Cable trays?

[Alan Ambrose]

OK another tech question...

 

We have a 50mm services void. I was planning to run horizontal cable trays, mostly high-up (2.5m above the floor) and split into mains & ELV / data (either using one split tray or two separate trays). Then a few vertical drops to light switches etc, also in trays if I can. And then fill any remaining void with, say, mineral wool.

 

Question is - how do I avoid the mains crossing the data or is that OK? Something like this:

 

Mains ------------------------!-------------------------------

Data   ------------------------!---------------!----------------

                                                  !                         !

                                                  !                         !

                                       Mains Socket     Network Port

 

 

[garrymartin]

Perfectly fine. Crossing has fewer issues than running in parallel, and even that is not a big deal given the number of cables and voltages we are talking about in residential construction.

[ProDave]

BUT electric cables must tin in safe zones.  So to ensure this the electric cable tray must be within 100mm of the ceiling all the way across the room.

 

The data cable tray can be at any height you want.

[Alan Ambrose]

>>> the electric cable tray must be within 100mm of the ceiling

 

Ah, I was assuming some common sense on this  - we’re vaulted pretty much everywhere with a slopey ceiling from about 3.5m at the eaves. I was planning on putting the trays above the doors at about 2.4m.

[Alan Ambrose]

p.s. I was thinking re safety standards / British standards / building control etc rather than interference problems. I see a typical summary e.g. here:

 

https://www.cablemonkey.co.uk/cmdocs/ElectricalDistance.pdf

 

But it has so many cases, it’s really hard to follow.

[ProDave]

1 hour ago, Alan Ambrose said:

>>> the electric cable tray must be within 100mm of the ceiling

 

Ah, I was assuming some common sense on this  - we’re vaulted pretty much everywhere with a slopey ceiling from about 3.5m at the eaves. I was planning on putting the trays above the doors at about 2.4m.

Electric cables in a wall must run in a safe zone.

 

Broadly speaking a safe zone is horizontally or vertically from an electrical accessory, e.g. a socket, or within 100mm of the corner of a room or ceiling.

 

If you want to run electric cables around a room then do so at socket height, and ensure each wall has at least one socket to create that safe zone, and that is where all your mains cables can correctly run around a room.

[Alan Ambrose]

@ProDave So, I just need to put a dummy 'point, accessory or switchgear' to establish a zone / cable tray anywhere I like? 😄

 

I'm sure I need some temperature/humidity sensors up at 2.4m 😉

 

[ProDave]

Yes that is exactly what you need to do.

[-rick-]

Or cap the tray with 3mm steel?

[Nickfromwales]

Why cable tray? Lots of expense and faff. 
 

All round patent band is fine for bunching and laying, and clips are less time consuming than hundreds of cable ties. 
 

Seems a massive ball-ache and cost for very little practical return? You’ll need spacers behind the trays to get cable ties in / out, so further projection outwards too. 
 

Rows of 38x 25 and 38x 16mm trunking would be quick and simple, using the self adhesive to lay these out and then a few mechanical fixings to corners and joints where you’ll be pulling on them. 

[Alan Ambrose]

Why? To give a fighting chance of running a new cable or replacing an old one. The current model when we hide the cables and assume they will be OK for the life of the building seems to me a bit flawed 😉.

[-rick-]

42 minutes ago, Alan Ambrose said:

Why? To give a fighting chance of running a new cable or replacing an old one. The current model when we hide the cables and assume they will be OK for the life of the building seems to me a bit flawed 😉.

 

Im not sure how a cable tray helps you run additional cables later. The ties for the cables and all the perferations will present more snag challenges for pulling cables behind plasterboard than bare trunking or similar.

 

I too want to be able to add additional cables later (especially low voltage/data/hdmi/etc) and am curious what other people think is the best way to go but personally don't think cable trays would help.

 

My best guess at the minute for how to do this is to form two parallel cable paths horizontally along the wall behind the sockets with the metal back boxes mounted in front. Depth is a bit of an issue though. 50mm cavity + plasterboard on top is ok. Less seems to get tricky.

 

Main reason for me to want this ability if I get a chance to build I want to get the basics in and done and then come back and be able to fit 'smart' stuff in a suitable way without ripping up the walls. I don't really want to have to plan where every device cable goes (and what type is needed) before being able to crack on with the rest of the property.

[Alan Ambrose]

>>> I don't really want to have to plan where every device cable goes

 

... for the next 50 years...yeah, exactly.

 

I figure I have a good chance of using a fish tape or electricians rods to run a new cable assuming the runs are fairly straight and there's access at any corners. Maybe it helps that our room layout is fairly simple & rectangular.

[Nickfromwales]

Thinking you’re going to be able to add cables , retrospectively, is a little optimistic; myself, I think it’s practically unachievable.

 

You’d be into breaking in / out of plasterwork, going up / down walls filled with (supposed to be filled with) acoustic insulation, and other services.

 

It’s just way to hard to plan what’ll need to go in, and from where, and to where its “then” needed, to be a realistic approach.

 

You’d need a complete redundant conduit network left in abeyance, throughout the dwelling, to ever attempt to mitigate this sensibly. 

[andyscotland]

On 11/04/2026 at 12:39, Alan Ambrose said:

@ProDave So, I just need to put a dummy 'point, accessory or switchgear' to establish a zone / cable tray anywhere I like? 😄

 

I'm sure I need some temperature/humidity sensors up at 2.4m 😉

 

I'd argue that to create a safe zone it should really be an actual mains accessory or junction/cable box.

 

If it's just a battery powered unit or a blank plate, there's a risk someone pops the lid, sees there's no cables going out of it, and assumes the walls beside/above/below are fine to drill.

 

2 hours ago, Alan Ambrose said:

>>> I don't really want to have to plan where every device cable goes

 

... for the next 50 years...yeah, exactly.

 

I figure I have a good chance of using a fish tape or electricians rods to run a new cable assuming the runs are fairly straight and there's access at any corners. Maybe it helps that our room layout is fairly simple & rectangular.

 

I think it'll be very hard to fish along a cable tray, and even if you could as others have said you can't then fix the cable to it at intervals so it will not be properly supported meaning a) mechanical stress and b) could droop below the safe zone.

 

Conduit or enclosed trunking would be best for fishing, but obviously you'd have to cut a new hole in the bottom if you want a new vertical drop out of it so that would mean opening up that bit of the wall at least.

 

I'd agree with @ProDave the best option is to run all the cables at socket height with at least one socket on each wall.

 

Like @-rick- says, if you run a 50mm batten horizontally on every wall aligned with the base of your sockets, with a gap above it, you have formed a natural "cable tray" / trunking out of your wall construction without any extra materials.

 

You should be able to fish new cables horizontally along that batten, drop vertically down to it from above, etc, with minimal disruption. So long as you only use max 35mm backboxes there will be plenty of space to pass cables behind them, you could just about get behind a 47mm backbox (as 12mm of that will be in the plasterboard).

 

If you want a second zone for data cables then run another batten above or below (depending on whether you think you're more likely to need to add vertical runs for mains or data).