Cat 6 cable and mains wiring. (1 Viewer)

[DBK]

Not MH orientated but electronics so I am putting this question here in case any wiring experts can help.

I am tidying up the wiring to a TV by putting the cables behind the plasterboard. There will be one 3 gang little socket carrying the coax signal, an HDMI socket and an Ethernet socket. There will then be another socket for the 13A mains.

I only have to run the cables a maximum of about 2m horizontally to where the router and blu-ray player will sit and it will save me quite a bit of plastering if I can hide them all in a single run. The plan is to cut slots over the vertical wooden battens behind the plasterboard and "fish" the cable to the next batten. This should only leave me with about 3 short slots to plaster over afterwards.

My question is will having the mains and the Ethernet cable, which is Cat 6 be a problem over such a relatively short distance if they are close together?

I have read you should keep them at least 300mm apart and if they have to cross they should do at right angles. The Cat 6 cable is unshielded.

I suspect I am just being lazyand need to cut separate channels for the mains but if anyone has any experience of this I would be grateful for advice.

 

[canopus]

Golden rule don't run mains and comms cables in close proximity. :thumb:

 

[Techno]

It will be fine
I've run mains and data all over on seperate trays and then when it gets to the desks or dado trunking it's all in plastic two or three compartement trunking with no metal fillet. I've never know a data man complain yet.

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[scotjimland]

The golden rule is to run mains and coms. in separate ducts, .. however,

I've done a similar run to my TV using about 6ft of mini trunking. Mains, LAN , HDMI, TV aerial, and a USB cable and had no problems..

 

[sdc77]

Can't imagine you'll have any probs over that distance. Main probs are good termination of your cat 6 cable and avoiding sharp bends.

 

[TheBig1]

you will only pick up data noise if the mains cabling is badly connected or damaged. in reality any network card is capable of being affected by mains hum but they filter it out. what you want to really avoid is running a data cable close to a transformer

what you are suggesting should be fine... been doing similar for years without issues

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[DBK]

Many thanks for the input. Just put the 13A cable in and it was a lot easier than I expected. So if the men's curling team can only manage silver (as it looks but fingers crossed) I'm going for gold and will separate them. This should give me more holes to fill but hopefully they will be smaller holes!

Will post picture of my butchery later for your amusement.

 

[Ed Excel]

The issue of separation of structured wiring cabling and low voltage cables is more about safety than performance. You need to keep them a reasonable distance apart to avoid accidents happening in the future to some unsuspecting DIYer/tradesman. 230V on your CAT6 cable would be dangerous. Separation will have a double benefit in that interference on your data cabling should, also, not be a problem, although, CAT6 cable is layed up (twisted) to avoid the conductors running parallel with others.

PS glad to see you are going to separate them.

 

[cmcardle75]

Not MH orientated but electronics so I am putting this question here in case any wiring experts can help.

I am tidying up the wiring to a TV by putting the cables behind the plasterboard. There will be one 3 gang little socket carrying the coax signal, an HDMI socket and an Ethernet socket. There will then be another socket for the 13A mains.

I only have to run the cables a maximum of about 2m horizontally to where the router and blu-ray player will sit and it will save me quite a bit of plastering if I can hide them all in a single run. The plan is to cut slots over the vertical wooden battens behind the plasterboard and "fish" the cable to the next batten. This should only leave me with about 3 short slots to plaster over afterwards.

My question is will having the mains and the Ethernet cable, which is Cat 6 be a problem over such a relatively short distance if they are close together?

I have read you should keep them at least 300mm apart and if they have to cross they should do at right angles. The Cat 6 cable is unshielded.

I suspect I am just being lazyand need to cut separate channels for the mains but if anyone has any experience of this I would be grateful for advice.

It will work fine electrically. The frequency is so low on the mains cable that it will not interfere with the UHF signals on the network cable.

However, it is not permitted for safety reasons. You must have two insulation resistant sheaves between the conductors. The mains cable will have one, but your Cat 6 will not count, as the outer layer is too thin. You could run the mains cable (or the network cable) in conduit to solve the problem.

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[DBK]

Again, many thanks, I hadn't really considered the safety aspect but having once but a masonry drill through a 30A cooker feed (spectacular!) I can see the point. I remember years ago when I was serving in Belize the lights of our mess bar were forever flickering but no one really bothered as a thump on the bar usually worked. That the building was made of wood with a thatched roof never entered the discussions. A few days before I left they did some renovation and prising off a plywood panel in the bar they found the mummified remains of a rat - with its teeth wrapped around the mains cable. It would be nice to think it is still there in a glass case behind the bar but I suspect it was binned.

Today, with one ear tuned into the curling (hard to argue with the result) I have finished most of the preparatory work. The picture below shows what it looks like at the TV end, which is hidden behind the dog blanket. There are 3 slots in total for each cable over the vertical battens behind the plaster board. The smaller square opening will hold the low voltage stuff and the lower one will be for a twin 13A socket. They are about a foot apart. I haven't added a second layer of insulation as recommended and will plead ignorance if the house burns down. I think the risk is low as the current(!) family plans are we will stay here until carried out feet first so what subsequent owners get up to is their problem.

The top run has the co-ax in and the bottom run has the 13A ring main threaded. I need to add the Cat6 Ethernet cable and the HDMI cable to the top run. The HDMI is going to be fun. I have ordered some HDMI sockets but you don't seem to be able to buy bare HDMI cable so I will cut the ends off an existing cable and hopefully can connect that to the sockets. HDMI seems to be a bit of a mish-mash, four twisted pairs and seven additional separate conductors, fifteen wires in total. If all else fails I will just pull a standard HDMI cable with plugs on the ends through and have the ends waving around as tails, so to speak.

