Running 10mm T+E under celler joists.

[David Searls]

Hello,

Whilst doing some building works I have access to the inside of the stud wall to which the consumer unit is fitted, so full and easy access to all the cabling there. This wall is soon to be tiled.

In the future I will want to put power into a garage at the end of the garden.

I happen to have some 10mm Twin Core and Earth left over from a rewire I did 15 years ago.

What I would like to do is to run the 10mm from a spare way on the non RCD side of the consumer unit, down through the floor, into the "Common Space" cellar (not quite standing room) and run it to the wall on the other side of which is the private garden.
Drill a hole in the brickwork of that wall, pass the cable through and terminate it there in the interim.

A hole drilled there would come out underneath the floor of a raised conservatory. A junction box there would be easily accessible albeit with a lot of stooping and semi crawling. But it is dry there. The right hand edge of the conservatory (On wooden legs) floor, is about 18" from where the IP66 junction box would be located.

The plan would be to add a 6amp lighting breaker to the spare slot in consumer unit to which the 10mm would connect. And leave it turned off.

I know 10mm sounds like a lot, but I have plenty of it, just lying there, and the plan is to future proof, enabling me to use a welder in
the garage.

I would prefer if any way possible, not to have to drill holes (weaken) all the joists which run parallel to the "garden wall".
I would prefer to use conduit fixed to the under side of the joists.

Questions:
1. Is it permissible to connect conduit to the underside of joists or must the cable run through the joists?
2. If permissible would the conduit have to be metal or could it be plastic?
3. If metal can somebody point to the most appropriate conduit/trunking to carry 10mm T+E whole within its sheathing.
4. I read on one forum (wish I could find it again) that it used to be practice, to make up a protected run using wooden battening, again
fixed to the underside of joists. Would this now be against regulations? This might be easiest for me

In the future I would want to connect the terminated 10mm cable to a new consumer fitted in the garage, using armored cabling running under the garden. Then up rate the mini breaker to more appropriate one in the house consumer unit.
I could do that without opening up the wall again which by that time will be tiled.

When the time comes I will try to get an electrician to advise on how to safely bury/run the armored cable and then later to connect up,
commission and certify the installation.

Clearly I am not a qualified electrician, but as stated I did a full rewire about 15 years ago, including the consumer unit.
It was ok (I think) for the non qualified to do that then (it was all explained in a general DIY book)?! And afterwards I had the work checked out anyway.

As with many people I suspect, I have had the odd shock in the past, enough to have given me a healthy respect for electricity and never assume a connection is not live until tested.

Can understand if nobody wants to advise but any advice appreciated.

 

[DPG]

I'm struggling to picture this to be honest. Any chance of photos?

And again, does the routing of the cable comply with it not being RCD protected?

 

[Silly Sausage]

Personally, I'd forget all about the 10mil and do the whole run in SWA.
A lot less hassle, and you won't need the cable joint on the outside wall, bound to be a water based problem in the future!

 

[davesparks]

Yes Red and Black, does Cable have a shelf life?

Cable doesn't have a shelf life, but the regulations changed to require new installation work to use brown and blue rather than the old red and black. So technically installing this cable now does not comply, though some electricians may make an informed departure from the regulations.

 

[davesparks]

My advice is to forget about the T&E and just install a conduit with draw wire in the wall so that the SWA can be pulled in to it when it is installed thus avoiding any joints in a new circuit.
Th conduit would need to come out if the wall below the CU to allow fitting of the gland but could be covered with a blank plate for now.

 

[MJPD29]

Yes may end up running through the joists on the untouched ends. Between 0.25 and 0.4 new holes. Should be ok.
Yes Red and Black, does Cable have a shelf life?

It'll be fine, but sleeve the colours brown and blue to keep everyone happy

 

[David Searls]

I'm struggling to picture this to be honest. Any chance of photos?

And again, does the routing of the cable comply with it not being RCD protected?

Not positive but I think the fact that the cable will be visible after exit from the bottom of the CU stud wall permits Non RCD? If taking the
T/E to SWA approach, yes the SWA length would be buried, but this part would be to spec as directed by a contracted electrician.
It is not intended that any of the 10mmm T/E will be embedded at any point, say in masonry (except when it passes into the garden directly through the cellar wall).

 

[David Searls]

My advice is to forget about the T&E and just install a conduit with draw wire in the wall so that the SWA can be pulled in to it when it is installed thus avoiding any joints in a new circuit.
Th conduit would need to come out if the wall below the CU to allow fitting of the gland but could be covered with a blank plate for now.

Thanks davesparks (and thanks Archy Styrigg). Draw wire sounds like a good approach.

If I understand correctly I would need to leave a pull wire through an appropriately sized hole in the Stud Wall foot plate. The hole would need to be large enough to accept the diameter of the SWA.

There are no noggins below the Consumer Unit, so perhaps no need for a temporary conduit, if this is what you meant.

The only problem is that the Noggin at the height of the consumer unit. As well as supporting the consumer unit, it helps to support the weight of the cables exiting the back of the CU before dropping down. But then it also narrows and impedes the route into the back of the CU.
I think regardless of any conduit it will make it difficult for the electrician to pull in the SWA.

However I imagine that it might be possible with the main fuse switched off to temporarily unscrew the whole of the CU and pull it away enough from the wall to enable a cable to be pulled up and worked through the back. Just guessing. Perhaps electricians have other standard tricks to overcome this particular
issue.

Tricky, but it would be great to have the whole run in SWA and installed by an electrician. Let me off the hook? Food for thought.

I investigated a socket today feeding the boiler. It was 1.5 T/E. But could not find a corresponding FCU anywhere to correspond.
From the cellar I could see two 2.5 T/E main loop cables disappearing up into masonry but on the wall a single 1.5 T/E. It had been doing my head in for a few days.
I brought in a wire detector to try and trace. Was not sure if the detector would be any good through masonry (very cheap unit I bought years ago).
The 2.5 T/E were buried JUST beneath the surface of a separate of a adjoining wall and were picked up by the detector. No question of Permitted Zones here!

Chiseled out the 2.5 T/E in its plastic sheathing up to a standard 30Amp junction box, where it output 1.5 T/E round the corner.
The tough plastic junction box even had metallic plates plastered in front. But the hidden cables dropping down, hidden just beneath the surface, just begging for a nail was.. well Shocking!
Was this ok practice in the 80's when the original conversion I believe took place?

This is the third Hidden electrical outlet I have found! But the worst so far.

Thanks to all.

 

[David Searls]

It'll be fine, but sleeve the colours brown and blue to keep everyone happy

Thanks, good to know about this solution.