
>
>

I have two single ovens on one feed, they have a maximum of 7.2kW each
stated (I can't see how though as the elements aren't that powerful).

However the 32A breaker has never tripped and I don't imagine running
the three elements in each cooker at the same time for any length of
time unless I am silly enough to put them both into pyrolysis cleaning
at the same time.

The hob is on its own circuit as I think that might be pushing it a bit
too far. 8-)

[tabb...@gmail.com]

reminds me of the entire flat on a 5A rubber feed.


NT

[Dave Plowman (News)]

In article <86af3e76-0188-47c6...@googlegroups.com>,

When I moved in here, there was a 30 amp wire fuse before the CU - which
was much newer than most of the wiring. Lighting was all in lead. A few 13
amp sockets all on a couple of radials. Water heating was an immersion.
Manage like that for a few weeks - including using fan heaters - until a
basic re-wire was finished.
The

--
*The statement above is false

[Michael Chare]

It is quite interesting. If you just have the hob I would be inclined to
agree. However I also have an oven which can draw at least 10 amps. So
in the case of my hob which has rings totalling 30 amps the diversity
rule would count that as 9 amps (30% of 30). But the current limiter is
set to 20 amps. To actually draw 20 amps, 2 rings need to be on max and
a 3rd on partially on.

[Bill Wright]

On 28/06/2017 11:02, Dave Plowman (News) wrote:
> In article <f8bfb292-bcfd-4452...@googlegroups.com>,
> <spuorg...@gowanhill.com> wrote:
>> On Wednesday, 28 June 2017 03:09:15 UTC+1, Bill Wright wrote:
>>> I ran separate cables to separate consumer units (we have three) so
>>> that if there's a trip on one means of cooking she's still got the
>>> other.
>
>> That's so considerate of you, Bill, thinking of her like that.
>
> True. But wouldn't it be better to arrange things so there never is a
> 'trip'? A trip is an indication of a fault being present. If it's
> something that happened so regularly that you need three independant
> feeds, something is very wrong indeed.
>

Very wise words Dave. I won't bother with my car safety belt in future.
I'll simply arrange things so there never is an accident.

Bill

[Bill Wright]

It's just one facet of my general loveliness.

Bill

[John Rumm]

On 28/06/2017 14:27, dennis@home wrote:
> On 28/06/2017 12:44, John Rumm wrote:
>
>> Personally I have seen plenty of double oven + 6 - 7kw ish hobs
>> installed on the single circuit, and don't recall tripping being an
>> issue.
>>
>>
>
> I have two single ovens on one feed, they have a maximum of 7.2kW each
> stated (I can't see how though as the elements aren't that powerful).

7.2kW for a single over sounds fairly high... (many are only around 1800
- 2200W)... you sure its not a kiln you have there ;-)

[Dave Plowman (News)]

In article <oj0hpu$1pqo$1...@gioia.aioe.org>,

You got that one wrong. What it suggests is you regularly have accidents
relying on the seatbelt to protect you from injury.

--
*I know a guy who's addicted to brake fluid. He says he can stop any time.*

[dennis@home]

On 28/06/2017 16:16, Michael Chare wrote:

> It is quite interesting. If you just have the hob I would be inclined to
> agree. However I also have an oven which can draw at least 10 amps. So
> in the case of my hob which has rings totalling 30 amps the diversity
> rule would count that as 9 amps (30% of 30). But the current limiter is
> set to 20 amps. To actually draw 20 amps, 2 rings need to be on max and
> a 3rd on partially on.

Its only 5kW, I think I can manage that with one ring on boost.

[dennis@home]

On 28/06/2017 16:46, John Rumm wrote:
> On 28/06/2017 14:27, dennis@home wrote:
>> On 28/06/2017 12:44, John Rumm wrote:
>>
>>> Personally I have seen plenty of double oven + 6 - 7kw ish hobs
>>> installed on the single circuit, and don't recall tripping being an
>>> issue.
>>>
>>>
>>
>> I have two single ovens on one feed, they have a maximum of 7.2kW each
>> stated (I can't see how though as the elements aren't that powerful).
>
> 7.2kW for a single over sounds fairly high... (many are only around 1800
> - 2200W)... you sure its not a kiln you have there ;-)
>
>

It will get to 500C so its getting close.

