supporting vertical conduit

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I want to run a 4mm cable from the loft to the garage, inside a duct which is currently used for plumbing. I propose to use 25mm flexible conduit, put it down the duct and secure it, then poke the cable down from the top.

How many saddles should I use for the conduit? Do I need a particular support for the weight of the cable at the top?

The drop is 8 or 9 metres.
 
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I want to run a 4mm cable from the loft to the garage, inside a duct which is currently used for plumbing. I propose to use 25mm flexible conduit, put it down the duct and secure it, then poke the cable down from the top.
As a matter of interest, why are you putting conduit inside ducting?

Kind Regards, John
 
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Because I want to put in the conduit before the installation. The installer doesn't want to work on the duct. My idea is that they can just poke down, once I've fitted it.

there are also alarm cables in the duct. I want to keep them apart.
 
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My idea is that they can just poke down, once I've fitted it.
I'm sure it is.

Will the ducting be easy to make good/repair/replace once they give up trying to push the cable down the conduit and have to remove the ducting instead?
 
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You won't push a cable down a flexi conduit easy ! Use solid conduit or put in a draw cable before.
 
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I wouldn't use flexi conduit. It's a PITA to pull cables into if you can't "handle" the conduit.

Put some 25mm rigid in. It's cheaper too.

How many cables, and what size?

I worked on a site with pre-built rooms being brought together to form a hotel. Flexi conduit was put in for the rooms smokes/sounder and phone. So many rooms ended up needing the ceilings re artexed ;)

The mains cabling wasn't conduited. It came out as 2x2.5 and 1x1.5 above the hall suspended ceiling to be taken to a small DB for every 4 rooms.
 
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Do I need a particular support for the weight of the cable at the top?.

If the cable goes from horizontal to vertical at the edge of a joist then fit a curved surface to avoid a sharp bend in the cable.

As said you will have difficulty in pushing cable into a conduit. Use a draw cord to pull it while someone else feeds it in. Feed straight from the reel with no kinks or twists in the cable.

An 8 metre drop is not a good idea with "ordinary" PVC cable. Better to separate it into two 4 metre drops with good support between the two sections.
 
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Did you mean

A flexible cable shall be used for fixed wiring only where the relevant provisions of the Regulations are met. Flexible cables used for fixed wiring shall be of the heavy duty type unless the risk of damage during installation and service, due to impact or other mechanical stresses, is low or has been minimized or protection against mechanical damage is provided.


or did you mean something useful?
 
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returning to my original question about spacing of the saddles, I gather that

The spacing for 16-25mm conduit is:
1.75m horizontal and 2.0m vertical for rigid metal
1.5m horizontal and 1.75m vertical for rigid insulating
0.4m horizontal and 0.6m vertical for pliable


So if I change to rigid conduit, it would be 1.75m spacing. I have access panels to the duct so can do that.

I have ordered inspection bends for the top and bottom.

The cable will be clipped horizontally along the wall at top and bottom before it enters the conduit..
 
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For vertical rigid conduit solvent welding the conduit to the upper most saddle will stop it sliding down and out of the saddle over time. Allow space at the bottom for expansion, especially if heating pipes are in the same cavity. It will slide through other saddles when it expands and contracts. On a long drop use two saddles close together at the top with the conduit glued to both.

Only glue to the U shaped part, also use wood screws through both the U and the saddle base and into the wall. The short screws into the soft plastic base do not provide much support.
 
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I would probably use cable cleats or galv conduit saddled to hold it. It's out of site, so no need for white ones. The plastic ones are not too robust.
 
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