wiring an electric oven - again
ijon tichy
I have a question regarding wiring an electric oven (3.7KW). the hob
will be gas.
AFAIU, wiring it into an existing 30A ring circuit is out of the
question, since it already has microwave and a washing machine (2.2KW)
on it, as well as other appliances like TVs, kettles, computers etc (the
existing ring covers the whole floor).
so it looks like I have to use a new MCB and a new circuit for the oven
alone. the question is whether I should run a single piece of cable to
it or create another ring circuit that would have the oven and maybe a
microwave on it. is ring suitable for the oven and the microwave? how do
I fuse connections to this new ring?
another question is what thickness of cable I need to use. for a radial
circuit it probably has to be 4.0mm and for a ring 2.5mm should be enough?
4.0mm is not easy to come across (screwfix doesn't seem to stock it), so
it goes up to 6.0mm which is probably an overkill. the distance from the
CU to the oven is 10-15m.
thanks a lot in advance for any suggestions.
/ijon
dennis@home
"ijon tichy" <sepul...@googlemail.com> wrote in message
news:g0mu38$2vdm$1...@energise.enta.net...
> 4.0mm is not easy to come across (screwfix doesn't seem to stock it), so
> it goes up to 6.0mm which is probably an overkill. the distance from the
> CU to the oven is 10-15m.
That would be because rings use 2.5 mm and 20A radials use 2.5 mm, not much
call for lots of 4 mm these days.
>
> thanks a lot in advance for any suggestions.
How many spare ways in the cu?
Run radials in 2.5 mm with mcbs. You should use a radial for a fixed 16A
load really.
>
>
Rob
My cooker has it's own circuit - 6mm cable running about 12m via a 40A
circuit breaker.
David Hansen
<sepul...@googlemail.com> wrote this:-
>so it looks like I have to use a new MCB and a new circuit for the oven
>alone.
I would suggest installing a proper cooker circuit, with at least a
30/32A protective device and suitably sized cable. That gives most
flexibility for the future in terms of cooking. Someone may want to
install a halogen hob.
An additional ring main is a separate issue.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54
John Rumm
> AFAIU, wiring it into an existing 30A ring circuit is out of the
> question, since it already has microwave and a washing machine (2.2KW)
> on it, as well as other appliances like TVs, kettles, computers etc (the
> existing ring covers the whole floor).
Agreed, a 16A point load that could be present for a reasonable duration
is also not really suited to a general purpose circuit such as you have.
> so it looks like I have to use a new MCB and a new circuit for the oven
> alone. the question is whether I should run a single piece of cable to
> it or create another ring circuit that would have the oven and maybe a
> microwave on it. is ring suitable for the oven and the microwave? how do
> I fuse connections to this new ring?
Ideally you want a new 16A radial for the oven alone. Then you will need
no further fusing on the circuit to protect the oven. The microwave will
probably be a smallish load, and can go on a normal socket on the ring.
> another question is what thickness of cable I need to use. for a radial
> circuit it probably has to be 4.0mm and for a ring 2.5mm should be enough?
2.5mm^2 is adequate unless you have to run through thermal insulation on
any high temperature areas on the way to the cooker.
> 4.0mm is not easy to come across (screwfix doesn't seem to stock it), so
> it goes up to 6.0mm which is probably an overkill. the distance from the
> CU to the oven is 10-15m.
4mm^2 is not a very useful size because although it has a higher current
carrying capacity, it does not have a larger earth conductor to match.
Hence there are often times where one might want to use it, but have to
use 6mm^2 just to get a more substantial earth.
--
Cheers,
John.
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ijon tichy
replying to Dennis' question, I only have one spare MCB left. 8(
John Rumm wrote:
> Agreed, a 16A point load that could be present for a reasonable duration
> is also not really suited to a general purpose circuit such as you have.
these new ovens are weird. I think as long as they have the circular
element around the fan and top grills, they fall below 3KW. as soon as
the bottom heating element appears, they go above. ~2.5KW for the fan
element plus 1KW for the bottom.
> Ideally you want a new 16A radial for the oven alone. Then you will need
> no further fusing on the circuit to protect the oven. The microwave will
> probably be a smallish load, and can go on a normal socket on the ring.
yeah, this is probably the route I am going to take.
16A radial is just 2.5mm then? AFAIK, this kind of setup is used for hot
water cylinders (20A), with corresponding unfused DP switches (red ones)?