[spuorg...@gowanhill.com]

On Wednesday, 28 June 2017 18:25:14 UTC+1, dennis@home wrote:
> It will get to 500C so its getting close.

I bet that makes nice pizza.

Owain

[Bill Wright]

On 28/06/2017 16:46, Dave Plowman (News) wrote:
> In article <oj0hpu$1pqo$1...@gioia.aioe.org>,
> Bill Wright <wrights...@f2s.com> wrote:
>> On 28/06/2017 11:02, Dave Plowman (News) wrote:
>>> In article <f8bfb292-bcfd-4452...@googlegroups.com>,
>>> <spuorg...@gowanhill.com> wrote:
>>>> On Wednesday, 28 June 2017 03:09:15 UTC+1, Bill Wright wrote:
>>>>> I ran separate cables to separate consumer units (we have three) so
>>>>> that if there's a trip on one means of cooking she's still got the
>>>>> other.
>>>
>>>> That's so considerate of you, Bill, thinking of her like that.
>>>
>>> True. But wouldn't it be better to arrange things so there never is a
>>> 'trip'? A trip is an indication of a fault being present. If it's
>>> something that happened so regularly that you need three independant
>>> feeds, something is very wrong indeed.
>>>
>> Very wise words Dave. I won't bother with my car safety belt in future.
>> I'll simply arrange things so there never is an accident.
>
> You got that one wrong. What it suggests is you regularly have accidents
> relying on the seatbelt to protect you from injury.
>

Normally we take precautions against all unfortunate events, even
unlikely ones. In the specific case of the hob and the oven, A short to
ground inside the hob or over would be unpredictable and rare, but it
would be useful if the unaffected appliance continued to work. And if
they are on separate circuits it makes fault finding easier.

Bill

[dennis@home]

It would come out as ash, if it didn't burn the house down.

[Michael Chare]

The large ring on the one I have will do 3.7kw on boast, but if you turn
another ring on the boost goes off!

[Dave Plowman (News)]

In article <5953e678$0$1766$b1db1813$926e...@news.astraweb.com>,

500C on a domestic oven? For what use?

--
*Caution: I drive like you do.

[tabb...@gmail.com]

On Thursday, 29 June 2017 00:01:11 UTC+1, Dave Plowman (News) wrote:
> In article <5953e678$0$1766$b1db1813$926e...@news.astraweb.com>,
> dennis@home <den...@nowhere.invalid> wrote:
> > On 28/06/2017 16:46, John Rumm wrote:

> > > 7.2kW for a single over sounds fairly high... (many are only around
> > > 1800 - 2200W)... you sure its not a kiln you have there ;-)
>
> > It will get to 500C so its getting close.
>
> 500C on a domestic oven? For what use?

AFAIK you can't work clay, glass or metal at 500C. Or food!


NT

[Andy Burns]

Dave Plowman wrote:

> 500C on a domestic oven? For what use?

Self-cleaning ...

[spuorg...@gowanhill.com]

On Wednesday, 28 June 2017 19:56:48 UTC+1, dennis@home wrote:
> >> It will get to 500C so its getting close.
> > I bet that makes nice pizza.

> It would come out as ash, if it didn't burn the house down.

https://www.pizzamaking.com/forum/index.php?topic=268.0

(possibly don't try this if you live in a high-rise)

(on-topic for ukdiy as (a) making your own pizza (b) modifying domestic appliances in an irresponsibly dangerous fashion)

Owain

[Thomas Prufer]

900 °F or 500 °C is about right for a pizza oven...


Thomas Prufer

[dennis@home]

It wouldn't work with these ovens without modifying them.
Its the cleaning cycle and it turns all the grease and sugars to a white
powdery ash you just wipe off.

