Wiring for a new kitchen installation

[vetinry]

Good evening everyone

I am busy renovating a house that we have recently purchased and as soon as I've fitted the underfloor heating and the floor has been screeded, I will be installing a new kitchen.

As part of the new installation, we are having 2 NEFF ovens, and an induction hob which will be installed on a central island.

I've had a look at the existing wiring and as far as I can tell, there is 10mm2 cable coming into the kitchen from the main consumer unit, which is in the garage. The way I've established this is to measure the full cable in the garage (approx 17mm x 9mm) and the live cable in the CCU (6mm diameter including the red insulation)

The cable run is about 25m from consumer unit to Kitchen and is laid on top of the joists in the loft.

My new appliances have the following ratings

Power Current
Oven 1 3600 15
Oven 2 3600 15
Hob 7200 30
Drawer 800 3

Total 15200 63

I've calculated diversity (10% total plus 30% of what's left) as 26 amps but I would rather not rely on this because at busy periods (Christmas etc) I imagine that the current draw will be towards the top end.

Currently, there is a 30amp MCB in the main control unit and I'd like to increase this assuming it's ok to do so.

But in the kitchen itself, I am trying to work out the best way to wire all these in.

Is it ok to install a second consumer unit (in cupboard above one of the ovens) and then put some smaller MCBs to split the load to each of the 2 ovens and hob.

To reduce the overall load, I will probably wire the warming drawer into the ring main rather than use the cooker circuit.

Assuming what I'm suggesting is not completely mad, what size cable would you recommend I use from the CU in the kitchen to each of the ovens and the hob.

And finally, I am going to lay the cable to the hob under the floor - should I use conduit, and if not, is the cable ok unprotected (it will be laid in the insulation layer) or could I use some armoured cable?

Sorry about all the questions - any help you can offer would be very much appreciated.

Cheers

Steve

 

[sparkiedave]

Shall I be the first to mention LABC? Part P etc?

 

[vetinry]

I'm assuming you're saying that because of the need to have this work completed by a qualified electrician

I was planning to get one in to do the final wiring in and check my plans, but I'm always interested in the projects I'm working on, hence all of my questions.

But point taken

Steve

 

[mbga9pgf]

I'm assuming you're saying that because of the need to have this work completed by a qualified electrician

I was planning to get one in to do the final wiring in and check my plans, but I'm always interested in the projects I'm working on, hence all of my questions.

But point taken

Steve

Its 10 Amps + 30%. Which by my calcs = 29A. This assumes that you are wiring into a terminal and not simply plugging in the cooker to the wall!

The diversity rule plays a part as the cooker/oven will not be maintaining 100% output the whole time, even if you have all the hobs and oven are selected on. Reason being, the hobs cycle on and off, and are not on continuously. Same with the oven. 6mm^2 assuming you are clipping direct or in insulation, according to this:
http://www.tlc-direct.co.uk/Figures/Tab4.7.htm

should be good enough.

Other point to remember is your MCB will not trip at the rated value, it will go on for a long while depending on the overcurrent value before it trips.

http://www.voltimum.co.uk/news/1826/cm/selecting-the-right-mcb-----its-as-easy-as-bcd-.html

* Type B devices are designed to trip at fault currents of 3-5 times rated current (In). For example a 10A device will trip at 30-50A.

You may well find your 30A MCB with 6mm^2 cable is fine, the only stopper will be if your cooker supply wire is buried in a wall full of cavity insulation.

 

[ban-all-sheds]

I was planning to get one in to do the final wiring in and check my plans, but I'm always interested in the projects I'm working on, hence all of my questions.

Then find your electrician first, and ask him all these questions.

There's no point you deciding on the cable size and MCB rating for the cooker circuit if he doesn't agree.

There's no point you installing a 2nd CU in a cupboard if he doesn't like that idea.

There's no point anybody here choosing cable sizes, as your electrician will be the one taking responsibility for the design.

There's no point you, or anybody here, deciding how to install the cable to the island if your electrician has other ideas. You should find out from him about that cable asap, in case it has to go in before the UFH. Is that a wet system, or electric?


One man's story of getting an electrician involved too late: //www.diynot.com/forums/viewtopic.php?t=233382

 

[mbga9pgf]

Actually an example of someone rushing headlong int something without referi g tothe regs and checking his understanding of matters. If he had bothered to do both, he would have been fine. Why can't you agree his current installation is fine for his requirements According to th regs?

Or do you get off on the whole knowledge is power thing?

 

[uzziel49]

I've been preparing for a kitchen project myself. As I understand it, the electrician providing the part P cert is taking responsibility for all of the electrical work undertaken, not just what he himself has done. If he issues the cert but hasn't done the work, and there's any come back, then he's responsible. That's why the electrician needs to be involved at the top to approve design, and why they'll likely want to do all of the work themselves. It's not simply a matter of complying with building regs, it's about compliance and responsibility in this overly litiginous society we've adopted from our former colony.

At least, that's how I understand it.

 

[vetinry]

Thanks for all the replies.

I didn't realise that this would open such a can of worms.

I'm absolutely aware of the need for an electrician to be fully involved with this project.

There are 2 things that drive my interest. Firstly a natural desire to understand exactly how things work - I just have a thirst for knowledge which extends across everything I'm involved with.
Secondly, I have been let down by a variety of trades previously, and I suppose this has created a lack of trust which means I like to have a pretty good handle on what is going to be done. I'm sure that will annoy the hell out of some of you, and I also know that most trades people are credible and trustworthy.

So this is why I have bothered to read up on diversity, on CUs, CCU, cable ratings in and out of insulation, MCBs etc. I'm now going to read Part P as well, to try and be as well informed as I can be.

