T&E in conduit in screed?

[JohnW2]

That did occur to me today You are correct, the mechanical protection is the same whether earthed or not - but if it's not earthed then drilling and screwing through it could make it live. It's most likely that the circuits will be RCD protected - but if the trunking is earthed then the cables within it don't need to be (though elsewhere they probably will).

Yes, all agreed. As I'm sure you realised, I was merely teasing you about your choice of wording

Kind Regards, John

 

[sparkwright]

Considering only a 1.5m length will be under the screed, and assuming the installation comprises of T&E, isn't the op better off using 20 or 25mm plastic flexible conduit - as he orginally suggested?

Would be advisable to only run one or two cables in each though.

 

[SimonH2]

The problem with flexible conduit is that it's corrugated and a right PITA to thread things through. Depends on how future proof the OP wants it to be.

 

[JohnW2]

Considering only a 1.5m length will be under the screed, and assuming the installation comprises of T&E, isn't the op better off using 20 or 25mm plastic flexible conduit - as he orginally suggested? ... Would be advisable to only run one or two cables in each though.

Indeed. I'm not so sure about flexible plastic conduit (if that means the stuff with a 'corrugated' inside) (unless,perhaps, it were only 'one cable per conduit') but, if it were me, I think I would indeed be considering several plastic conduits.

Kind Regards, John

 

[sparkwright]

I have successfully got T&E cables through considerably 20mm corrugated flexible conduit.

It's not very difficult.

I wouldn't recommend more than one cable in a conduit, two at the most.

The beauty of the corrugated stuff makes it easy for bends and obstructions.

I wouldn't use this if you want a guaranteed method of rewiring in the future mind.

 

[JohnW2]

I have successfully got T&E cables through considerably 20mm corrugated flexible conduit. It's not very difficult.
I wouldn't recommend more than one cable in a conduit, two at the most.

That's almost the same as what I said - except that (on the basis of past experiences!) I would personally not attempt to get more than one T+E through 20mm corrugated flexible conduit.

The beauty of the corrugated stuff makes it easy for bends and obstructions.

That's certainly true, but it seems that their are varying opinions/experiences as regards the balancing downsides (if one tries to put more than one T+E through it).

Kind Regards, John

 

[SUNRAY]

That's almost the same as what I said - except that (on the basis of past experiences!) I would personally not attempt to get more than one T+E through 20mm corrugated flexible conduit.
That's certainly true, but it seems that their are varying opinions/experiences as regards the balancing downsides (if one tries to put more than one T+E through it).

Kind Regards, John

I'd not use flexible for this unless you go up to 32mm.
one 2.5 T&E in 20mm that length will be fiddly,
two 2.5 T&E in 25mm will be easier.
three 2.5 T&E in 32mm will be even easier.
This assumes all cables are drawn in together.

Straight conduit is smoother and a larger bore if lightweight tube is used and therefore easier to draw cables in.

 

[ban-all-sheds]

Considering only a 1.5m length will be under the screed, and assuming the installation comprises of T&E, isn't the op better off using 20 or 25mm plastic flexible conduit - as he orginally suggested?

All those suggesting that rather than proper floor trunking must know of a reason why proper floor trunking is inappropriate in this case.

 

[rsgaz]

must know of a reason why proper floor trunking is inappropriate

I am assuming that this is for a kitchen island, so the containment needs to turn up at either end. Floor trunking riser bends are horrid, I've never seen a swept bend, only an awful 90° bend or a 'slightly better' double 45° bend, such as...

Unless the OP has walls about 8 inches thick, then that can't be chased into the wall and still meet the one third depth rule. Pulling cables through after is has been set under the screed and plastered over in the wall causes the sheath to be damaged on the bends, especially when some screed/plaster has leaked through and made it nice and rough! Abrasive in fact! Unless you are going to make it totally water tight first.

Also, I'm assuming he will be having a large grid system wall box for all the switches...

Floor trunking won't mate very well with it, whereas conduit clearly will. You can see with that particular box I have shown, it has three 20mm knockouts along the bottom. They could easily be enlarged to 25mm and add two extra 25mm holes between them, so 5 25mm conduits, all ran in singles would be ideal. Nice swept bends, easily presentable at either end.

 

[rsgaz]

Also, he only has 55mm depth to play with. Floor trunking is springy to stand on before it's been screeded over. If he ends up with, say, only 10mm of screed on top, it will soon break up from walking on it.

Edit: Although I did just find some which is only 25mm tall, but it's very wide, so cracking could still be an issue.

 

[sparkwright]

All those suggesting that rather than proper floor trunking must know of a reason why proper floor trunking is inappropriate in this case.

I wondered if it was too expensive, too overkill, and too specialised for a simple 1.5m run in a house - but I'm open to opinions.

 

[JohnW2]

I wondered if it was too expensive, too overkill, and too specialised for a simple 1.5m run in a house - but I'm open to opinions.

I'm inclined to agree. Indeed, if I were in the situation we're talking about, I think I might be tempted to run each cable (separately) through the screed in hosepipe!

Kind Regards, John

 

[SimonH2]

I am assuming that this is for a kitchen island, so the containment needs to turn up at either end.

I would leave a large hole in the screed under the island rather than put an extra bend in the conduits. Doesn't help at the outer wall, but it's one less bend to negotiate.
At the wall end, perhaps use of a conveniently placed cupboard to hide the conduits ?

 

[rsgaz]

perhaps use of a conveniently placed cupboard to hide the conduits ?

Yeah, maybe, depends on the layout I guess, but I'm still rooting for it to be wired in singles. Takes up less space in the conduits, therefore needing less(or smaller) conduit and is easier to pull in. So the conduits would have to continue up at both ends for the scenario I have recommended.

 

[sparkwright]

I can't help thinking that singles could prove to be a PITA.

As I understand it, nine or ten conduits wouldn't be a problem.