House Rewire

[scholesy]

Hi All

first of all thanks to all the posters on here as the advice I've read, been given, has been of great help to me.

I'm planning on doing a rewire of my home. I'm fully aware, (thanks to this site), of the fact the works notifiable and PartP regs etc. To give you some background, I've spent the last 6 months gathering information from this forum, trawling through the pages picking out useful bits of information. I've also bought several books (including IEE regs). Also in that time i've labelled all my current circuits in my house to the point where if you look at any cable under my floorboards you'll find its been labelled. So i've not taken this lightly and understand the dangers involved.

I've also now designed what circuits I want, calculated cable lengths, max demands etc...

Current layout -> 1 x 30A Ring Main, 1 x 30A Cooker, 2 x 5A Lighting (Up\Down)
Planned Layout -> 1 x 40A Cooker\Socket [6mm], 3 x 32A Ring Mains (Up\Down\Kitchen) [2.5mm] (RCD Protected), 3 x 6A Lighting (Up\Down\Outside) [1.5mm], 1 x 6A Smoke Alarms [1mm 3core+E]. May also include circuit for boiler rather than fuse spur of ring main.

I know a family friend who's an electrician. He will test\certify the work as long as he can follow all cables, (he will trust me on cables running through conduit). I'm going to change as much cable as I can without actually opening my fuse box, (just removing fuses, I know my limits), ie all lighting circuits apart from last length to fuse box. As much of the ring mains although this will be more difficult due to it being split into 3. Install all sockets, do chasing, run conduit. I'm hoping to get it to such a level wherby my electrician friend can come up for the day, swap the CU, attach the ends, test and certify.

I still have a few questions which I'm not 100% on. I don't wish to ask the family friend as I don't personally know him that well, but would appreciate any advice.

Questions

1) Does a complete rewire mean that the work is classed as a refurb, and therfore comes under Part M? Its just that all my upstairs sockets are positioned just above the skirting and i'd like to keep them their if possible, (rather than moving to 450mm).

2) Do cables running alongside joists have to be clipped? Its just that i've recently sanded\varnished my bedroom floorboards and am keen to avoid removing floorboards if possible. I was therfore planning on running a ring mains cable from the neighbouring room. This would run under the partition wall and alongside a joist to the far wall in my bedroom. Would this be OK?

3) My kitchen cooker is currently on a 30A fuse. The cooker IF fully loaded would use just over 30A. I'm planning on adding a socket to the cooker circuit, (built into switch). I was therfore going to put the cooker onto a 40A circuit on the new CU with 6mm cabling. Does this sound OK? (Cable run from CU is fairly short and will be using kettle\toaster etc... on socket)

4) My current house supply is 60A. Should I ask to have this increased to 100A? Thinking demand will be higher after rewire due to extra cabling and lights. Or is it a case of leave it at 60A & if problems then uprate it?

5) Would you RCD protect outside light circuits? 1 x PIR Security light, 1 x Dusk-Dawn light + a few lights in outbuilding.

cheers

 

[bongos]

IIRC (from other posts i've seen on this site...)

1. Only applies to new builds. You don't have to move your socket height just because you are rewiring.

2. Cable doesn't have to be clipped AFAIK. If you were pulling a new cable betwen a partition wall I don't see how you could actually clip it to joists without taking part of the wall down to see what you were doing and get access to the joists to clip it.

3. The MCB is designed to protect the cable (although you obviously don't want one too small to avoid nuisance tripping). You can apply diversity to circuits like these as it is unlikely that you would be using the cooker on full and also the toaster/kettle altogether regularly.

4. You will have to ring your DNO to change the service fuse if you want to do this. You can also work out the max demand (applying diversity again I believe) for your house. A 60A service fuse will not blow straight away if your house exceeds 60A anyway. If your service fuse does blow then the a quick call to the DNO to replace it and they would upgrade it at that time anyway.

I'm sure someone more qualified will correct any glaring errors i've made here (not a sparky - in case you hadn't guessed )

5. Not sure under 16th edition but under 17th I don't think you have a choice (you have to RCD protect).

 

[Cremeegg]

Are you designing this to 16th or 17th?. When are the works going to be completed by the "friendly" electrician? At present dates matter.

Most DNO's will upgrade to 100A free of charge. Good time to sort out any moving of CU; moving of incoming supply; provision of isolator etc

 

[scholesy]

thanks, again really helpful replies.

Regarding point 3. My oven if fully utilised could potentially require 7.4kw which is equal to 32A ish. Now I understand you can apply diversity and that you would have to draw a fair bit mor than 32A anyway over a sustained period of time to trip the MCB, but thought with a socket added as well it may be best to use a 40A MCB. Do you think a 32A should be OK?

I'm planning to have the work done in the next few months. I was hoping the work would be OK under the 16th as i've heard the 17th has several big differences. Not sure when this comes into force though.