Steve

 

[Gees]

Thanks for all the replies.

I didn't realise that this would open such a can of worms.

I'm absolutely aware of the need for an electrician to be fully involved with this project.

There are 2 things that drive my interest. Firstly a natural desire to understand exactly how things work - I just have a thirst for knowledge which extends across everything I'm involved with.
Secondly, I have been let down by a variety of trades previously, and I suppose this has created a lack of trust which means I like to have a pretty good handle on what is going to be done. I'm sure that will annoy the hell out of some of you, and I also know that most trades people are credible and trustworthy.

So this is why I have bothered to read up on diversity, on CUs, CCU, cable ratings in and out of insulation, MCBs etc. I'm now going to read Part P as well, to try and be as well informed as I can be.

Steve

I absolutly agree with what you have written above. If you have some knowledge of a subject it certainly helps when you get ridiculous quotes for jobs you need doing. Especially when you "act dumb" and just listen to the things you are told by so-called professionals. Not only in the electrical trades but almost all trades have these con artists who will take you for all youve got if your not carefull.

 

[ban-all-sheds]

Actually an example of someone rushing headlong int something without referi g tothe regs and checking his understanding of matters. If he had bothered to do both, he would have been fine. Why can't you agree his current installation is fine for his requirements According to th regs?

Because I've not seen it, so I don't know if it is fine for any requirements nor if it complies with the regulations. I do know that an electrician has seen it and has determined that it does not.

Or do you get off on the whole knowledge is power thing?

If knowledge is power then I regularly encourage people to empower themselves by providing them with routes to acquire knowledge.

 

[ban-all-sheds]

I'm absolutely aware of the need for an electrician to be fully involved with this project.

OK.

It's just that at first it didn't look that way - it seemed that you were saying that you were going to be making circuit design decisions and installing cables etc:

Is it ok to install a second consumer unit
.
.
.
I will probably wire...
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.
.
what size cable would you recommend I use....
.
.
.
And finally, I am going to lay the cable to the hob under the floor...

and then planning to get an electrician to come along, connect them up, and (presumably?) sign a legal document to say that he'd done all of the design and installation:

I was planning to get one in to do the final wiring in and check my plans

People here were just trying to warn you that it doesn't work like that.

IMO of particular concern is this:

as soon as I've fitted the underfloor heating and the floor has been screeded, I will be installing a new kitchen.

I think you should get your electrician involved before that stage, in case installing the floor causes problems when you come to run the cable to the island.

There's also the design of the island, and its relative position to consider. Where will the isolator for the hob go, for example?

There are 2 things that drive my interest. Firstly a natural desire to understand exactly how things work - I just have a thirst for knowledge which extends across everything I'm involved with.
Secondly, I have been let down by a variety of trades previously, and I suppose this has created a lack of trust which means I like to have a pretty good handle on what is going to be done. I'm sure that will annoy the hell out of some of you, and I also know that most trades people are credible and trustworthy.

So this is why I have bothered to read up on diversity, on CUs, CCU, cable ratings in and out of insulation, MCBs etc.

Fair enough, but you're going to need to know quite a bit if you want to be able to successfully vet your electrician's design and challenge things you don't like.

Just like doing your own design and installation, it is no use thinking that all you have to do is to ask the questions which happen to occur to you - you need to acquire a genuinely competent level of knowledge and understanding.

//www.diynot.com/wiki/electrics:books

I'm now going to read Part P as well, to try and be as well informed as I can be.

This is Part P:

You should also read all of the Building Regulations to find out about the requirements for notification.

Bear in mind that Approved Document P is not "Part P", it is not the law, it is not mandatory, it has never accurately reflected the law, and what it says about LABC charges is now wrong because of more recent legislation.

 

[shazam]

So this is where you've been hiding BAS. Arrogant as ever I see.

 

[ban-all-sheds]

I would ask you to provide a rational analysis of what I have written here (and only of what I have written here , i.e. not involving any products of your defective imagination) which would justify a tag of "arrogant", but there'd be no point would there.

Particularly as 100% of your posts here so far show that the only reason you have joined is to criticise people, and that you are at least partly motivated by past grievances from other sites.

 

[shazam]

BAS: We don't know each other, we've never spoken to each other on a forum or away from a forum. I said you're arrogant because I have indeed been a member of forums you have been and you always (to me) come across as arrogant and in some cases condescending. In this case I feel that you are talking down to the OP and that you come across as arrogant. Now you can feel free to correct me here if I'm wrong. I was under the impression that you yourself are not a qualified electrician, so I find it odd that if this is true, you're here giving advice. Like I said, you can correct me if I'm wrong and I'll be big enough to apologize for my assumption.

You take me as you find me BAS, If I think something, I'll come right out and say it rightly or wrongly, but please don't think I've come here to fight anyone because I haven't. As to the 100% of posts are to criticize people, well that 100% was 2 posts. Just to put the record straight, I wasn't criticizing the other forum member in my other post, I was outright telling him he's wrong to support and blindly defend a certain scheme provider. In that instance, I believe I had more experience of said provider than he.

For the record, I don't have a defective imagination, I call things as I see them, that's all.

 

[Electrifying]

There are 2 things that drive my interest. Firstly a natural desire to understand exactly how things work - I just have a thirst for knowledge which extends across everything I'm involved with.
Secondly, I have been let down by a variety of trades previously, and I suppose this has created a lack of trust which means I like to have a pretty good handle on what is going to be done. I'm sure that will annoy the hell out of some of you, and I also know that most trades people are credible and trustworthy.


Steve

Ha Ha, every tradesman's dream - He'll be up the ladder behind you