Complete DIY Rewire - Including CU

[SkyVanMan]

Hi All,

Been lurking for a few days and having a little mooch about the forums and decided to register and post for comments and advice.

I've looked around various forums and this seems the most varied and also the most sensible and the place where I am least likely to get shot for asking questions about a DIY rewire.

Now this is going to be a relatively long post so my apologies in advance but I hope there are a few people around who manage to make it to the end and provide any comments or advice they see fit - both positive and negative.

My Dad has just bought a relatively small house which is need of gutting and a complete refurb. In order to save some money I will be doing various things for him, one of which is the rewire and replacement of the consumer unit.

I'd also like to clear one thing up from the beginning. The entire refurb, including the rewire and Consumer Unit replacement will be notified to the LABC. In fact, he may already have sent the forms off this week. He is dealing with the notification and any associated paperwork, I am simply doing various jobs that I know I can do. I'm posing this rather lengthy post to see what opinions, comments and advice people have in order to avoid any mistakes which would require rectification prior to approval by the council.

Now, to the point of the post. Basically, the entire house will be rewired. The house consists of a living room, a kitchen / dining room, stairs and small landing and two decent sized bedrooms. Oh, there's a bathroom too obviously!

I'm going to leave the existing installation in for the time being so there is power to the house until "switchover day". The existing CU is of the removable rewirable fuse type with 6 ways. The installation is not RCD protected in any way. There is also an electric shower in the bathroom. Now I may be wrong but I though any electric shower had to be RCD protected. If I'm correct then I have no idea when this reg was introduced but this is a fairly recent looking shower installation (within last four years or so I'd say).

So anyway, I'm planning on fitting a MK 12 way Dual RCD CU which should provide plenty of capacity for future extension. It will have a 100A main switch with a 80a and 63a RCD's.

I'm planning separate circuits for:

32a 2.5mm Kitchen ring (& an IP56 outdoor socket)
16a 2.5mm Radial for appliances (but thinking a 32a ring would be more sensible)
32a 2.5mm Living Room ring (basically a downstairs circuit minus the kitchen / dining room)
32a 2.5mm Upstairs ring
6a 1mm Downstairs Lights
6a 1mm Upstairs Lights
40a 10mm Shower

Consumer Unit will be located in the living room and the cables for the downstairs circuits will be taken straight down into the crawl space and then will rise to each outlet, buried in plaster. Cables for the upstairs circuit, both lighting circuits and the shower will go straight up the wall from the CU, buried in plaster, and will then go around the house in the void between ceiling and floor (except the upstairs light circuit which will obviously continue up in to the loft).

Am I right in thinking that I am allowed to run the cables straight up the wall in the safe zone that is 150mm from the corner? I was thinking about boxing the cables in anyway with plasterboard rather than burying in bonding for future access. The consumer unit will be located in this corner too so does the safe zone extend to the area vertically above the consumer unit? However, the CU will be in a cupboard so it may not be immediately apparent that this is a safe zone.

Now the upstairs and downstairs rings and lights are straightforward. There will be a relatively large number of sockets on each ring to provide greater flexibility in the future but this isn't an issue as far as I'm aware.

As far as the kitchen ring goes, this again is straightforward with the exception of the outside socket. The entire installation will be RCD protected but are there any other issues I need to be aware of when it comes to installing an outside socket? The cable feeding the socket will basically come straight through the wall from behind the IP5 socket. There will be a switched FCU inside which will allow the power to the outside socket to be cut when my Dad goes away and stuff.

For the shower, is a 40a MCB and 10mm cable over a run of not more than 15m sufficient for a 10kw shower? The shower cable will be clipped direct to the inside of an external wall for about 2.5m and either buried in plaster or covered by plasterboard in a small 1" cavity. From there it will be in the void between ceiling and floor before it rises in the all to an isolator switch outside the bathroom. It will then rise again from the isolator switch to the loft, across the loft a little and then down the wall to the shower. This time, where the cable is in the wall by the bathroom it will be clipped and buried in bonding. Is there any need to enclose it in capping other than for ease of access in the future? Maybe a 45a MCB would be better as based upon a 240v supply 10kw is rated at 41a and based on a 230v supply slightly higher at 43a or thereabouts.

