Any electricians on here.

[MikeS]

Long story short. Ordered a new Zanussi gas oven but they delivered a better electic double oven with induction hob.

Total kw 12.9 and manual says to use 6mm2 cable. Fuse at 30amps

Rough math gives 53amps and even with diversity seems a lot for cable rated at 7kw or around 45amps.

Should I go with 10mm2 cable or follow the manual.

Mike

[Former Member]

[This posting has been removed]

[Paul Marsh]

Depends on long your run of cable is. The longer it is, the higher rated cable it has to be. Although your 10mm2 cable will be more than enough - it can handle 63A.

Just make sure you use a "D" or "C" type MCB, preferably, not a fuse. Might be worthwhile looking at your total incoming supply current limit, usually 100A. Worse case scenario, you have full load on the oven at Christmas, someone has a shower and have a few electric heaters on - all could go up on Xmas day.

[Andy48]

I run a double electric oven and an induction hob on a longish 6mm cable with a 32amp MCB. Never had a problem, and never tripped the MCB. Add to that our voltage coming into the house is extremely high, 254v the electricity board noted recently (they are monitoring it). This high voltage also has the effect of increasing the current. Also we only have a 60amp main incoming fuse.

Do remember, it is very unlikely that all four hobs, and both ovens will be calling for full power at exactly the same time, hence your comment about diversity.

There is quite an issue with power factor on induction hobs. Google it, it is very complex but basically the actual power they use is different to the theoretical power (ie volts times amps) they use.

[Chris Bott - Moderator]

Don't forget the special saucepans you'll need for induction too, MikeS.

[Andy48]

Blow the saucepans... the frying pan is the important one!

[Andy G.]

Andy48... raising the voltage will LOWER the current draw!!

Power factor, put simply, inductive load the current will take longer to pass through the load than the voltage will, thus causing a trailing power factor, this means that the Peaks of each will not coincide so multiplying the current x voltage will not give the correct value. It will give Watts but you need to be looking for '''volt amperes''' which is achieved by Volts x Amperes x power factor. I.e 240x28x0.93 . A capacitive load has the opposite effect.. 

Edited By Andy G. on 07/12/2015 09:10:12

[Mike Etheridge 1]

Not sure about your theory Andy G even though my brain is now rusty.

I agree most inductive circuits such as cookers etc produce a lagging power factor (Cos Thi L) and that capacitive circuits produce a leading power factor. it is most unlikely however that any domestic installation will have anything but an inductive load.

Regardless of power factor in an electrical circuit the current which is a variable is determined by dividing the circuit voltage which is normally constant by the resistance which is a constant (Ohms Law). If the voltage is increased then so must the resultant current be increased.

We had instances in large installations such as colleges and swimming pools where the Electricity Authorities would charge for the KVA used which was given by the vector sum of the KW (useful power kilowatts) and the KVAr (Wasted power reactive).

[Daren Graham - Cambria Funfighters]

Posted by MikeS on 06/12/2015 20:36:06:
Long story short. Ordered a new Zanussi gas oven but they delivered a better electic double oven with induction hob.

Total kw 12.9 and manual says to use 6mm2 cable. Fuse at 30amps

Rough math gives 53amps and even with diversity seems a lot for cable rated at 7kw or around 45amps.

Should I go with 10mm2 cable or follow the manual.

Mike

If in doubt just go with the larger cable but make sure it goes all the way back to the fuseboard, not jus to the existing cooker point. a 32 amp breaker is fine and even if this is not man enough it will trip regularly but still do its job, then you can upgrade it with a larger breaker for less than £10.00

[Martin Whybrow]

Posted by Mike Etheridge 1 on 07/12/2015 10:11:17:

Regardless of power factor in an electrical circuit the current which is a variable is determined by dividing the circuit voltage which is normally constant by the resistance which is a constant (Ohms Law). If the voltage is increased then so must the resultant current be increased.

That applies to resistive and reactive loads; an induction hob is a completely different matter, it's essentially a switch mode power supply driving big inductors, so the power is constant and current does indeed drop as the voltage goes up.

[MikeS]

Thanks for all the replys. My set up is as Mike Etheridge describes.

Main cooker switch with 13amp socket on the wall near oven above work top. Cooker outlet plate behind oven.

Consumer until is 18ft approx from cooker switch with a b32 fuse with on/off switch.

 

Oven outlet plate

Info regarding cooker wiring

Cosumer unit cooker switch.

Edited By MikeS on 07/12/2015 16:06:04

Edited By MikeS on 07/12/2015 16:07:17

[Andy48]

Posted by Martin Whybrow on 07/12/2015 12:38:25:

Posted by Mike Etheridge 1 on 07/12/2015 10:11:17:

Regardless of power factor in an electrical circuit the current which is a variable is determined by dividing the circuit voltage which is normally constant by the resistance which is a constant (Ohms Law). If the voltage is increased then so must the resultant current be increased.

That applies to resistive and reactive loads; an induction hob is a completely different matter, it's essentially a switch mode power supply driving big inductors, so the power is constant and current does indeed drop as the voltage goes up.

Remember I was talking about an induction hob, AND a double oven. While the hob may be regulated to provide a constant power irrespective of the input voltage, the oven will be a resistive load, although the current drawn by the oven will be less than the hob.

[Mike Etheridge 1]

I had better check out induction hobs-interesting!

