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.

 

[Barnaby Stedman]

could you just make it clear where these joists are? you dont seem to have mentioned them in your explanation of the cable run?

 

[telectrix]

if the joists have free air below, i.e a cavity, , then just clip the cable to the underside.

 

[David Searls]

could you just make it clear where these joists are? you dont seem to have mentioned them in your explanation of the cable run?

The consumer unit is contained in a ground floor flat. Beneath the flat is a cellar which runs front to back under the flat. The main issue is that the cellar is not private to the flat alone. The utilities gas/electrics/water for all the flats are located there. So I am little concerned not to introduce a 10mm cable which will eventually be connected to a high rated fuse in an exposed situation in a "shared/common" place. It is possible to walk stooped in the cellar, trying not to bump a head into the water pipes running under the joists.

I did not think it was allowed to just clip cable to the underside of joists in case they are accidentally damaged. Not really an issue if the cellar was totally private but public..? Don't know.

There are holes already in the joists for existing cabling introduced before I arrived. Unfortunately they are not located between 0.25 and 0.4 the length of joist away from then end. So not ideal. Luckily the holes only run along one side of the relevant joists. The other sides of all the relevant joists are untouched.

There are 8 joists that need to be traversed before getting to the wall on the other side of which is the flat's private garden.

As well as traversing the joists the cabling will need to run parallel to the joists for about 2.5m to get to the right point on the wall where drilling will take place to get into the garden. Only mention this in case it affects any conduit radius/junction box issues.

I am installing tiles onto the floor supported by some of the the joists I have limited scope for the subfloor beneath the tiles which in turn impacts on the amount of flex the joists can allow before the tiling is affected. Hence trying not to weaken the joists if at all possible.

Thanks.

 

[David Searls]

if the joists have free air below, i.e a cavity, , then just clip the cable to the underside.

Yes plenty of cool free air under the joists. But I did not think it was allowed to just clip cable to the underside of joists in case they are accidentally damaged. Not really an issue if the cellar was totally private but public..? Don't know.

Not really keen to be honest running 10mm in the public space at all.

Figured get it installed now that consumer unit wall is open. And in the future there might be enough armoured cable anyway to run all the way from the garage to a junction box located just underneath the consumer unit where it comes through the floor. Replacing the 10mm standard T+E run in the cellar with armoured.

When I say "public", I should say shared with the other flats in the house. Explained better in my reply to Barnaby Stedman.

Thanks.

 

[DPG]

I'm not 100% clear on the route. Does the route for the twin and earth comply with regulations for not having RCD protection?

Is it the old colours then?

 

[MJPD29]

Running it through the joists is fine. 15 years old? Is it red&black?

 

[Yozza19]

Shove it in some 20mm plastic tube with metal sadles I would also use a rcbo if I was you

 

[Toneyz]

If you are installing the pvc/pvc in a wall at a depth equal or less than 50mm that is open at the moment?

 

[Nebu1a]

Is the cable you want to use from 2003/2004 in non harmonised colours?

"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."

I know you want to future proof but in your situation with the public cellar I would run your SWA cable back to your consumer unit. You could fit a batten to the underside of the joists and clip/ cleat the cable to this.

 

[David Searls]

I'm not 100% clear on the route. Does the route for the twin and earth comply with regulations for not having RCD protection?

Is it the old colours then?

Unfortunatly no spare ways left on the RCD side of the Consumer Unit. However when time comes to finish job could
upgrade Consumer Unit if necessary. Then again figured on implementing the RCD function in the New Consumer Unit in the garage.

Yes probably old colours. White outer sheath, Black and Red and Earth Inside.

 

[David Searls]

Running it through the joists is fine. 15 years old? Is it red&black?

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?

 

[David Searls]

Shove it in some 20mm plastic tube with metal sadles I would also use a rcbo if I was you

Will it fit in 20mm/25mm even plastic (oval?) tube? Metal sadles, sounds interesting? Any links. Existing Wilex consumer unit probably
too old/shallow to fit rcbo, will hit against neutral bar. But when time comes to complete job might well upgrade Consumer Unit.
Plan also to have RCDs also in garage consumer unit. In fact will probably use current CU in garage and install new CU with rcbo's
in flat. No tripping Freezer?

 

[David Searls]

If you are installing the pvc/pvc in a wall at a depth equal or less than 50mm that is open at the moment?

Its just a stud wall. Existing wires just hanging down and then dropping through holes in floor plate. So just
adding another cable. However, now that you mention it, I think I will try to ensure that all the cables are centered between plaster boards.

 

[David Searls]

Not sure, I think it must be old colours. Red, Black and Earth.
I agree ideally. But would be great not to have to open up wall again.
But SWA back to Garden Wall, junction box as planned?
Or better still SWA back to a junction box at the first joist located beneath consumer unit? Except that I feel uncomfortable having the junction box in the
shared space and not in the private garden on the other side of the wall.

Very much like the idea of the batten as you described.
My original idea was two battens, with the cable in-between, perhaps with steel capping. But this also serves to conceal the cable contained.

I think your idea is better. The wooden batten should protect the cable, unless they are wearing viking helmets and carrying spears.
And the cable would be visible so people would hopefully know not to go near with an angle grinder? I suppose you have to assume that people
do not have a death wish? Then again.... And being open no chance of heat buildup.

So maybe fix a 1"x2" or 1"x3" to the bottom of the joists and then clip the cable high up against the side of the batton and just under the joists?
And then maybe a further batton on the other side of the cable so it is even more protected?

Sounds good to me, but would building control/electrical contractor, disapprove?
I'm worried that there is some regulation in the 17th or 18th that forbids this?

 

[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.