In terms of the layout for the CU, I was thinking of having the downstairs ring and the kitchen ring on the 63a RCD, the upstairs ring and the shower on the 80a RCD, the lights on their own 6a RCBO's and the Appliance radial or ring on it's own 16a or 32a RCBO too. Thinking about it, maybe I'd be better off putting the outside socket on the appliance radial / ring.

My Dad also wants provision for a supply out to the shed a the end of the garden. I'm not too sure about how to go about this just yet so will need to research some more. I know I'll need SWA cable and it needs to be buried a certain distance below ground but I don't know much about connecting it to one of the circuits or if this is even allowed.

Oh, another thing, I was thinking of fitting an emergency light on the stairs. Does this seem a bit overkill? I just figure it's prudent and may as well be done while the whole install is being done. Any recommendations as to a non too ugly, reasonably priced emergency light? Also, what's the difference between maintained and non-maintained (I know the clue is in the name lol but what maintenance is required?)

Oh yeah, another question . Sorry. When I'm running cables under the ground floor I was just planning on clipping them along the underside of the joists. What do I do though when clipping them across joists? I know cable trays would be preferable but they're expensive and I also can't be bothered with the hassle of fitting them if they're not entirely necessary. Can I just clip to on joist, run cable to the next with a small amount of slack and then clip to the next?

For running the cables under the floor upstairs I'm going to drill the joists (and forget about any notching that already exists - I won't be re-using notching) where cables need to pass across joists. I know there are regs regarding drilling joists so I'll need to refresh myself on them but I recall that holes must be a minimum of 50mm from the surface of the joist and must also be a certain distance from the end of the joist and also a certain distance from other holes. I don't think the hole diameter can exceed a certain percentage of the depth of the joist either. I won't be using one hole for all cables - the most will be one 10mm cable through a 16mm hole or one 2.5mm cable and one 1mm cable through a 10mm hole. Is that acceptable?

I think that's it for now. I'm sure there'll be other questions but I'll post if I think of any others.

Oh yes, there is another one. Building regs state sockets must be no lower than 450mm off the floor and light switches no higher than 1200mm of the floor. Now as this is a complete refurb I assume these regs apply to my Dad? He's not too happy about having them at this height but regs are regs and if they apply then it won't be signed off unless the installation complies. A daft question on this though. For sockets, is it the BOTTOM of the socket that can't be lower than 450mm and for switches is it the TOP of the switch that can't be higher than 1200mm.

And another point! I obviously don't own the equipment to test the installation. From what I can make out, the council don't go as far as testing the installation, they only ensure it complies with the regs. Once installed, would getting a PIR done be a good idea?

Ahh, and another, bonding. From what I can make out on the regs, main and equipotential bonding isn't necessary now. However, is it still worthwhile? Gas box is within a couple of feet of the CU anyway and it's no hassle to run a cable to the water stopcock. Would it be 10mm earth cable I'd need to use?

Right, that really is it for now. Apologies for the mega long post and thanks in advance for taking the time to read this assuming you managed to stay awake and got this far.

SkyVanMan

P.S. Not sure if the supply is TN-s or TNC-s but I know it's definitely not a TT supply. Any pointers on how to determine the type of supply?

 

[rebuke]

Answering some of your questions (it would have been helpful if you'd numbered them )

Have you thought about using all RCBOs rather than dual RCD - it will be slightly more expensive, but is the 'better' solution?

Circuit wise - what you do mean by appliances - isn't that what your 32A kitchen ring is for?
Is there an electric oven / hob - as this will probably need it's own circuit if so (and even if there isn't, if there is the potential for it in the future it might be worth putting a circuit in now while you're chasing lots of walls etc anyway)?

Boxing the cables in would probably be nicer than just running lots of cables up inside the wall (which might be tricky anyway given the size of the chase you would need). You could put in a bit of e.g. plastic maxi-trunking rather than plasterboard, depending on where and what it needs to look like etc. For reference though yes there would be a safe zone immediately above,below and to the sides of the CU.

With rings you just need to make sure the total area covered is not >100 square metres.