But of course over voltage can cause problems with an electrical installations particularly with the reduction of lamp life. We had a school new build extension project which meant that the building had to have a new electricity supply. Once completed the emergency luminaires failed and had to be replaced as a result of over-voltage, something the electricity authority did not appear to check at the time of switch-on of the new power supply. 

 

Edited By Mike Etheridge 1 on 07/12/2015 17:34:43

[Paul Marsh]

Posted by Mike Etheridge 1 on 07/12/2015 10:11:17:

Not sure about your theory Andy G even though my brain is now rusty.

I agree most inductive circuits such as cookers etc produce a lagging power factor (Cos Thi L) and that capacitive circuits produce a leading power factor. it is most unlikely however that any domestic installation will have anything but an inductive load.

Regardless of power factor in an electrical circuit the current which is a variable is determined by dividing the circuit voltage which is normally constant by the resistance which is a constant (Ohms Law). If the voltage is increased then so must the resultant current be increased.

We had instances in large installations such as colleges and swimming pools where the Electricity Authorities would charge for the KVA used which was given by the vector sum of the KW (useful power kilowatts) and the KVAr (Wasted power reactive).

That's where Power Factor Correction comes in. We do loads for colleges, probably done yours and if a inductive load is expective, Power Reactors are also included within the P.F.C. This is usually to stop the capacitors getting a hammering, and have had them blow up as a result. You should see the mess I've had to clean up!!! Electrolite everywhere, that's if you don't have a fire...

[Mike Etheridge 1]

That is right Paul power factor correction equipment was fitted in swimming pools where CHP units replaced boilers. Capacitor banks were used to produce an almost unity power factors on the installations. Eventually the CHP installation packages included power factor correction equipment. Not sure what happened on the college jobs?

I seem to remember being told that alternators which have leading power factors were used by Electricity Authorities to correct power factors on their supplies. As such the alternators were called synchronous capacitors. I never saw any of those installations though. (it seems that synchronous motors are used rather than alternators?-needs checking)

Edited By Mike Etheridge 1 on 08/12/2015 00:24:45

[ted hughes]

I recently fitted two Electric ovens, a B&Q own brand and a Zanussi.Both came with their own cables which plugged into the oven and were fed from a recommended 30 amp fuse which took just a few minutes to wire.

[MikeS]

Thanks Ted. This one states it is not supplied with cable.

A little inconvenient
of the manufacturer but I can see why they wouldn't.

I posted photos of my consumer box, wiring information and wiring plate. I just to confirm that this is ok before my electrician arrives so I now what to expect. Mike

[ted hughes]

Pic here:

Edited By ted hughes on 08/12/2015 08:36:21

Actually, I don't know how to upload pictures!

Edited By ted hughes on 08/12/2015 08:39:56

[Mike Etheridge 1]

Mike S

Everything looks OK to me with your cooker circuit listed as number 8 circuit and not linked to the RCD side of the consumer unit. As your cooker only has a 30 amp requirement I cannot think of any reason why the existing circuit needs any change. That said I would expect the electrician to test the circuit and present a certificate and if he uses any cable with European colours I would expect him to label your consumer accordingly.

Someone mentioned about the electrical services to homes being rated at 100 amps and that the electricity loads in homes can almost reach that value. This may be true but most electricity authorities use coarse rated fuses in their cut-outs which can take a 100% overload for up to 4 hours. In blocks of flats some of the electricity boards fuses are only rated at 60 amps. When these flats are re-wired often electricity boards insist that these fuses are uprated to 100 amps. The lateral mains (Or sub-main) cables that serve the flats from the electricity board's fuses are often contained in buried imperial sized conduits that also provide earthing. These conduits are not big enough for 25mm2 cables to be installed with earth wires (CPC's) to suit 100 amp fuses so by special arrangement the electricity board fuses have to be retained at 60 amps and 16 mm2 cables used. It was always felt that flats would only have 30/32 amp cooker circuits and this was necessary as when flats were rewired the kitchen ring circuit and cooker circuit cables were drawn into the existing 25 mm / 1 inch conduits. Any cables larger than 6mm2 could not be drawn into the conduits. However there is no reason why 45 amp cooker switches cannot be attached to consumer unit 32 amp MCB's.

[Codename-John]

You can see clearly from the photo`s that the circuit labelled "cooker" is on the RCD side, and on the consumer unit label you can clearly see just above the "N" on CAUTION it says RCD Operating current 30 mA

From what I understand all you wanted to know ( before the "designers" and mathematicians came along ) is can you connect your new cooker to the existing cooker connection using 6mm cable, The answer is yes, Its RCD protected and fused at 32 A so 6mm will be fine

Cooker circuit diversity is calculated to - 10A of total load plus 30% of remainder. Add additional 5A if cooker point socket is fitted.

12900 / 240 = 53.75

10A + (30% of the remaining 43.75) 13.125 that gives around 23 A without socket or 28 A with

Edited By Codename-John on 09/12/2015 18:08:30

Edited By Codename-John on 09/12/2015 18:23:45

[MikeS]

Mike and John. Thank you the information and also everyone else. I just wanted to have an idea of what was what etc for when the electrician arrives. Thanks again. Mike

[Pete B]

In the interest of balance and to prevent further personal attacks, I have deleted two posts. It serves as a reminder that advice given on a forum, whilst given in the best of intentions, will invariably generate an alternative view. Whether that view is projected in an acceptable manner is invariably down to the poster.

I'm sure MikeS will get the appropriate advice from his electrician who will be on the spot and best able to assess the installation, so I think it best to lock this thread now.

Pete