The mod needed would be to remove the lock on the door as its not
possible to open them once the temp goes above about 250C. It stops
silly people hurting themselves as much.

[Dave Plowman (News)]

In article <erjjga...@mid.individual.net>,

Ah - forgot about that. Just what's needed - fill the kitchen with smoke
and smells. ;-)

--
*I'm not being rude. You're just insignificant

[The Other Mike]

On Tue, 27 Jun 2017 20:49:28 +0100, Graham. <graham...@mail.com> wrote:

>
>My kitchen currently has a dedicated cooker circuit, 6mm cable from a
>32A MCB.
>
>New kitchen planned, I now want a new induction hob and a double oven
>fitted, the max ratings are 7.2 & 4.2 kW respectively, lets call it a
>total of 12kW or 52.17A

I'd be tempted to recheck those ratings for the hob before even considering
diversity.

Our induction hob is theoretically a maximum of 7.2kW on normal
(2*1800W+1*1400W+1*2200W) and 10.5kW on boost (2 x 2500W+1800W+3700W)

With all rings on boost, it would equate to 45A at 230v but there is an overall
current limit you can configure at initial power on in the settings to either
13A, 16A or 20A but no higher, so at 20A its only a total of 4.6kW @ 230v.
--

[Graham.]

Mine has no boost function, and no stated power limits, but it's
interesting that yours has more powerful "burners" when used
individually but it's a less power hungry appliance in total.


--

Graham.
%Profound_observation%

[The Other Mike]

On Tue, 11 Jul 2017 00:48:57 +0100, Graham. <graham...@mail.com> wrote:
>
>Mine has no boost function, and no stated power limits, but it's
>interesting that yours has more powerful "burners" when used
>individually but it's a less power hungry appliance in total.

It's necessary for some Euro markets when they often have an infeed to a
property fused at 16A or 32A rather than the 80A or 100A we have in the UK.

--

[Dave Plowman (News)]

In article <o099mcl7m7968fb9p...@4ax.com>,

The Other Mike <rootpa...@somewhereorother.com> wrote:

In some countries, you pay for the size of the feed as well as leccy used?

--
*All men are idiots, and I married their King.

[dennis@home]

Its more likely to be to make the cooling of the electronics easier.

Its also marketing.
The next hob up from mine can have two rings on boost at a time and has
a higher maximum power output.

[The Other Mike]

On Tue, 11 Jul 2017 13:10:32 +0100, "Dave Plowman (News)" <da...@davenoise.co.uk>
wrote:

>In article <o099mcl7m7968fb9p...@4ax.com>,
> The Other Mike <rootpa...@somewhereorother.com> wrote:
>> On Tue, 11 Jul 2017 00:48:57 +0100, Graham. <graham...@mail.com> wrote:
>> >
>> >Mine has no boost function, and no stated power limits, but it's
>> >interesting that yours has more powerful "burners" when used
>> >individually but it's a less power hungry appliance in total.
>
>> It's necessary for some Euro markets when they often have an infeed to a
>> property fused at 16A or 32A rather than the 80A or 100A we have in the
>> UK.
>
>In some countries, you pay for the size of the feed as well as leccy used?

Yes. but only for the initial connection exactly the same as the UK except by
default they only give a basic supply on a bit of wet string and incrementally
charge for anything better.

Italy has a 3kW more or less universally, but in some old cities you might only
get 1.5kW.

6kW is usually the most you'll get for a one off payment of a few hundred Euros,
10kW and 15kW being options above that for a few thousand Euros.

Up to 25kW is possible on a single phase domestic supply with a huge leadtime,
any more than that and its three phase commercial tarriffs.

To get 25kW as you would with a standard UK domestic supply it can easily cost
1000 euros per kW, often more, with voltage drops right to the very limits quite
normal.

You also pay a different unit charge by supply capability and a different charge
by time of day.

If you can cope with the intermittency and have the space then a 30kWp solar
ground array is cheaper to install as a standalone system. Add a couple of
dozen Tesla powerwalls and its almost like being in England :)
--