Installing a 14.8kw Range Cooker

[drhmnd]

I am having a new kitchen fitted and replacing the electric oven/gas hob with an all electric Range cooker with a quoted max rating of 14.8kw. This will be on the opposite side of the kitchen to the previous oven. I was surprised to learn that my electrician plans to use the existing 6mm cable from consumer unit to isolator switch (around 18 Feet)and run a 6mm cable from it (about 20 feet) to the new cooker. The manufacturer gives a max rating of 7.43kw to the hob leaving 7.37kw for the two ovens. Our kettle is rated at 2.45 - 3kw. My view is that it will be too easy to overload this circuit on a big cooking day (xmas?) by switching on both ovens (30A) boiling a kettle at the isolator socket (12A) and frying an egg on the 2.02kw plate (8.4A). Thats a total of 50.4A. What would the voltage drop be over this installation? I am a complete novice but feel I need a 10mm cable to this cooker. I have yet to have this out with him as a lot of the prelim wiring has been done and the kitchen is fitted starting next week. I request comments from qualified electricians please, to assist in my argument. I did ring the manufacturers and they said that using diversity 6mm "should be alright" but then said they were not electricians!
Please reply ASAP before it may be too late.

 

[ColJack]

tell your electrician he's an idiot..

you need a new 10mm cable to a new isolator located within 2m of the cooker and in a position that is both visible and accessible..
the existing isolator on the oposite side of the kitchen is most probably not within 2M of the new range..

how big is your kitchen?

the breaker will probably need uprating to 63 amps also.. ( 14.8KW / 230 = 64.3A.. 14.8KW / 240 = 61.7A.. )

and do not fit an isolator with a socket.. there should be plenty of other sockets to boil the kettle off..

 

[drhmnd]

The kitchen is just under 3M by 4.2M and the isolator is exactly oposite the new cooker position in the 3M direction.

I believe that my electrician said the isolator was OK as it had to be within 3M?

Are you 'Part P' qualified - just so I know the quality of your advice?

I don't think my man is but intend to ask for a Completion Certificate signed by one - not asking you of course!

 

[ColJack]

I am not personally registered part P as I do industrial / comercial installations rather than domestic..

I am qualified to C&G 236 parts 1 and 2 as well as C&G 2380 inspection and testing.

if your man is not part P registered ( no such thing as qualified Part P..) then he shouldn't be doing the work unless he's notified the LABC..

no good electrician will sign off for other proples work unless they come and inspect the wiring routes and cable selections etc before plastering and so on..

It's 2m not 3 and the cable and breaker needs upgrading also.. the cooker switch itself is probably not rated for the appliance as they tend to be in the order of 45A

if you yourself are not happy with what he's sugested and would rather he fitted a larger cable (as you say in your original post.. ) then tell him that..
it's your house, your money and most of all your peice of mind...

 

[Adam_151]

Are you 'Part P' qualified - just so I know the quality of your advice?

, no such thing as a Part P qualification my friend!, what you are perhaps meaning, is is Coljack registered with an electrical industry body in order to self certify his electrical work complies with all relevant parts of the building regs? (and its not just part P thats relevant, of hand, parts A (structure) ,B (fire safety), L (energy efficency), M (accesibilty) and P (elec safety) are relevant and theres probbaly a few others!)

I don't think my man is but intend to ask for a Completion Certificate signed by one - not asking you of course!

If you want a building regs compliance certificate, then its going to have to come from the LABC themselves. An electrician who is registered with a body can self certify work done by himself, an employee or a subcontractor to LABC (meaning they dont have to come out and look at it) You electrician should be issueing you an electrical installation certificate, but if he is not registered, then its going to be notify to LABC directly time!

 

[drhmnd]

Thank you all for your experinced help.

I now know what to insist on - I think.

A new run of 10mm from a 62A breaker through an isolation switch mounted correctly within 2M of the appliance. I only hope the electrician does not storm off and leave me in the lurch when I broach the subject on Monday.

Regarding certification. I only want what is required when and if we ever sell the house as I believe that you now have to properly account for any work done to the electrics. Am I right and if so what is needed and who can issue it as it sounds very complicated and no doubt expensive and time consuming to go through the official channels mentioned.

I believe this electrician has been in the business for 30 odd years and should know what he is doing. Would he be able to issue something for the work done that would satisfy everyone? I am hoping that he is Part P registered or has notified the LABC as you suggest he should have... Unfortunately he does not seem to be contactable this weekend.

If anyone can enlighten me a little further on the above points I would be grateful.

I will keep you up to date with events next week!

Many thanks.

 

[Jaymack]

I would also check the supplier's main fuse size is adequate - may need uprating. If it has a seal on it, the "electrician" shouldn't break it without permission, alternatively, he can ask the DNO to confirm the rating.
The diversity for the cable size calculation can be calculated from the OSG, your electrician should know what this is.

 

[RF Lighting]

Are you 'Part P' qualified - just so I know the quality of your advice?

