Chasing in a new cable and want to go horizontally

[WhydidIstart]

Hi, I have spent the last few hours searching the forum for answers, but as always there are plenty of regs to trip me up so it would be great if an expert could confirm if what I am planning is ok please.

I would like to add a number of extra sockets to my 1960's house and want to stay as close to the rules as possible. The problem being that when the house was rewired they only replaced the existing sockets and wiring and didn't provide any extra ones. This means that in the whole of the upstairs (hall way, large bedroom and small bedroom) there are only 2 socket outlets! If I don't add more sockets I will end up with multiple extension leads trailing all over the place which will be messy and a trip hazard.

Upstairs seems ok, I break the ring main and fit an accessible JB under the floorboards and run 2.5mmsq cable through holes in the joists until I get to the wall where I chase up to 450mm high in the wall, loop into a socket outlet and on to the next one and so on until I end up back at where I started, completing the loop.

Downstairs is harder... The floor is concrete and the walls are cavity concrete totalling 250mm from side to side. I estimate this is formed from 110mm concrete + 30mm cavity + 110mm. There is a similar lack of sockets here, the dining room having only one socket located right behind where the door opens!

I would like to sink this surface mounted box into the concrete wall and extend the ring main chasing horizontally. However this looks tricky as I can only chase 1/6 of the wall thickness (is this correct?) when going horizontally to the next socket and getting 2 x 2.5mmsq wires in an 18mm deep chase would be hard. Therefore I plan to run a single unfused spur from the existing socket in 2.5mmsq cable, but obviously can only fit one (double) outlet.

Will this be ok in terms of cable routings and not weakening the structure of the building too much?

Finally just out of interest, I believe I can replace existing damaged cables and outlets (on a like for like basis) even in a kitchen without requiring Part P certs, etc. Also a previous resident could legally have installed extra sockets in a kitchen in December 2004. If all their cabling became damaged this year, could I then legally replace all the cables for new harmonised cables and outlets? This would then look remarkably like a new install in a kitchen, but be totally compliant with the Part P regs?

 

[bremen1874]

Here's my semi-informed opinion...

Fitting junction boxes under floorboards isn't allowed. You either need to start and end at an existing outlet or make the join the join with heatshrink covered crimps.

I can't see a problem getting two 2.5mm T&E cables into an 18mm deep chase, just make the chase wide enough to lay the cables side by side.

I believe that Part P allows you to replace face plates on a like for like basis and replace a single cable due to damage. What you're talking about is far more major and I'm sure would be covered by Part P. If you want to make up stories to justify ignoring building regs then that's up to you.

 

[securespark]

Bite the bullet & notify.

BTW, you don't need 450mm unless a refurb.

 

[BS3036]

I have taken the 1/6 wall thickness rule to mean the original wall (building block). Presumably there's another 20mm of plaster on top which you can also remove?

 

[JohnD]

If you want to add more sockets on a ring you may be able to do it with this method, which is extremely useful in rooms with just one socket in them, or in kitchens, offices or workrooms where you need a lot of outlets in a row above the worktop:

Take out an existing socket. It will have two "legs" of the ring going into it. Fit a "Dual Box" which enables you to mount two single sockets together.

connect one leg to the Right-hand socket and one leg to the left-hand socket

Connect a new cable to the right-hand socket

Run it horizontally around the room, adding new sockets at intervals. When it has circumnavigated the entire room, connect it to the left-hand socket.

You can see that doorways will be an obstruction. One way to get past them is to put a socket on each side of the doorway, and run downwards from them, putting the cable under the floor. This is more difficult with a concrete floor

You do not actually have to run the cable all the way round the room if you don't want to, you can run it back using the same route. It is a great advantage to run the cable in oval plastic conduit, this makes it easier to cut a new socket into the route later. However, the cable leaving the righthand socket must return to the left-hand socket after completing its loop. Do not connect the left-hand and right-hand sockets directly.

