Concrete ceiling - wiring new lighting circuit

[benjiman]

Hi all,

Got a ground floor flat with concrete ceilings. The current wiring is done using some kind of cabling Ive not come across before. (See pic) 2 core, live and neutral, no earth.

So assuming this will fail to pass an eicr as it stands.

The cable it appears has been cast into the concrete during the build.

What are options for concealing the cable for the rewire? Conduit stuck to the ceiling will really spoil the look of the place and will be an eyesore.

Dropping the ceiling involves a lot of work with studding out and plasterboard.

What are thoughts on chasing cable within the ceiling? Any safe way to do this?

Thanks.

 

[EFLImpudence]

No picture visible. Just copy and paste.

 

[benjiman]

Sorry forgot to attach image. Here it is.

 

[333rocky333]

I dont think its a good idea structually to chase out more of the main ceiling, maybe into what looks like rendering.
Could you reuse the chase what is there, i assume that was safe

 

[Robin0577]

The current wiring is done using some kind of cabling Ive not come across before. (See pic) 2 core, live and neutral, no earth.


Thanks.

That looks like mineral insulated cable aka MICC or "Pyro"

The outer copper tube is the earth. However, the section shown in the photo is now useless as it requires special glands and tools to terminate it and seal the ends, and if the end is left open like that, the insulation will absorb moisture from the air. If installed properly, left alone and not physically damaged, MICC cable will outlast virtually any other type of wiring, it could easily last a century. It is still available, but it's very expensive both in material cost and labour to install. Relatively few modern electricians have the skills and tools to do it.

https://www.edwardes.co.uk/products...-pvc-covered-light-duty-micc-cable-per-metre-

Edit to add: If the rest of it is undisturbed, there's a good chance it will pass an EICR once that damaged section in the photo is replaced.

 

[sparkwright]

Is that pyro?

If it IS pyro, then it lasts virtually forever, and the sheath is the earth.

However, cutting it or removing the pot introduces damp into the mineral insulation - which is NOT good.

 

[Harry Bloomfield]

Is that pyro?

If it IS pyro, then it lasts virtually forever, and the sheath is the earth.

However, cutting it or removing the pot introduces damp into the mineral insulation - which is NOT good.

Yep, 'Pyro' why the end not sealed/ open to atmosphere. Depending on how long it has been open like that, it might be possible to dry it out and fit a new seal. The technique involves making a judgment as to how far the moisture has progressed, then heating the cable up from further back than that point, slowly moving the heat source towards the open end to drive the moisture back out.

Sealing the end then needs special tools and some experience. The modern replacement is FP cable, which I just happen to have some surplus stock of here, which is much easier to use than Pyro. The photo looks as if the Pyro has been set on the surface, then plastered over, in which case it should be removable to enable it to be replaced with new, then plastered over.

 

[benjiman]

Thanks for the replies guys.

That section of the cable was wrapped in isulation tape and its actually a picture of it on a wall before going off into a juction box.

Its still in one piece, not sure what happened at that point but they seem to have stripped it of the outter copper sheath then change of mind? And sealed it back up.

Anyways have discovered that on the ceilings the same cable has been used. It goes drom the switch back box to the middle of the room in a diagnal run to the rose!

It has been plastered over, held in place in sections by two galvantized clout nails.

Can it replaced with 1.5mm using the same concealement method? Ie. Plastered over.

 

[sparkwright]

Just ordinary twin+earth cable?

Yes, you could - only if it is run in appropriate safe cable zones - but an RCD should be fitted to protect that circuit, as there will be no earthed sheath, and it will be less than 50mm from the finished surface.

 

[flameport]

Can it replaced with 1.5mm using the same concealement method?

Probably - but is there actually any need for replacement? What's wrong with the existing cable?

 

[sparkwright]

Probably - but is there actually any need for replacement? What's wrong with the existing cable?

It sounds like someone has messed about with it and stripped too much sheath off.

I quite like H's idea of using FP200 to replace that one cable, though I don't suppose there is much advantage apart from the fire proof advantage.

 

[Harry Bloomfield]

It sounds like someone has messed about with it and stripped too much sheath off.

I quite like H's idea of using FP200 to replace that one cable, though I don't suppose there is much advantage apart from the fire proof advantage.

FP has an earthed outer, not sure if that would be acceptable in the same way as a Pyro, to avoid the need for the safe zone?

From memory, there were special, shallow 'conduit type' boxes, which allowed the used of Pyro cables without the gland, just the seal on the end termination.

 

[flameport]

All lighting circuits in domestic premises require RCDs now, so the type of cable and installation method doesn't change anything.
There are no zones on ceilings.

 

[sparkwright]

As far as I know FP has never been considered as earth sheathed in the same way as MI or SWA cable.

In fact, I never thought of the metal sheath of FP as being earthed, though I suppose the bare earth conductor inside does come into contact with it.

Also, the metal sheath of an FP could never be used solely as the earth conductor itself, unlike MI or SWA.

 

[333rocky333]

From memory, there were special, shallow 'conduit type' boxes, which allowed the used of Pyro cables without the gland, just the seal on the end termination.