> 2.5mm^2 is adequate unless you have to run through thermal insulation on
> any high temperature areas on the way to the cooker.
no, it will be away from the heat, buried under the plaster though. can
I put a thick rubber flex between the oven's terminals and the end of
the radial with a switch? this is probably a meter from the oven itself.
> Hence there are often times where one might want to use it, but have to
> use 6mm^2 just to get a more substantial earth.
I see. thanks very much again for all the explanations and suggestions.
/ijon
John Rumm
>> Agreed, a 16A point load that could be present for a reasonable
>> duration is also not really suited to a general purpose circuit such
>> as you have.
>
> these new ovens are weird. I think as long as they have the circular
> element around the fan and top grills, they fall below 3KW. as soon as
> the bottom heating element appears, they go above. ~2.5KW for the fan
> element plus 1KW for the bottom.
Single ovens often come with a plug on them these days - fully intending
that they be plugged into a normal socket. The load of an oven is not as
great as you might expect - especially when you take into account the
effect of the thermostat that will switch the load on an off once it is
up to temperature.
A double oven is another matter though and will normally be better
supplied from its own radial.
>> Ideally you want a new 16A radial for the oven alone. Then you will
>> need no further fusing on the circuit to protect the oven. The
>> microwave will probably be a smallish load, and can go on a normal
>> socket on the ring.
>
> yeah, this is probably the route I am going to take.
> 16A radial is just 2.5mm then? AFAIK, this kind of setup is used for hot
> water cylinders (20A), with corresponding unfused DP switches (red ones)?
Yup, you can fit a cooker point (the type without a socket), and a
cooker flex outlet. Ideally heat resistant rubber flex should be used
for the final connection - although T&E is often substituted.
>> 2.5mm^2 is adequate unless you have to run through thermal insulation
>> on any high temperature areas on the way to the cooker.
>
> no, it will be away from the heat, buried under the plaster though. can
Under plaster is the same as clipped directly to the surface from the
point of view of the current carrying capacity of the cable.
ijon tichy
> Single ovens often come with a plug on them these days - fully intending
> that they be plugged into a normal socket. The load of an oven is not as
> great as you might expect - especially when you take into account the
> effect of the thermostat that will switch the load on an off once it is
> up to temperature.
the oven I am referring to is just a powerful domestic single oven (neff
b1442), but it is still 3.7KW. this is not uncommon, since recently I
came across a siemens single oven that was 3.8KW.
> A double oven is another matter though and will normally be better
> supplied from its own radial.
it looks like I still have to do the radial for mine.
> Yup, you can fit a cooker point (the type without a socket), and a
> cooker flex outlet. Ideally heat resistant rubber flex should be used
> for the final connection - although T&E is often substituted.
yeah, I will use the flex, assuming I can buy a couple of meters of it
in Maplin.
thanks!
/max
ARWadworth
> John Rumm wrote:
>
>> Single ovens often come with a plug on them these days - fully intending
>> that they be plugged into a normal socket. The load of an oven is not as
>> great as you might expect - especially when you take into account the
>> effect of the thermostat that will switch the load on an off once it is
>> up to temperature.
>
> the oven I am referring to is just a powerful domestic single oven (neff
> b1442), but it is still 3.7KW. this is not uncommon, since recently I came
> across a siemens single oven that was 3.8KW.
>
>> A double oven is another matter though and will normally be better
>> supplied from its own radial.
>
> it looks like I still have to do the radial for mine.
You will need the radail circuit. And 3.8kW single ovens do seem quite
common. I used 2.5 T&E for the last one but the CU was only a metre from the
oven.
>> Yup, you can fit a cooker point (the type without a socket), and a cooker
>> flex outlet. Ideally heat resistant rubber flex should be used for the
>> final connection - although T&E is often substituted.
>
> yeah, I will use the flex, assuming I can buy a couple of meters of it in
> Maplin.
City Electrical Factors usually do well in stocking and cutting the flex by
the metre that you need.
Adam
John Rumm
> the oven I am referring to is just a powerful domestic single oven (neff
> b1442), but it is still 3.7KW. this is not uncommon, since recently I
> came across a siemens single oven that was 3.8KW.
Yup, so radial it is then. Some can be as low as 2kW...
ijon tichy
> Yup, so radial it is then. Some can be as low as 2kW...
just finished laying the radial. 2.5mm T&E for ~12m. should be plenty I
think just for the oven.
thanks for the contributions!
/ijon