Re: Electric Oven advice ?

[newshound]

On 26/02/2022 16:38, Jethro_uk wrote:
> Looking at a Hoover HO7DC3B308IN
>
> Hoovers website doesn't appear to have heard of it.
>
> Currys and Hughes (2 main stockists) don't seem to have a clue either
> (although to be fair to Hughes they did open a manual in store for me and
> we confirmed there is no specs about power supply).
>
> I'm guessing from the fact that it doesn't come with any cable means it
> needs to be wired into a dedicated circuit ? Which our kitchen has the
> remnants of from the CU. Just no feed from the wall.
>
> My impression is regs need the oven to be wired in directly - no plug ?
>
> What sort of cabling is appropriate ? 4mm, 6mm ?

It's a built-in double oven. It will be hard-wired to an isolating switch.

[charles]

In article <svdmfp$4e2$2...@dont-email.me>,
Jethro_uk <jeth...@hotmailbin.com> wrote:

> Which was fitted when we moved in. However since we were gas, I blanked
> it. So that's the feed from the CU sorted.

> However what spec cable is needed to go from there, through the conduit
> below and thence to the oven ? Which is going to need a junction box
> fitted to the wall behind the cooker and the cooker connected to that ?

> not sure 6mm will go into the conduit, but 4mm will.

if you use 6mm singles, not T&E, it probably will.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

[Theo]

Jethro_uk <jeth...@hotmailbin.com> wrote:
> Looking at a Hoover HO7DC3B308IN
>
> Hoovers website doesn't appear to have heard of it.
>
> Currys and Hughes (2 main stockists) don't seem to have a clue either
> (although to be fair to Hughes they did open a manual in store for me and
> we confirmed there is no specs about power supply).

Currys say it's 5.09kW:
https://www.currys.co.uk/products/hoover-hoven-300-ho7dc3e3078in-electric-builtunder-double-oven-stainless-steel-10207020.html
(is that the same model?)

3kW per oven sounds about right, so let's go with that.

For diversity, the rule is 10A plus 30% of the remaining load, plus 5A for
an additional socket on the cooker point (irrelevant here).

If it's 6kW that's 26A. So rated current needed 10+(16*0.3) = 14.8A.
If it's 5.1kW that's 22A, need rated current = 13.6A

According to TLC's calculator:
https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
a 1m T&E cable clipped direct carrying 6kW should be 2.5mm2 at 30C and 4mm2
at 40C or 50C. 5.09kW at 40C needs 2.5mm2.

Given it's a cooker I'd plump for the high temperature and go with 4mm2.

> I'm guessing from the fact that it doesn't come with any cable means it
> needs to be wired into a dedicated circuit ? Which our kitchen has the
> remnants of from the CU. Just no feed from the wall.
>
> My impression is regs need the oven to be wired in directly - no plug ?

You might be able to run it off a plug at 13.6A and get away with it
(especially if both ovens aren't run at once), but I wouldn't - it's better
to be hardwired (and I think regs would expect that).

It might work via a non BS1363 plug - 16A caravan connector or something -
but I can't see why to do that unless there's a good reason (disconnecting
for maintenance?)

Theo

[Roger Mills]

I would expect it to need a dedicated radial circuit in (probably) 6mm
cable, connected to a 32A MCB and with an accessible isolator switch
near the oven.

It sounds as if you've already got most of this. Is there a flush or
surface mounted cooker control unit with a big red switch (and possibly
a 13A outlet as well) with wiring going down to a cooker outlet
connection? If so, just connect the oven to this outlet.
--
Cheers,
Roger

[ARW]

On 26/02/2022 17:40, Theo wrote:
> Jethro_uk <jeth...@hotmailbin.com> wrote:
>> Looking at a Hoover HO7DC3B308IN
>>
>> Hoovers website doesn't appear to have heard of it.
>>
>> Currys and Hughes (2 main stockists) don't seem to have a clue either
>> (although to be fair to Hughes they did open a manual in store for me and
>> we confirmed there is no specs about power supply).
>
> Currys say it's 5.09kW:
> https://www.currys.co.uk/products/hoover-hoven-300-ho7dc3e3078in-electric-builtunder-double-oven-stainless-steel-10207020.html
> (is that the same model?)
>
> 3kW per oven sounds about right, so let's go with that.
>
> For diversity, the rule is 10A plus 30% of the remaining load, plus 5A for
> an additional socket on the cooker point (irrelevant here).