The addition of more sockets on an existing circuit is not notifiable, except in a kitchen

 

[nozspark]

If you are going to do just a single run (to one side of) of many sockets off the existing socket then you really should alternate the order in which the sockets are fed.

EG. if you do what John says, just label the cables a&b.
Cable 'a' feeds socket 1,3,5 & 7
Cable 'b' feeds socket 2,5 & connects to socket 7 to complete the ring

 

[JohnD]

good idea.

the "return" leg often goes through the socket boxes, which is OK until you need to take one out but if it is broken at the sockets on either side, and run in oval conduit, that makes it an easy job.

 

[Cremeegg]

Those Regs that trip you up are there for a reason - are you sure that your existing installation can cope with the additional wiring. Is your 60's cable OK? - I've seen some pretty ropey 1963 vintage PVC cable recently that came very close to failing its IR tests - so I replaced it anyway.

 

[luminaire]

Have you thought of using trunking instead of having to chase.
have a look at this for a change or even this

 

[WhydidIstart]

Wow, a great response thanks for all your comments.

I’m not sure if the wall thickness includes the plaster, but don’t feel comfortable making a deep chase horizontally all round the room. The plaster is also less than 20mm, probably only about 10-15mm, but I could probably make a 20mm chase that only goes slightly into the concrete. A good point that I hadn’t considered.

I also really like the ‘dual box’ idea from John and the tip from nozspark of alternating the sockets if only going one way from a socket. I will see if the cables already fitted have any movement as I could always mount two double sockets next to each other as 4 sockets would be quite handy where the existing one is currently located.

To get round the concrete floor issue, can I run the chase round the door frame then back down and continue at the same level as before to create a new loop?

Crememegg (nice name btw ) the original 60’s wiring was rubber insulated single and twin core run through metal conduit, must have been some of the last rubber fitted, but luckily for me the house was rewired in the mid 80s (estimate) with modern PVC cables. All the light fittings now have Earths and all the cables I have uncovered look fine. The old rubber ones and junction boxes can still be seen in the loft and under floorboards, but are all dead and mostly chopped out.

Luminaire – I have seen trunking similar to the 2nd link and didn’t think it would really look right in the house + would be expensive. However the first link has got me thinking as they show it on the floor. I am going to put laminate flooring down and this requires a trim to be fitted between the skirting and floor to cover the expansion gap. If cables could be run in a plastic version of this it would probably look ok. The site only shows it being used with phone and A/V cables, do you know if the regulations would allow it to be used with T&E – I guess it does provide mechanical protection… I’m not sure how easy it would be to go through the skirting to get the wires to the socket on the wall though. Any ideas?

Finally

Fitting junction boxes under floorboards isn't allowed. You either need to start and end at an existing outlet or make the join the join with heatshrink covered crimps.

Are you sure this is correct? I don’t know any better, but I’ve never seen heatshrink on a ring circuit, or any proper house wiring to be honest and have also seen plenty of JBs used for lighting circuits fitted under floorboards. Do the rules regarding JBs and their location differ for lighting and ring circuits?

Thanks.

 

[JohnD]

you can go up and over a doorframe.

however, you need to run the cable in "safe zones".

The idea is that if you have a sudden desire to drill a hole or drive a nail into a wall, and you see an electrical socket there, you can reasonably expect that the cable will go directly up, or down, or sideways from it. You can then investigate to see if your hole is safe.

So, if you put a socket to each side of the doorway, running the cable into it from the next sockets on the wall, the horizontal cable is in a safe zone. You can then run the cable vertically upwards. You will probably not want a socket above the doorframe, but another safe zone is within 150mm of the junction between the wall and the ceiling' so you can run along there, then vertically down to the other socket.

If you don't mind, or you have a high-level extractor fan or IR heater, you can put an FCU or other outlet where the cable turns down, or even a blanked-off box which has a square white plastic cover. this will make it easier to change or repair cables in future, and also makes the cable run more obvious.