There are plenty of self certifying "electricians" out there that do not know their R's from their elbow.

Likewise there are lots of electricians who are more than competant to be carring out electrcal installation work, who are not registered to self certify.

I used to self certify, and now I can't. Where does that put me?

 

[drhmnd]

The suppliers main fuse at the meter is 100A - Type IIB - if that helps. At the consumer unit their is a 80A RCCB but I wouldn't know if the cooker circuit goes through it. We don't have any other high consumption appliances such as showers so I think these ratings should be adequate?

The final question in all this is: - What sort of record or certificate do I need to obtain from my electrician for the work done to avoid any problems in the future if, for example, the house is sold. Is it right that a buyers solicitor could ask for certain documentation? Is any particular paperwork needed as I have heard that you can no longer even move a 13A socket yourself, unless qualified - whatever that means.

For myself I am not bothered about his formal qualifications as long as he does a safe job that can properly take the load.

Thanks again

 

[ebee]

63 Amps!
No No No.
Not required.
First establish the KW rating at 240V if that is what your cooker is rated at.
If it`s 14.8 at 240 volt then 61.67 Amps.
But the standard cooker arrangement is to allow diversity as (with perhaps the odd exception such as xmas day) you never use all of it at once (and thermostats sometimes take some heating out of circuits at differing times too).
Standard arrangement is.
the first 10 Amps plus 30% of all the rest plus 5Amps if a socket is on the control unit for ocaisional use of a kettle.

This gives a demand of 25.5 at 240V or 30.5 if socket on board.

or

26.3 at 230 or 31.3 if socket on board.

6.0 mm cable should suffice if no other derating factors are present.

However,. as a rule of thumb, 6.0 cable will generally be OK for up to 13KW thought should be given to 10.00mm cable.

Personally 10.0mm and a 40A MCB would be my choice (and I don`t like having a socket on the control unit as it`s a thro back to olden days when folk didn`t have enough sockets).

It might be difficult to rightly condemn the 6.0mm

 

[ColJack]

i don't like applying diversity to fuse/breaker ratings..
when all the heating elements are turned on at the same time (IE starting the vegies boiling while pre-heating the ovens ), then the current draw will be close to the maximum demand until the thermostats kick in and start cycling..
at which point the 40A breaker you prescribe will undoubtedly trip..
maybe not every time but it WILL blow on occasion..

cable sizes I will bend a little on.. as the heating effect of a short term overload will dissipate once it starts cycling..

there is no need to "condemn" the cable.. the customer has the right to demand that a larger cable be put in if thats what they've been advised or what they want..

if they ask for a smaller cable then you can refuse on the grounds of safety..

 

[ebee]

Yes I am pretty much in agreement .
Even on Xmas day etc the MCB is unlikely to trip though.
However, if the electrician has said he will do it and it is safe and/or it complies with all relevant regs/laws then he might refuse to alter it and demand payment or alternatively charge extra for the work.

Example - a customer might want supp bonding in a bathroom in 10.00mm or 6.0mm but youve already done 4.0mm which will almost always comply.
Would you change it?
or insisted your 1.0 lighting was redone in 1.5 (or even 2.5 Agghh)

 

[ColJack]

if you can provide the make and model then we can look up the tech specs and tell you exactly what size breaker and cable you need...

 

[drhmnd]

The cooker is made by Rangemaster - part of the AGA Group. The model is Elan 90 with Ceramic Hob.

The brochure gives power ratings for the hob of 2 @ 1.1kw, 1 @ 1.56kw, 1 @ 1.65kw 1 @ 2.02kw. Total hob rating 7.43kw

For the whole cooker it states a max electrical load @ 230V of 14.8kw.

No detail is given about the ovens but from the above I deduce that the two ovens together would peak at 7.37kw.

I can see the situation where both the ovens are switched on at the same time as the two highest output hob rings and I make that almost exactly 48A @ 230V. [

Would this overload the 6mm/45A breaker circuit before the thermostats start to cycle? I don't want to be resetting the breaker at regular intervals. For one reason I suppose it might then wear and one day (in the middle of a big cook) it may refuse to reset.

Any further comments would be greatly appreciated.

 

[banip]

I am not personally registered part P as I do industrial / comercial installations rather than domestic..

I am qualified to C&G 236 parts 1 and 2 as well as C&G 2380 inspection and testing.

if your man is not part P registered ( no such thing as qualified Part P..) then he shouldn't be doing the work unless he's notified the LABC..

no good electrician will sign off for other proples work unless they come and inspect the wiring routes and cable selections etc before plastering and so on..

It's 2m not 3 and the cable and breaker needs upgrading also.. the cooker switch itself is probably not rated for the appliance as they tend to be in the order of 45A

if you yourself are not happy with what he's sugested and would rather he fitted a larger cable (as you say in your original post.. ) then tell him that..
it's your house, your money and most of all your peice of mind...