 

[bongos]

Planned Layout -> 1 x 40A Cooker\Socket[6mm]

You've said you're installing 6mm with a 40A MCB so you already answered it.

The MCB is there to protect the cable from overload and damage. I don't know your personal circumstances so can't say about how often you will be using the oven at full power with a high load on the socket all at the same time - you will kow the answer to that.

Also don't forget that although 6mm can take 40A when installed in certain ways, you will have to de-rate the cable if it is going through insulation etc and also take into account volt drop (although this will be minimal in the 'short run' you describe). All of this could mean that you have to decrease the size of the MCB to 32A anyway.

I think the 17th comes into force on 1st July although I understand systems designed after 1st June have to comply with the 17th (I may well be wrong )

 

[JohnD]

when you say "oven" I think you mean "cooker"

I prefer the cooker switches without sockets. Your new kitchen will surely have plenty of sockets without needing one that encourages you to drape the kettle lead across the hob.

it is also a good idea to provide a dedicated freezer circuit that is not on the same RCD as other circuits, to prevent expensive spoilage of food in the event of a trip caused by another appliance.

Have a look at your earthing arrangements as this is also a good time to get your supplier to provide a new/better one.

 

[scholesy]

thanks for the info so far, it's been very helpful.

i'm going with 32A for cooker. I'd got my diversity calcs a little wrong and seems like 32 will be OK.

Now my next hurdle has come up and again looking for some expert advice...

My current fuse box has the following layout...
[1] 30A - Cooker
[2] 30A - Ring Main
[3] 15A - Water Heater (*NOT USED - wired in with 6mm T+E)
[4] 5A - Downstairs Lights
[5] 5A - Upstairs Lights
[6] 30A - Shower (*NOT USED - wired in with 6mm T+E)

one headache I have at the moment is designing the new layout for 3 Ring Mains (Up, Down, Kitchen). When as can be seen I only currently have one and have no intentions of opening up my main Fuse Box. (remember I'm running all cables, chasing in etc.. then electrician friend will be putting in new CU).

Could I use the cables from [3]15A and [6]30A as temporary radial circuits for my 2 additional planned ring mains? I'd change the 30A fuse to a 15A. Then join the 6mm cables to juntion boxes near the fuse box and run 2.5mm T+E out to sockets. I know this is not wise (mixing cable diameters) but was hoping it may be acceptable as a short term solution.

The total cable runs are both fairly short and theirs nothing particularly demanding running on either circuit, (tv, toaster, etc...).

Thanks again

 

[Chri5]

Run a large 6 or 10mm cable for the cooker.

If you ever move towards a ceramic hob, the cable will be able to handle the load- best to do now than later.

Your works will hit 17th ed rules and so your need a CU with 2 x RCD's and a direct rail for 'other' circuits.

Other circuits would be earth leaky equipment such as (potentially) the cooker and maybe the fridge / freezer.

On 17th ed the smoke detection circuit should NOT terminate on either of the RCD rails (since it will turn off when other equipment trips) so that should terminate on an RCBO 6a on the direct rail.

 

[scholesy]

thanks for the reply Chris

I'm not sure why the smoke alarm circuit needs any form of RCD protection. Wouldn't it be OK on its own 6A circuit with an MCB? Or is it a new rule for the 17th?

cheers

 

[tim_s_uk]

I'm not sure why the smoke alarm circuit needs any form of RCD protection.

Circuits with cables buried less than 50mm must be protected by an RCD or RCBO.

 

[scholesy]

the smoke alarms should be OK then, through cavity and under floorboards. However my cooker cable is run in plastic conduit, in plaster in the wall though, (in safe zone vertical from switch). Will my cooker have to be RCD protected?

cheers

 

[ban-all-sheds]

That depends on:

1) How quickly you get started on this work

2) How happy you are to argue the toss with LABC about how much compulsion there is to comply with the latest version of BS 7671

 

[scholesy]

OK, thanks all.

I might have to buy some RCBOs from the sounds of it. Although as Ban mentioned maybe best to pull my finger out and get cracking.

Any thoughts on my plans to use the 2 existing circuits as temorary radials for Kitchen (4 sockets) and Down ring (5 sockets).

cheers

 

[tim_s_uk]

There is an overview of the changes for the 17th edition here: http://tinyurl.com/3zdtdc
Your cooker cable must have RCD protection because of the following requirement:

Cables that are buried less than 50mm into a wall or partition and are not enclosed in earthed metallic covering or have mechanical protection capable of resisting nails or screws to be protected by a 30 mA RCD.

This is just what I've found on the internet - I don't have a copy of the new regulations yet.
I would recommend RCBOs for all the circuits if you can afford it. I don't know if they are recommended for smoke alarms, emergency lighting etc.[/list]

 

[ban-all-sheds]

Your cooker cable must have RCD protection

Define "must"....