For the shower, is the cable under any insulation in the loft, as this affects the rating of the cable.

Personally I'd put the outdoor socket on it's own dedicated RCBO, that way if it trips due to water ingress or similar, you don't lose anything else.

As for shed it would be best to run it as a sub-main, so you have a dedicated circuit in the CU for it (if you're using SWA, you don't need to RCD protect the cable, so you could use an MCB in the CU, then have e.g. an RCD main switch CU in the shed). This obviously depends on what you want to run in the shed though...

Emergency light sounds like a good idea - just bare in mind that there aren't many that look 'suitable' in a house setting, make sure your dad likes it!

Given it's a rewire rather than a new build, you could probably argue part M (i think it's M, might be wrong) doesn't apply so you don't need to use the new heights, but as you say it might be tricky to get the LABC to agree to it.

It is the LABC's responsibility to inspect and test as they see necessary, most just subcontract an electrician to come out and effectively do a PIR, but if they don't then I would definitely get an electrician out yourself!

Main bonding is absolutely still necessary - you need to use 10mm cable from the MET (main earth terminal).

As for TN-S vs TN-C-S, where is your main earth taken from, if there is an earth cable coming out the cut-out, that normally indicates TN-C-S, if there is only something coming from the sheath of the supply cable, that's probably TN-S (but post a pic of the various things and people here will tell you).


Other things to think about:
Do you want mains powered smoke alarms (they're not expensive, and easy enough to put in)?
I would suggest you at least buy a copy of the on site guide (amazon among other places stock it). It gives you the tables you need to work out cable sizes, and details of the important regs that apply. It would also be worth investigating test kit, I got a full set for about £60 off ebay, which is useful (even if the LABC are going to test it, it's nice to be able to do tests yourself before energising it).

 

[rebuke]

Other thing to mention with bonding, is supplementary bonding is not required in bathrooms under the 17th assuming that all circuits are protected by at 30mA RCD, and that any exposed metalwork (pipes etc) has a sufficient connection back to the MET (can't remember exactly what resistance the regs state, don't have them in front of me)...

 

[SkyVanMan]

WOW! Thanks for the quick and detailed reply.

Cooker - well spotted. I meant to mention it. My Dad is just opting for a gas cooker. however, I have said to him that we should pre-wire it for an electric oven for future use. He's only planning on staying there for a couple of years because his work will probably move to another area so I've suggested we install a 10mm cable to the kitchen and terminate it at a cooker outlet isolator thing above worktop and at a cooker outlet thing below and to the side of where a built in oven would go. That way it leaves an option for a double electric oven in the future. I could also run an additional one I guess to potentially power an electric hob but given there's a gas supply there anyone buying in the future will just have to make do with a gas hob.

OK, so main bonding IS required. I read that bit wrong. Thanks for the clarification. So it's only suplementary bonding that's not. I guess there's no harm in supp bonding though anyway?

Will have a look at where the earth supply comes from when I'm over there tomorrow.

For the kitchen appliances, I was thinking a separate circuit for the fridge and freezer on its own RCBO. I had thought about washing machine and dishwasher too but they can go on the kitchen ring with switched FCU's above worktop. For the fridge and freezer I figured their own circuit so that if anything else trips the RCD they on't be affected. I think a 2.5mm radial and just a 16a RCBO will suffice if there's no washer or dryer on the circuit.

For the ourdoor socket, I think I'll take your advice and put it on its own circuit with an RCBO. For the shed, I don't think he's wanting to run any powerful lights or anything like that for growing stuff he shouldn't lol, I think it's just for tools and the mower etc. Is a dedicated garage CU required or could I have the outside socket and shed on their own 16a RCBO directly from the CU. I'm thinking maybe, 2.5mm cable from the CU, through to the back of the house into the outdoor socket. Then from there, back into the house in the crawl space, connect to 2.5mm SWA cable and then out to the shed. Is there such a thing as a connector to join standard cable and SWA cable? That would reduce the amount of SWA required by about 12m.

I'd considered using all RCBO's but it does work out considerably more costly. OK, so he's saving over £2,000 because I'm doing the work for him but even still, he wants to keep the costs down as much as possible so the money can be spent in other areas.

