Spacing between LV and ELV?

[nostos156]

Planning on running some conduit for ELV while I get the chance during a renovation. I've seen a bunch of different figures for how much spacing you should keep the LV mains lines from the ELV (Ethernet, HDMI, etc.) to avoid any possibility of EMF interference, although it was mostly American NEC regulations I was seeing.

Figures ranging from 50mm, to 300mm, all the way up to 450mm. Obviously, the further away the better. 450mm seems a bit excessive, but I presume that's what you get when you have them running up two different studs (so say power up left side of one stud and data up right side of the next stud).

What do the regs or pros on the job know how to do it by?

 

[littlespark]

Without looking at my book for details, you can get dado trunking in offices which generally have mains voltage through the centre compartment, and data in the top or bottom.

The entire trunking can be 200mm wide… so that can give a better idea of distances.

 

[nostos156]

Without looking at my book for details, you can get dado trunking in offices which generally have mains voltage through the centre compartment, and data in the top or bottom.

The entire trunking can be 200mm wide… so that can give a better idea of distances.

Thanks. One of the reasons I asked is because when I pulled a wall down to batten it out and rebuild, I found the entry point for the mains cable supplying the entire house in the corner. I was worried that this cable would end up producing far more interference than the regular circuits, and if this would present a problem since it was in the same vicinity of where I'd be running conduit.

 

[Eddy Currents]

Minimum distances really depend on what cable you are using for data / power and whether either or both are shielded

The regs state they shall not be contained in the same wiring system and require running in separate conduit, trunking, tray, ducting or separated by a partition unless insulated for the highest voltage present

The only minimum distance mentioned in the regs is proximity to communication cables underground which need a minimum distance of 100mm or separation by other means as above

 

[pc1966]

In the olden days of analogue phones you would have a real risk of picking up clicks and plops as stuff was switched. Modern twisted pair Ethernet is pretty immune to most things, so you really just need physical containment so they can come in contact, etc.

 

[nostos156]

One last question—do we really only have standard backboxes to tidy in-wall conduits into? Kind of annoying because they all have 25mm knockouts and if you ever need larger, like 32, you're gonna be doing surgery and hope you don't break a knockout while doing so.

The Americans have this worked out much better, with proper stud-affixed in-wall junction boxes. We seem to be way behind in comparison.

 

[davesparks]

One last question—do we really only have standard backboxes to tidy in-wall conduits into?

We have all manner of boxes for all types of application.
Standard back boxes are designed for fitting standard wiring accessories (switches, sockets etc) and fit that purpose perfectly well.

What sort of thing do you need on the end of the conduit?

 

[LewisM]

One last question—do we really only have standard backboxes to tidy in-wall conduits into? Kind of annoying because they all have 25mm knockouts and if you ever need larger, like 32, you're gonna be doing surgery and hope you don't break a knockout while doing so.

The Americans have this worked out much better, with proper stud-affixed in-wall junction boxes. We seem to be way behind in comparison.

We have a vast range of junction boxes and enclosures available just not from screwfix

Metal Adaptable Boxes | Electrical Boxes | Electrical2Go

Buy Metal Adaptable Boxes from Electrical2Go. Fast & Free Delivery. Trade Quality with Low Prices. Click or Call: 01424 220384

www.electrical2go.co.uk

 

[Lucien Nunes]

Spacing distances are a bit of a complex issue to analyse and calculate. Suffice to say, it is not generally as critical as people believe and usually large distances are a matter of a***-covering rather than technical necessity. In the entertainment industry our analogue microphone cables are some of the most sensitive out there, but we routinely run them right alongside power cables for tens or even hundreds of metres. But if one is building something in permanently, one does not want to find that next year's flavour of data is more sensitive and suddenly the 10mm spacing is a problem and the walls have to be ripped out to increase it.

Keep them as far apart as practical, no advantage in going above say 100mm, and no real problem if bits have to be closer.

 

[nostos156]

We have all manner of boxes for all types of application.
Standard back boxes are designed for fitting standard wiring accessories (switches, sockets etc) and fit that purpose perfectly well.

What sort of thing do you need on the end of the conduit?

A gland would be going on the end of the conduit in order to make it tight and stop anything getting in that could crawl through the brush plate. A gland for a 32mm conduit barely fits into a 47mm backbox at the bottom. So a box deeper than 47mm would be a good start.

I have a specific problem where fitting a 32mm conduit into one such 47mm backbox will end up with it being recessed into the wall, because it would be unable to be flush with the plaster (and PIR right behind it), due to having no space for the conduit taking into account the gland connection.

As for why the large conduit - TV cables, etc.

We have a vast range of junction boxes and enclosures available just not from screwfix

Metal Adaptable Boxes | Electrical Boxes | Electrical2Go

Buy Metal Adaptable Boxes from Electrical2Go. Fast & Free Delivery. Trade Quality with Low Prices. Click or Call: 01424 220384

www.electrical2go.co.uk

Those don't look very wall-plate friendly though.

 

[davesparks]

I specific problem where fitting a 32mm conduit into one such 47mm backbox will end up with it being recessed into the wall, because it would be unable to be flush with the plaster (and PIR right behind it), due to having no space for the conduit taking into account the gland connection.

Back boxes rarely end up flush with the plaster, that's why extension collars exist.

 

[littlespark]

Back boxes rarely end up flush with the plaster, that's why extension collars exist.

Nah…. That’s why long screws exist

 

[nostos156]

So one thing I didn't consider before doing the run, but having encountered it, was it turns out the mains cable supplying the whole house from outside was near where I'd be putting the conduit. That cable was a chunky thing, and I think I saw 600/1000v on the sheathing when I had a look.

I ran the conduit at a distance of 50cm from it, as that kept the conduit 50cm from both the mains cables to sockets below, and the mains house supply that ran above said conduit.

Question is, since that cable seems much higher rated than all of the other 240v cables, and supplies electricity to the whole house, was 50cm spacing sufficient? I can't find much info on the really high voltage stuff.

 

[littlespark]

Don’t worry. The cable is rated to 600v, but the supply is 230. You won’t get any more than that normally.

This chunky cable…. Is it black and round? It could be swa, or concentric if it’s a suppliers cable. Both have earthed outer cores which will act as a shield

 

[nostos156]

Don’t worry. The cable is rated to 600v, but the supply is 230. You won’t get any more than that normally.

This chunky cable…. Is it black and round? It could be swa, or concentric if it’s a suppliers cable. Both have earthed outer cores which will act as a shield

Yeah, it is black and round. It was also fairly heavy (it was being suspended halfway up the attic by a single screw, purposefully bent… I lifted it up higher using saddles I had that I wrapped in PVC tape, to get the 50cm spacing). Sounds like it was a concentric as it should be a supplier's cable, I can see where it enters the house.

Good to know it won't be an issue.