Concrete flat rewire!

[petearm]

Hello all,

My girlfriend and I have clawed our way onto the property ladder by buying a 1 bed flat. It's all concrete and the ring mains and lighting circuits are run through conduit. The wiring is pretty haphazard throughout with one spur running through the plaster with no earth ! We also need to install heating and want an economy 7 system with fan assisted storage heaters. For the above reasons we have decided to get the place rewired.

I've had several electricians come round to quote, the general consensus was that the existing conduit would be a nightmare to use. After listening to various schemes I think we've decided on running most of the wires through "conduit coving":

http://www.interplast.co.uk/pubcontent.asp?subcatID=193

We'd then run vertical chases down to the sockets and light fittings. The remaining problem however is getting along the ceiling to the light pendant (I think a ceiling light is preferable to wall lights). Two of the electricians suggested chasing along the ceiling but I really don't want to do this as it could create a stress concentration and compromise the structure. There is the nuclear "false ceiling option" but I'd rather avoid this route since I don't want to reduce the ceiling height. If this option remains on the table I was wondering if we could simply rawplug another layer of plasterboard throughout on the ceiling and chase into the two layers to provide sufficient depth?

The other idea is to use trunking along the ceiling, I've noticed a few low profile conduits on the market such as d-line:

http://www.d-line.co.uk/

I'd cut this into the conduit coving and run to the pendant. With the profile being semi circular it shouldn't cast so much of a shadow. The problem with this is that I'm worried it will look naff and put off people who may want to buy the flat in future. Has anyone any experience of going this route?

Cheers

Pete

 

[flameport]

I've had several electricians come round to quote, the general consensus was that the existing conduit would be a nightmare to use

Did they actually examine the conduits, or did they just assume it would be too difficult? Or had they never worked with conduit before?

Unless the conduit has corroded or fallen apart (both very unlikely), can't see why it couldn't be reused.

 

[petearm]

They had a look at the conduit which currently has single wires run through it and they weren't confident in running new cable through without it jamming on the tight bends.

I am tempted to buy some 1.5mm cable and attempt to run it through the conduit myself to see what happens...

 

[flameport]

they weren't confident in running new cable through without it jamming on the tight bends.

Get another electrician then - the wires won't jam because there won't be any tight bends.

Consider that when the conduit was first installed, whoever did the original wiring had to pull the wires through it, so if it was possible then, it is possible now. Plus you have the added benefit of being able to use the old wires to draw in the new ones.

 

[holmslaw]

..

 

[bernardgreen]

Sorry flameport but my experience has been been that getting 2.5mm twin and "earth" through old conduit can be extremely difficult and can end up with unseen damage to the cable where it is pulled around elbows in the conduit. Even geting the old singles out can be impossible if the conduit has a "S" bend in it.


Some of those conduit in concrete installations were wired up as a loom with the conduit joints open. Then the conduit joints were closed up and the conduit put in place, a ready wired loom, and the concrete poured over it.

 

[petearm]

The surveyor estimated that the flat had been built in 1965.

Bernardgreen, we would only be using the conduit for 1.5mm cable for the lighting circuits and conduit for the power rings (since existing conduit doesn't seem to go all the way round the rooms since it was only ever intended for a single socket and light per room being a 60s flat...)

Would it be worth me trying to pull the old cables out and draw a chord after them to establish whether the conduit route is worth a try?

 

[dingodeano]

Just looked at a similar job. However this one was all done in pyro embedded in concrete. the pots for the sockets are all clamped to the rear of galv boxes on sockets and switches.
The IR reading is less than 1.3M between Live and Earth on the lighting circuit.
Client has decided on wall lights as alt to having surface trunking in center of rooms.
Dont want to hijack this thread but anyone know what is the life span of mineral cable ? As i may suggest as a long term investment repalacing all the wiring however the rest of the installation tests were 'acceptable'.

 

[flameport]

Sorry flameport but my experience has been been that getting 2.5mm twin and "earth" through old conduit can be extremely difficult

Hardly surprising - who in their right mind would try to pull T&E through a conduit?

 

[bernardgreen]

For the ceilings run 25mm thick by 50mm wide battens across the ceiling screwed to the ceiling. Spaced at 400mm to suit the width of plaster board, ask a plasterer for advice on the exact postioning. Put all your cables in place tacked to the ceiling with strong double sided tape or clipped to ceiling if pins will stay in the concrete. Leave a gap in battens where cables would other wise cross them. Make a note of where these cables are so you know where they are when hidden by plaster board. Then screw the plaster board to the battens avoiding places where there are cables. The cables being between the plaster board and the ceiling will need RCD protection.

You might be able to use thinner battens depending on the size of cables you need to run if you are running power cables as well as lighting cables.

But check this is compliant in the opinion of the Building Control officer overseeing the work. They will need to be involved as I assume you will be re-wiring in kitchen and / or bathroom as well.

 

[bernardgreen]

Sorry flameport but my experience has been been that getting 2.5mm twin and "earth" through old conduit can be extremely difficult

Hardly surprising - who in their right mind would try to pull T&E through a conduit?

I could name and shame the person. Though I suspect he is long since retired. The 2.5 was a loose fit at the ends of the conduit so it seemed it would work.

 

[holmslaw]

..

 

[petearm]

Just spoke to someone who sells cables, he reckons that it is sometimes possible (if the plaster is deep enough) to simply chase to the concrete without disturbing it then put in the 1.5mm T&E before capping and skimming... my concern would be that there would be insufficient thickness of plaster making it brittle and prone to falling out or this would contravene regs about how deep a chase has to be?

 

[holmslaw]

..

 

[ban-all-sheds]

Have you thought about dot'n'dabbing the walls to give you somewhere to run cables?