Another cable routing question

[kjm424]

This is yet another cable routing question I'm afraid.

I'm planning to mount my TV on the wall, and so need to get power up behind the bracket. There is a double socket down and to the right from where the TV will be mounted, about 30cm from the floor (diagonal distance from TV bracket to socket is about 2m). This socket is part of the ring main.

I plan to take a spur from this double socket, but I'm wondering how to route the cable. The walls are dry-lined blockwork. I've removed the skirting boards (we're laying laminate flooring), so I am considering running the cable vertically down from the double ring socket, along the wall behind the skirting, then vertically up to the spur socket.

I understand the the horizontal run along the wall at floor level (just below floor level actually) would not be in a safe zone, so would need extra protection. I haven't got a copy of the building regs - would someone be able to advise how to proceed?

My current thinking is to by a length of steel conduit for the horizontal run, but are there any other options? Would armoured cable comply, or maybe use cable with earthed metallic covering?

Thanks.

 

[rebuke]

If I understand your layout correctly, could you not just come down from a FCU (fused connection unit) behind the TV, and then across in to the existing double socket. The FCU makes the vertical bit in a safe zone, and if you go across in line with the horizontal socket then that's in a safe zone as well, so all is fine?

 

[kjm424]

If I understand your layout correctly, could you not just come down from a FCU (fused connection unit) behind the TV, and then across in to the existing double socket. The FCU makes the vertical bit in a safe zone, and if you go across in line with the horizontal socket then that's in a safe zone as well, so all is fine?

Yeah, I guess this is the proper way to do it. The wall is dot-dab dry-lined, so I'd need to cut the board for the horizontal run - something I'd like to avoid if possible.

 

[rebuke]

What is the floor made of, if it's floorboards, then you could just go straight down the wall from FCU, loop round under the floorboards, and back up in to the socket. Obviously if it's concrete that won't work though...

 

[kjm424]

What is the floor made of, if it's floorboards, then you could just go straight down the wall from FCU, loop round under the floorboards, and back up in to the socket. Obviously if it's concrete that won't work though...

Thanks for your help rebuke.

The floor is constructed from fibreboard sat on a layer of polystyrene. These boards are quite wide and lock together, so it would be quite difficult to lay the cable underneath. Also, I'm not sure if the combined depth of the board and polystyrene would provide the sufficient clearance to bury the cables, I'd probably have to chase them into the concrete underneath - something I want to avoid if possible

 

[rebuke]

Fair enough - concrete floors can be really annoying at times!

There is a safe zone defined as 150mm from the top of the wall, so another option would be to go up, across there, and then back down to the socket (but obviously you'd have to be very careful chasing the drop to the socket, since the original cables are likely already buried there).

Going back to your original plan, a bit of steel conduit (as long as it's earthed by being threaded and attached with appropriate fittings to the backbox at one (or ideally both) sides) would be fine. If you don't want to have to thread conduit etc, then another possibility is to use an appropriate type of cable that has earthed armouring or an earthed metal sheath, e.g. the ali-tube stuff (not sure where you can buy it i'm afraid, i've never tried).

 

[kjm424]

There is a safe zone defined as 150mm from the top of the wall, so another option would be to go up, across there, and then back down to the socket (but obviously you'd have to be very careful chasing the drop to the socket, since the original cables are likely already buried there).

Yeah, after I realised there wasn't the 150mm safe zone along the bottom of the wall (for obvious reason I guess!), I thought about doing it this way. Unfortunately, the room has deep coving - probably about 150mm deep - and I don't fancy messing around with that

If you don't want to have to thread conduit etc, then another possibility is to use an appropriate type of cable that has earthed armouring or an earthed metal sheath, e.g. the ali-tube stuff (not sure where you can buy it i'm afraid, i've never tried).

This is quite an appealing solution. So, using cable with an earthed metal sheath would satisfy 522-06-06? I guess this falls under (i). Maybe something like this: http://www.tlc-direct.co.uk/Products/SW2dot5slash2.html With this type of cable, does the wire armour count as the earth wire for the spur, or would three-core be needed (and connect both the wire armour, and one core to the earth terminals)?

 

[rebuke]

For 2.5mm the armour can be used as the earth, but terminating SWA in to a metal backbox will be 'interesting' to say the least. You'd probably need quite a deep backbox in order for the gland to be buried in the wall properly.

You'd be better off with an ali tube type cable, I think there are ones called flexishield and guardian (but have never used them myself). A quick google reveals http://tpwcc.com/flexishield.html and http://www.batt.co.uk/products/view/306/'Guardian'-XLPE/Ali-Tube/LSZH-600/1000V-'ERA'-Approved

 

[RF Lighting]

I'm not at all convinced with that stuff.

I got sent a sample from the manufacturers, and it looks identicle to pirelli gold FP200