I disagree. That diversity is for a cooker that comprises a hob with 4
hot plates and one or two ovens - in this case you just have two ovens
and you cannot apply that sort of diversity.

> If it's 6kW that's 26A. So rated current needed 10+(16*0.3) = 14.8A.
> If it's 5.1kW that's 22A, need rated current = 13.6A

So rate the cable for 26A.

If using H07RNF flex then that is 2.5mm.

--

Adam

[ARW]

Why does the switch need to be red.

From the Curry's site

"ELECTRICAL INSTALLATION: This product requires professional
installation to a dedicated cooker circuit (identified by a big red
cooker switch) by a qualified installer, such as one of our Currys experts."

A Scolmore CMA504 is not red

[Animal]

... If the cable is in a cold situation. If it gets hot where it runs inside the oven it'll have less ampacity & need derating & thus 4mm cable. So it depends on the oven design.

[John Rumm]

On 26/02/2022 16:38, Jethro_uk wrote:
> Looking at a Hoover HO7DC3B308IN
>
> Hoovers website doesn't appear to have heard of it.
>
> Currys and Hughes (2 main stockists) don't seem to have a clue either
> (although to be fair to Hughes they did open a manual in store for me and
> we confirmed there is no specs about power supply).

B&Qs web site helpfully suggests the power output is 13W :-)

(might be true if you only have the light on!)

> I'm guessing from the fact that it doesn't come with any cable means it
> needs to be wired into a dedicated circuit ? Which our kitchen has the
> remnants of from the CU. Just no feed from the wall.
>
> My impression is regs need the oven to be wired in directly - no plug ?

Yup - it does depend on the actual capacity. A double oven is very
unlikely to be over 7kW, so a 32A protected radial will likely be more
than adequate.

> What sort of cabling is appropriate ? 4mm, 6mm ?

Normal T&E as far as the isolator, and ideally a length of high temp
flex for the final connection. Something like 2.5mm^2 H07RNF should be
ok for the final connection. The T&E size being dictated by the length
of the circuit and the any other de-rating factors encountered along the
way.

Chapter and verse here:

http://wiki.diyfaq.org.uk/index.php/Calculating_A_Cable_Size

(note that a typical "cooker" circuit wired in 4 or 6mm^2 cable will be
more than adequate, since that will be specced to supply an over and hob
combo, and it is usually the hob with the larger peak current draw)

--
Cheers,

John.

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

[Fredxx]

In which case the instructions should say; if the connections are
subject to heat from the oven itself. Otherwise I don't why it should be
treated differently to any other appliance?

[Animal]

the difference is only that heat reduces ampacity, hence some ovens/hobs that would appear to be fine on 2.5 require 4mm - and some don't.

[Mike Clarke]

On 26/02/2022 18:23, ARW wrote:
> On 26/02/2022 17:40, Theo wrote:

[snip]

>> For diversity, the rule is 10A plus 30% of the remaining load, plus 5A
>> for
>> an additional socket on the cooker point (irrelevant here).
>
> I disagree. That diversity is for a cooker that comprises a hob with 4
> hot plates and one or two ovens - in this case you just have two ovens
> and you cannot apply that sort of diversity.

The main oven of our double oven has 3 elements - top, bottom and rear
for the fan. None of the settings use more than 2 elements and some only
one.
The top oven has 2 elements and only one of the 5 settings uses both.
Some settings only run the top elements at half power.
So it would seem reasonable to apply diversity, especially with the
thermostat creating an intermittent load as opposed to continuous running.

[Fredxx]

That is my point. In which case the instruction would advise accordingly.

Generally the terminal connections are away from an area of heat and so
no need to uprate the cable.

[Fredxx]

Wouldn't the rated power in the installation instructions take that into
account?

[Fredxx]

I meant from a max power the oven would take.

While I agree the thermostat should also reduce average current I'm not
sure how that should be applied to diversity. Currently I don't think it
is in any calculation.

[Brian Gaff (Sofa)]

There do seem to be a lot more combination ovens around these days that have
Microwave as part of their suite of facilities. I guess tis is a reaction to
more costly electricity, but many of those seem to plug in.
Brian

--

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Note this Signature is meaningless.!
"Jethro_uk" <jeth...@hotmailbin.com> wrote in message
news:svdl1i$4e2$1...@dont-email.me...