For the boxing in, the CU will actually be located in an alcove type recess so I was just thinking of running a couple of battens up either side of the recess and then screwing plasterboard to the battens. Job done. OK, so the cables are effectively sealed in and damage may be necessary in the case of future access but I could lay a couple of bits of wire to pull cables through in the future if necessary.

The shower cable won't be buried in any insulation. I'm planning on taking it into the loft space and then clipping it along a joist and then fixing a spacer joist of sorts to the side of it prior to the loft insulation going in (which we'll be doing ourselves) so it's not covered and has a bit of ai around it. I was planning on having the shower isolator outside the bathroom door. Is that OK or does it have to be a pull switch inside the bathroom?

Re the 17th Edition on site guide. I got myself one at borders last week and have been engrossed all weekend. Most of it may as well have been Greek but I have taken a lot in so far and I'm sure I'll take a lot more in over the next couple of weeks. Tomorrow and Thursday I'll be chasing out and sinking back boxes, planning cable routes etc. Then the back end of next week I'll be laying cables. After that we're relying on the council inspector before I can plaster over the chases and cover up the work (along with then ripping out the exisiting installation and filling in all the socket and switch recesses etc). At this point there'll simply be two double sockets necxt to the current CU.

Once that's done the whole place will be skimmed, dried and decorated before then connecting all of the face plates and switches etc and putting the new CU in and connecting it all up.

I'm not sure what happens then though. I don't know if I'm allowed to energise it or if I then have to wait for the council to inspect second fix before it's made live.

Slightly nervous about covering it all up and having plasterers in before checking it's working fully but hey, it's a risk I'm going to take. If there are any mistakes they won't be due to forgetting to lay a cable to a particular socket.

Thanks again for your reply.

 

[rebuke]

Absolutely no harm in putting in supplementary bonding, in fact it may even be required if any of the new plumbing that's presumably going in (given you said the house is being gutted) involves sections of plastic pipe, since there won't necessarily be continuity back to the MET at that point...

If you're putting in a separate thing for the fridge/freezer - run it in something like ali-tube, then you don't need to RCD protect it (just make sure the socket is labelled as fridge/freezer only), that way even less danger of it tripping out. You'd probably get away with 1.5mm for a 16A circuit (depending on installation factors), but no harm in using 2.5mm.

If you just want a socket and light in the shed, then you don't need a CU, it just gives more flexibility should you want to do anything in the future. Putting it on same circuit as outdoor socket would be fine. As for joining it - the normal way is to use an SWA gland on some sort of box - I suspect you could put an SWA gland out the bottom of your outdoor socket, straight down and in to the ground.

 

[comms]

Ringmain for the kitchen including appliances (32amp)
Radial 10mm cooker circuit.
Downstairs sockets (as radial circuit(s))
Upstairs sockets (again a radial circuit(s)
Lighting down
Lighting up
Lighting outside
Immersion tank supply (radial)
Main equipotential bonding to gas & water services.
Smoke detectors (interlinked) circuit on their own rcbo.

Holes in joists
- Should only be drilled on the centre line of the joist.
- Should have a diameter no greater than 0.25 times
the depth of the joist.
- Should be no closer together than 3 times the larger
diameter.
- Should be no closer to the support than 0.25 times
the span and no further away than 0.4 times the span.

And just for you a nifty little link (but it is in the osg) showing the above.
http://www.wycombe.gov.uk/uploads/d...ning/LocationofNotchesandHolesinJoistsA04.pdf


And a word of warning.
If you are leaving the old installation in situ & energised, while you chase the new installation in, be aware of old cable runs (they dont always go where you expect them to go)

 

[ColJack]

you enquired about energency lighting?

maintained means always on, non maintained means only comes on when the power goes off..
you can also get switched maintained which as it sugests acts like a normal light but has built in emergency backup..

I'll have a hunt for you but I'm sure you can get conversion kits to turn regular lights into emergency ones.

hob needs to have a 10mm to it, double oven will be ok with a 2.5mm 20A supply normally.. ( most are in the region of 16A.. )

appliance radial / ring:-
ring would be better, a washing machine going full out will be close to the 13A of the fuse, which on a 20A radial only leaves you 7A for the dishwasher / tumble dryer etc.
use only single socket outlets for the appliances.. doubles quite often don't like 2 heavy current items in them..
use FCU's above the counter and unswitched sockets below.

