UK Running conduit in walls to knockout boxes for low voltage cables?

[BillMcLeod]

Background

I'm running some low voltage cable (e.g. CAT6A data cable; coax cable; HDMI cable and speaker cable) to a number of rooms of the house and would like advice on the best way to do this to avoid plastering the cables into the walls - to give me flexibility to remove / pull new cables in the future (if needed) without having to re-plaster.

It's an old 1915 house with thick plaster walls. We'll be lifting the floorboards, running the cable underneath, and then chasing out a channel in the walls up to a new cutout for a 35mm 2-gang knockout box. Each 2-gang knockout box will be fitted with a 4-module euro plate and the appropriate modules e.g. 2 x RJ45 euro module; 1 x ftype euro module; 1 x HDMI cable euro module.

The knockout boxes have 20mm holes, so I am assuming that I can run 20mm conduit from the bottom of the knockout box, down the chased wall channel and then under the floorboards.

My questions are:

1. What type of conduit to use? Rigid 20mm PVC? Flexible 20mm Conduit? Any particular brands / suppliers recommended?
2. How do I couple the conduit to the knockoutbox?
3. Am I best only running the conduit as far as under the floorboards (to stop them being plastered in) or should I try to run them all the way back to 'base'?
   1. The advantage of doing the full conduit 'back to base' would presumably allow me to pull new cable without lifting carpet or floorboards, but this isn't the biggest pain in the world if I need to do it... Having to re-plaster and re-decorate would be a bigger nuisance.

 

[R-fur]

I would use 20mm rigid conduit. You can buy couplers to connect them to the boxes. Conduit all the way back would be good if the runs are not too long, but I would be happy with drops to just below the floor.
There is not much difference between makes of conduit, just go with what you can get, the couplers can just be pushed on but its better if you glue them. Whoever supplies the conduit should have the glue as well, its solvent weld type of stuff.

 

[JK-Electrical]

What type of conduit to use? Rigid 20mm PVC? Flexible 20mm Conduit? Any particular brands / suppliers recommended?

Either of the two would suffice.

How do I couple the conduit to the knockoutbox?

For PVC conduit you would use either of these adaptors:

Marshall Tufflex MA7BK Black Round Conduit Male Thread Adaptor 20mm, MA7BK - http://www.discount-electrical.co.uk/product.php/1457872/marshall-tufflex-ma7bk-black-round-conduit-male-thread-adaptor-20mm

http://www.discount-electrical.co.uk/product.php/1457885/marshall-tufflex-ma8bk-black-round-conduit-male-thread-adaptor-25mm

You may need some of these too to secure the conduit to the wall:

http://www.discount-electrical.co.uk/product.php/1444089/marshall-tufflex-mmc2bk-black-round-conduit-u-clip-20mm

If you opt for flexible conduit, here's a cheap solution:

Budget NFB-CP21B 20mm Contractor Pack With 10m Polypropylene Flexible Conduit Reel, 10 x Adaptors & Locknuts, NFB-CP21B - http://www.discount-electrical.co.uk/product.php/382195060/budget-nfb-cp21b-20mm-contractor-pack-with-10m-polypropylene-flexible-conduit-reel--10-x-adaptors---locknuts

Am I best only running the conduit as far as under the floorboards (to stop them being plastered in) or should I try to run them all the way back to 'base'? The advantage of doing the full conduit 'back to base' would presumably allow me to pull new cable without lifting carpet or floorboards, but this isn't the biggest pain in the world if I need to do it... Having to re-plaster and re-decorate would be a bigger nuisance.

Running the conduit back to base isn't really a viable option unless it's a very short, straight run. If there are any bends in the run, you would need to fit angle boxes:

Marshall Tufflex 2MRB4BK Black Circular Angle Conduit Box (2 Way) 20mm, 2MRB4BK - http://www.discount-electrical.co.uk/product.php/1457733/marshall-tufflex-2mrb4bk-black-circular-angle-conduit-box--2-way--20mm

The problem is that if you decide to install additional cabling at some future point, you would then need to lift the carpets and flooring to access the boxes which kind of defeats the purpose of installing an underfloor conduit run in the first place! You could always run a draw-wire between your base-point and the point nearest to where your cabling will enter the chase you'll be cutting in the wall, and use that to install any future cables.

 

[Pete999]

I would use 20mm rigid conduit. You can buy couplers to connect them to the boxes. Conduit all the way back would be good if the runs are not too long, but I would be happy with drops to just below the floor.
There is not much difference between makes of conduit, just go with what you can get, the couplers can just be pushed on but its better if you glue them. Whoever supplies the conduit should have the glue as well, its solvent weld type of stuff.

You should ALWAYS glue them with the correct adhesive they are NOT push fit. Just imagine the hair pulling heartache if the UNGLUED joits came apart when you are trying to pull cables through, don't bare thinking about, do it once and do it right first time as Mike Holmes would say.

 

[littlespark]

For 2 cat5 cables, a co-ax for the ftype, speaker cables etc etc, I would think 2 x 20mm conduit drops per point.

I’m thinking of the capacity of 20mm to take that number of cables. Also got to think of the future if you decide to pull in a new cable alongside existing.
As suggested, make sure the adaptors are glued on.... and if your putting a bend in the conduit you can either buy pre made 90’ bends which have to be glued on as well, or use a bending spring. That is an art form in itself

 

[davesparks]

You should ALWAYS glue them with the correct adhesive they are NOT push fit. Just imagine the hair pulling heartache if the UNGLUED joits came apart when you are trying to pull cables through, don't bare thinking about, do it once and do it right first time as Mike Holmes would say.

For surface work I completely agree, but when it's being plastered in such as this scenario the conduit won't move anywhere if it isn't glued

 

[radiohead]

You should ALWAYS glue them with the correct adhesive they are NOT push fit. Just imagine the hair pulling heartache if the UNGLUED joits came apart when you are trying to pull cables through, don't bare thinking about, do it once and do it right first time as Mike Holmes would say.

You don't have to always glue conduit and it can be push fit. As long as it is properly supported and secured it will never come apart. Coming apart is only a problem with insufficient saddles, and boxes not fixed, poor workmanship in other words. I rarely glue plastic conduit.

 

[davesparks]

You don't have to always glue conduit and it can be push fit. As long as it is properly supported and secured it will never come apart. Coming apart is only a problem with insufficient saddles, and boxes not fixed, poor workmanship in other words. I rarely glue plastic conduit.

Any surface mounted PVC conduit should be glued, with the exception of expansion couplers. PVC conduit moves too much on its own through expansion and contraction to not be fixed together.
I doubt any manufacturer will approve of it being installed without gluing.

 

[Megawatt]

You don't have to always glue conduit and it can be push fit. As long as it is properly supported and secured it will never come apart. Coming apart is only a problem with insufficient saddles, and boxes not fixed, poor workmanship in other words. I rarely glue plastic conduit.

I’ve got to agree with Pete999 that you should always glue your conduit. Also run redundant conduits with pull strings

 

[Andy78]

I’ve got to agree with Pete999 that you should always glue your conduit. Also run redundant conduits with pull strings

Draw strings aren't always necessary over here. I think you tend to install longer runs over there. We have a regulation that asks for adequate means of access (drawing boxes etc) for containment intended for cables to be drawn into.