> Looking at a Hoover HO7DC3B308IN
>
> Hoovers website doesn't appear to have heard of it.
>
> Currys and Hughes (2 main stockists) don't seem to have a clue either
> (although to be fair to Hughes they did open a manual in store for me and
> we confirmed there is no specs about power supply).
>

> I'm guessing from the fact that it doesn't come with any cable means it
> needs to be wired into a dedicated circuit ? Which our kitchen has the
> remnants of from the CU. Just no feed from the wall.
>
> My impression is regs need the oven to be wired in directly - no plug ?
>

[newshound]

On 26/02/2022 18:26, ARW wrote:

>
> Why does the switch need to be red.
>
> From the Curry's site
>
> "ELECTRICAL INSTALLATION: This product requires professional
> installation to a dedicated cooker circuit (identified by a big red
> cooker switch) by a qualified installer, such as one of our Currys
> experts."
>
> A Scolmore CMA504 is not red
>
>

I see from reality shows that the "big red key" used by the police is
also often not red any more.

[Steve Walker]

Our double oven (two different ratings) has LEDs that go on when heating
and off when at temperature. It would be very easy to check the duty
cycle of each and work out the average load over a period of time.

Diversity is based on the idea of average load from the power and duty
cycles of all connected loads and the relatively slow rate of heating of
the cable when (temporarily) overloaded. It is just a way of estimating
an average load, without knowing all the details accurately.

[Steve Walker]

On 26/02/2022 19:05, John Rumm wrote:
> On 26/02/2022 16:38, Jethro_uk wrote:
>> Looking at a  Hoover HO7DC3B308IN
>>
>> Hoovers website doesn't appear to have heard of it.
>>
>> Currys and Hughes (2 main stockists) don't seem to have a clue either
>> (although to be fair to Hughes they did open a manual in store for me and
>> we confirmed there is no specs about power supply).
>
> B&Qs web site helpfully suggests the power output is 13W :-)
>
> (might be true if you only have the light on!)
>
>> I'm guessing from the fact that it doesn't come with any cable means it
>> needs to be wired into a dedicated circuit ? Which our kitchen has the
>> remnants of from the CU. Just no feed from the wall.
>>
>> My impression is regs need the oven to be wired in directly - no plug ?
>
> Yup - it does depend on the actual capacity. A double oven is very
> unlikely to be over 7kW, so a 32A protected radial will likely be more
> than adequate.
>
>> What sort of cabling is appropriate ? 4mm, 6mm ?
>
> Normal T&E as far as the isolator, and ideally a length of high temp
> flex for the final connection. Something like 2.5mm^2 H07RNF should be
> ok for the final connection. The T&E size being dictated by the length
> of the circuit and the any other de-rating factors encountered along the
> way.
>
> Chapter and verse here:
>
> http://wiki.diyfaq.org.uk/index.php/Calculating_A_Cable_Size

I think that my 22 feet of 16mm2 T&E to the cooker point might be a tad
oversized, but it *was* free :)

> (note that a typical "cooker" circuit wired in 4 or 6mm^2 cable will be
> more than adequate, since that will be specced to supply an over and hob
> combo, and it is usually the hob with the larger peak current draw)

Our double over is rated at 4.9kW peak load (it does also quote an
average of 0.79kWh per oven for its consumption, suggesting a duty cycle
of just over 32% on).

Our induction hob is rated at 7.3kW, but can take a peak of 9.7kW, for a
maximum of 10 minutes, if all four "rings" are heating and the two
largest are in "powerboost" mode (it automatically limits to two at a
time and and cuts back to normal full-power after 10 minutes).

So the hob is twice the peak load of the ovens - although I don't know
the duty cycle for the hob "rings" and so can't compare the average loads).

[Roger Mills]

On 26/02/2022 18:26, ARW wrote:

> On 26/02/2022 17:44, Roger Mills wrote:

>> I would expect it to need a dedicated radial circuit in (probably) 6mm
>> cable, connected to a 32A MCB and with an accessible isolator switch
>> near the oven.
>>
>> It sounds as if you've already got most of this. Is there a flush or
>> surface mounted cooker control unit with a big red switch (and
>> possibly a 13A outlet as well) with wiring going down to a cooker
>> outlet connection? If so, just connect the oven to this outlet.
>
> Why does the switch need to be red.

I'm sure it doesn't - but my impression is that most have been in the
past - and the OP's switch is probably red.


--
Cheers,
Roger

[#Paul]

Animal <tabb...@gmail.com> wrote:
> ampacity

Really?

#Paul

[Paul]

Strangely... yes.

It's not a term from university.

But it is used on the job, if you work
with infrastructure or power supply people
or component selection engineers.

Paul