I don't like the idea of using cable tray under a suspended floor.. gives ratty somewhere to sit while he gnaws your cables.. much harder to do whilst hanging by his claws from a joist..

while you've the floor up, might be a good time to think about central heating? if you have it already, get the pipes checked, if not get them fitted even if you're not putting it in now.. it's much easier than getting all the carpets up again..

 

[SkyVanMan]

If you're putting in a separate thing for the fridge/freezer - run it in something like ali-tube, then you don't need to RCD protect it (just make sure the socket is labelled as fridge/freezer only), that way even less danger of it tripping out. You'd probably get away with 1.5mm for a 16A circuit (depending on installation factors), but no harm in using 2.5mm.

Thanks for the aditional reply rebuke.

I'd thought of burying it deeper than 50mm but decided I couldn't be bothered. Forgive the question but what's ali-tube? It's a decent idea not to RCD the fridge and freezer if it's possible. Another thought. The cable for the fridge and freezer will be coming out of the CU and will be going straight down, unconcealed (because there will be a cupboard around the CU), then through the floorboards and along the crawl space, then up behin the fridge and freezer. Now aesthetics aren't important in the area where the fridge and freezer will be so what if the cable was just surface mounted, say in a bit of conduit? Would that then negate the nee for RCD protection on that circuit?

If you just want a socket and light in the shed, then you don't need a CU, it just gives more flexibility should you want to do anything in the future. Putting it on same circuit as outdoor socket would be fine. As for joining it - the normal way is to use an SWA gland on some sort of box - I suspect you could put an SWA gland out the bottom of your outdoor socket, straight down and in to the ground.

An SWA gland. Thanks. I've had a look at one on tinterweb and they look complicated. I'll get one and have a little play about with it - I'm sure they're self explanitory. I've got the IP56 socket - was delivered today to my home with several other items (the weight of all the cable almost finished the courrier!) and there isn't a knockout at the back of it. Only one at the top and two at the bottom. I think I'm going to have to use a bit of circular conduit tube stuff and elbow things because the cable will have to exit through the wall and then go up to the socket. DOn't really want exposed PVC cable no matter how short so will have to look into solutions to that.

Thanks again for your help.

 

[rebuke]

Ali-tube is a type of cable that is protected by (as I understand it, never actually used it myself) a metal wrap. The regs allow it therefore to be used withotu RCD protection when buried in walls.

Surface mounted (either clipped direct) or in conduit would negate the need for RCD protection, so that's also an option (again though make sure the socket is labelled as being only for the fridge/freezer, since general purpose sockets must be protected).

There's a guide on the diynot wiki as to how to terminate SWA (//www.diynot.com/wiki/electrics:swa-gland) - it's a bit fiddly, but not too difficult.

You could make a hole in the back of the socket, just make sure it doesn't end up a route for water to get in (another tip a number of people suggest is to drill a small drain hole at the bottom of the socket, so any water that does manage to get in can find its way out).

 

[SkyVanMan]

Ringmain for the kitchen including appliances (32amp)
Radial 10mm cooker circuit.
Downstairs sockets (as radial circuit(s))
Upstairs sockets (again a radial circuit(s)
Lighting down
Lighting up
Lighting outside
Immersion tank supply (radial)
Main equipotential bonding to gas & water services.
Smoke detectors (interlinked) circuit on their own rcbo.)

Cheers comms.

Ofcourse - I didn't even think about an outside light. As there'll only be one security light outside it doesn't seem worth having an entirely separate circuit for it. Would it make sense to just run this security light on a switched FCU off the outside socket and shed socket circuit?

Also forgot about boiler. There's no immersion heater but there is a combi boiler. Does the combi boiler require its own circuit or can it just be run off an FCU on the kitchen circuit.

