HELP...Kitchen wiring inadequacies??.

[Ceekay]

Sorry guys I'm sure these points have been raised before but been busy searching.

I have been sent a diagram by the shop where we purchased our kitchen for the electrical wiring requirements and positions. I am a electrician to the 17th edition by trade but it's not my every day job nowadays so I'm questioning myself and require some confirmation.

One of the items is a 7KW induction hob for the island and the drawing states a 2.5mm cable to the cuboard under the hob??. This is scary to me as I work this out at around 28A which I believe is around the max the cable could carry even without any factoring taken into consideration? There is some led lighting also on the island which I take they will supply from this cable but obviously that will be minimal (I take it this would need to be fused down?) but more importantly a 13A pop up socket has also been added to the island and therefore had just put this part of the installation well beyond what they have originally stated.

The second major point is the ovens and two of them. One is a standard fan oven rated at 3.45Kw and the other is a smaller microwave combination oven rated at 3.6KW so if im correct both together are roughly 7KW and therefore roughly 28A? On the drawing they are showing 1 standard 13A double socket outlet! Surely just one of these item exceeds the maximum as even a double outlet its max load is still 13A or 3KW there abouts no matter how many outlets you have as far as I'm aware they are still only rated 13A. So my point is that one oven is slightly over but the two ovens are definitely a no no even if they were to have plug tops on which as suggested by the shop may be the case? Not sure how an oven rated at 3.6KW can possibly have a plug on?

Thirdly the drawing states a 2.5mm cable to be left in cupboard below sink for both a 2.5Kw dishwasher and also a instant hot water tap which states it needs a 10A supply but is rated at 1.5Kw? These two items should be fine if they are using say a 20A putlet plate but I have been told to leave a cable as on the island so not sure?

Normally I would place a double pole switch for the dishwasher above the worktop and not sure where the local cooker point isolators will be for the ovens and hob? Is it ok to place these within a cupboard especially the under sink position? I also take it they will tap off at various points for the led lighting but as far as I'm aware this would need to be a fused spur downrated to 3A?

Anyway I have added the so called plans below and would really appreciate your help as I think it must be me going insane?

Many thanks, Keith

 

[telectrix]

with cooking appliances, the diversity factor is what come into play here . for an e.g. 7kW induction hob equates to 29A, but due to the cycling of thermostaically controlled elements, this would give you a design load of 10A + (30% of 19A), = 16A. still too much for a 13A socket on a RFC. i'd be inclined to run a 6mm T/E to each cooking appliance, fit each with a 45A isolator, then go from there when appliances are to be connected.

 

[spary]

you need to apply diversity factor to ovens

 

[Sintra]

I wouldn't be taking a kitchen fitters advice for cable sizing. Who will be signing off the design section of the electrical installation certificate?

 

[Wilko]

At my place I have silly mm2 in the kitchen so It doesn't ever disappoint, that would be toooo embarrassing. Much easier to go up a size now than later .

 

[bigspark17]

If your undertaking this job it will need to be signed off accordingly. Are you registered with one of the scheme prividers, if not how or who will be signing this off. Once this is clear members may be more forthcoming helping with some of the design issues.

 

[Andy78]

I'd be checking with the manufacturer's connection data regarding all the appliances. They know what diversity, and how they have built that diversity into their appliances, and what size cable they require for safe operation. It is invariably always smaller cable than required for the stated FLC, but do check. I have connected full electric hobs with 1.5mm, 2.5mm, and 4.0mm cable. I have also connected appliances that have no built in diversity as confirmed through current measurement.

 

[Andy78]

You don't get many of those in a cauldron.....

 

[telectrix]

yeah but only got 2 hands.

 

[Midwest]

You could have a look at the manufacturers manual to see what supply is required for each appliance. Most have to say, state 'consult a qualified electrician', but sometimes they give a clue to what their appliances consume, and supply required. My range cooker runs off a flex I'd be concerned about supplying a table lamp. Does take a long time to cook the Sunday Roast though?

 

[westward10]

You could have a look at the manufacturers manual to see what supply is required for each appliance. Most have to say, state 'consult a qualified electrician', but sometimes they give a clue to what their appliances consume, and supply required. My range cooker runs off a flex I'd be concerned about supplying a table lamp. Does take a long time to cook the Sunday Roast though?

Is it a coiled flex that will stop the current.

 

[Ceekay]

Many thanks for the reply's to date.
Up until a couple of years ago one of the companies I work for were NICEIC registered and obviously part P was automatic when a fully registered member but we let this go when we wound that side of the company down. I will be going through local building control to hopefully get this passed or one of my neighbours is an electrician and managers an electrical contractors so either way it will be completed through the appropriate channels and signed off accordingly as building control are on site anyhow for the extension itself that is hosing the said kitchen.

So are we saying that if the manufacturer has plug tops on both these ovens you would plug them into 1 13A double socket outlet supplied by a RFC ? I know you can apply 30% diversity to every amp over 10a but I'm dubious about this as I appreciate the ovens reach temp and then click on and off on the stat but if you have a large Sunday roast on fir many people and both ovens are trying achieve 200 degrees at the same time I'm betting you could start cooking your dinner on the double socket plate it would get that warm.

Anyone any thoughts on the 7Kw hob and a 13A pop up socket being on a 2.5mm cable? Surely not viable?

Also any thoughts on the isolators and sockets being inside the cupboards?

Thoughts also please to running cupboard led lighting and drivers, as my thoughts are that if this is to be powered off any of the kitchen appliances the it needs to be through a fused spur? I may even run a separate lighting feed completely for the under cupboard lighting so it doesn't get too messy?

Any further thoughts very much appreciated.

Cheers Keith

 

[telectrix]

any appliance over 2.2kW should be on it's own dedicated circuit, irrespective of the cable size, which should be calculated for each appliance , taking account of diversity, loop impedance, and volt drop. better to have an oversized cable than a melted undersized one.

 

[Midwest]

OP you've been given some good advice from members here. As it is your kitchen, I would follow the advice given and design & install suitable sized cables for each appliance, or combination of appliances.

Do bear in mind how these appliances work, cycling effect etc as already mentioned. My rather pathetic range cooker has a total power load of 3100w. However, the selector control switch only allows a maximum selection of two of the three elements at anyone time. Your oven/microwave will function in a similar way, but as telectrix advised, will still need a dedicated circuit. As Wilko advised, you may also need to consider 'future proofing' for supplies, should you replace appliances, i.e. don't install to the bear minimum, as being perhaps suggest by the kitchen company?

I did a kitchen refurb' recently, where a customer had purchased an all electric Aga range cooker. The Aga had been connected to an existing 32amp supply by Aga engineers. It had been happily used for a few months, until they decided to alter the kitchen, to accommodate their new cooker! When I checked it's spec', it had a total power rating of 16kw. A call to Aga, and they recommended a 45amp supply for their cooker. This would have exceeded the maximum load for the (local) CU supply, so I installed a larger supply cable, but kept the fusing to 32amp. Touch wood, they have been no issues.

 

[Ceekay]

Thanks again chaps much appreciated but I think you will find that the whole purpose of this post was because I disagreed with the drawings that were sent to me and wanted to confirm this so I could wire this as per most of the advice so the general confirmation is what I was after although if I place 2 45A isolators in for the ovens and the fitter turns up with plug tops on them it may void the warranty to cut them off?

Also not had any reply's really about any of the other problems mentioned as it seems to be all concentrated around the ovens? Any advice re the hob/socket on the island or the other points?

Many thanks