Holes in joists
- Should only be drilled on the centre line of the joist.
- Should have a diameter no greater than 0.25 times
the depth of the joist.
- Should be no closer together than 3 times the larger
diameter.
- Should be no closer to the support than 0.25 times
the span and no further away than 0.4 times the span.

And just for you a nifty little link (but it is in the osg) showing the above.
http://www.wycombe.gov.uk/uploads/d...tionofNotchesandHolesinJoistsA04.pdf)[/QUOTE]

Thank you. I've seen it somewhere but just couldn't remember what the exact details were. I'll find the page tonight so I've got it to refer to tomorrow.

And a word of warning.
If you are leaving the old installation in situ & energised, while you chase the new installation in, be aware of old cable runs (they dont always go where you expect them to go)

LOL, my house was like that originally. Cables everywhere, the greatest being the cooker cable which went diagonally up the wall!

 

[SkyVanMan]

you enquired about energency lighting?

maintained means always on, non maintained means only comes on when the power goes off..
you can also get switched maintained which as it sugests acts like a normal light but has built in emergency backup..

I'll have a hunt for you but I'm sure you can get conversion kits to turn regular lights into emergency ones.

hob needs to have a 10mm to it, double oven will be ok with a 2.5mm 20A supply normally.. ( most are in the region of 16A.. )

appliance radial / ring:-
ring would be better, a washing machine going full out will be close to the 13A of the fuse, which on a 20A radial only leaves you 7A for the dishwasher / tumble dryer etc.
use only single socket outlets for the appliances.. doubles quite often don't like 2 heavy current items in them..
use FCU's above the counter and unswitched sockets below.

I don't like the idea of using cable tray under a suspended floor.. gives ratty somewhere to sit while he gnaws your cables.. much harder to do whilst hanging by his claws from a joist..

while you've the floor up, might be a good time to think about central heating? if you have it already, get the pipes checked, if not get them fitted even if you're not putting it in now.. it's much easier than getting all the carpets up again..

Thank you coljack. The explanation of maintained / non maintained helps a lot. Now I know what I'm looking for and will also google conversion kits.

I was planning on sockets below, FCU's above but was going to use doubles. I'll use singles - thanks.

Thanks for the info on cable trays too. At least I can now justify this to myself for not using them now. I'm not cutting corners, I'm being prudent lol.

Re the central heating. Unfortunately the only thing in the house that is fairly recent is the central heating system. Probably less than 2 years old so it's being left alone (although I'll be dropping the radiators before the plasterers arrive).

I say unfortunately because if it wasn't so recent I'd be ripping the whole lot out and putting in plastic, buried in the wall and coming out behind the radiator so all pipework is concealed and radiators effectively float on the wall like I did in my own house. I know the odd pipe rising from the floor to the radiator isn't exactly an eyesore but I just like as much concealed as possible.

 

[SkyVanMan]

Well, the first day went well (ish). I managed to get about three quarters of the back boxes fitted and a bit of the chasing work one. Also discovered that the crawl space beneath the house is pretty deep too. Starts off at about 5 feet deep and then gets shallower towards the back of the house - but still has about 2.5 feet of space at the back so that's going to make cable routing for the ground floor a bit less uncomfortable.

I found a bit of dry rot down there though so my ad's not the happiest guy around at the moment but it only looks like a small contained area and can be easily and cheaply resolved.

I think it's a TN-S supply based upon rebuke's explanation. There is a 10mm earth cable clamped to the sheath of the big fat supply cable.

 

[ColJack]

forgot to suggest..

fit an emergency light above the CU.. it's easier than trying to find a torch if the lights go out in the night..

 

[17thman]

I think you will find mains interlinked smoke alarms with battery back up in the circulation spaces on both floors are necessary with a rewire. fit not less than 300mm from a wall and not near(dont recall measurement) a light fitting and not over a stairwell.

As long as the building is not left in a worse state of compliance with part m you are ok.

When in loft, dont drill or notch the ceiling joists.

Make sure that the cable entries into the top of the cu, if that is the entry point are IPx4 or less,

Grommets in back boxes.

25% of light fittings need to be low energy pendants.

Good luck.

 

[securespark]

Not just pendants, surely?

You can use (for example) 2D and fluorescent fittings.

But these rules apply just to refurbs.