Anyway, the main point of this long-winded post is to extol the virtues of a magical tool which I had heard about but have never used.

You will see in the picture below the lower holes have ragged edges. These were done by hand with a pad saw. This worked fine but I was then lent an oscillating saw - one of these Broken Link Removed

It quickly produced fine cuts in the plaster with very neat edges. I also used it to cut into the battens so I can chisel them out tomorrow to give more space for the three cables. It doesn't produce much dust, a fraction of what an angle grinder would make, although it does get into the air a bit so covering things up is advised.

If I ever need to cut holes in plaster board again I might buy one, ScrewFix sell cheapies which are good enough for light use I am told but the blades, whatever saw you have, are not cheap. Hit a screw at your peril - I was lucky today and can hand it back undamaged. The lower picture is of the tool itself - note some dust but not too much.

Apologies for the large images.


BROKEN LINK


BROKEN LINK

 

[Ed Excel]

Neat job. I see you only have one power cable which I assume you are spurring off an existing socket on a ring-main circuit. I don't imagine you will want to use the dual socket you are installing to its full capacity, but wiring in this manner limits the load to 13A; Connect more and you will overload your cable. Again, you now know this, but others won't. If you have spurred off the ring with a 13A connection unit, forget the above.

Like the oscillating saw!

 

[Techno]

Does not need a fused spur. On site guide appendix 8.2.4 allows a twin socked outlet unfused.

BTW 2.5 T&E is rated at 27amps and for a short spur it will easily carry the ring circuit mcb rating of 30/32amps

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[Ed Excel]

Does not need a fused spur. On site guide appendix 8.2.4 allows a twin socked outlet unfused.

BTW 2.5 T&E is rated at 27amps and for a short spur it will easily carry the ring circuit mcb rating of 30/32amps

Surely your figures demonstrate it will not carry the load you suggest. Also, it will carry less when derating factors are applied.

 

[Techno]

No they don't if you read it carefully. As I said it is permitted by BS 7671
Also the most you can draw from a twin socket is 26 amps

 

[Ed Excel]

Still not sure 2.5, derated, would be sufficient. I would use 4.0sq mm in this instance. BS7671 is a basis for engineering designs not an installation manual.

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[Techno]

Derated for what? I've never in 40 years met a derated ring main

 

[Techno]

Of course if in doubt? ask an electrician :thumb:

 

[geo glasgow]

before running in wall conmnect everything up

the way it would be when completed switch all of your products and sources on
switc your hdmi switch or sources over and use the various hdmi on tv screen
does the system put out video or audio interference ,
yes? the screen power and video separate iv never needed to but separate first to see if it then works perfect ,
NO? WORKS perfect then your good to go,, remember you can screen all cables if required, foil. or cable management trunking again over this lenth im sure all work work great,, . good luck any issues let me know i can assist you
but would need to know all sources your using,,:thumb:

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[daveandsan]

Excuse my ignorance but i didn't think anyone but a qualified electrician was allowed to put spurs in now under the new regulations. I wouldnt think your insurance would be very happy if something untoward was to happen.

 

[Techno]

A spur is permitted by a competent person, it does not have to be an electrician. A test certificate would be useful :thumb:

 

[Techno]

My lad posted this on facebook today and I had to laugh
Broken Link Removed

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[Ed Excel]

Derated for what? I've never in 40 years met a derated ring main

I don't think the discussion was about RFC cabling. If you look at DBK's images you'll see he's installing the cable in thermal insulation. Surely you would derate any cable installed in this manner?

Also, the standard suggests the cable used should be capable of carrying the current rating of the circuit protective device. You already confirmed 2.5sq mm is not.

As an aside, you may not have experienced derated RFC cabling in the type of installations you've worked on, but it is acceptable in the standard in certain situations.

 

[Techno]

No you would not "derate" a ring main because of thermal insulation in a house. The thermal insulation will be at the same ambient temperature as the house and everytyhing in it including cables in plastered walls and lofts etc.
Again I'm quoting from the IEE regs ONSITE guide and experience with regard to a spur

 

[Ed Excel]

No you would not "derate" a ring main because of thermal insulation in a house. The thermal insulation will be at the same ambient temperature as the house and everytyhing in it including cables in plastered walls and lofts etc.
Again I'm quoting from the IEE regs ONSITE guide and experience with regard to a spur

I don't think we are talking about the same thing Andy. The cabling in point is for a spur, not the RFC, and that cable needs to be adequate for the circuit protection provided, to be compliant with the standard. You quoted 27A for 2.5sq mm. With a breaker of 32A, how many amps fault current, not load, would you think could start a fire, before the device tripped. Along with a reduction in current carrying capacity, because of it running in thermal insulation. I don't consider 2.5 is big enough.

As for the thermal insulation, it is not the temperature of the material that matters, it's the fact that heat produced by current flow in the cable cannot escape.

Please don't take BS7671 as gospel. As I said previously, it is a design 'guide', coincidentally, also the terminology used for the Onsite books you refer to. The standard is a guide to electrical installation design and states that alternative arrangements are acceptable so long as they are designed by a qualified engineer, something I've been doing for 46 years.

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[cmcardle75]

I don't think we are talking about the same thing Andy. The cabling in point is for a spur, not the RFC, and that cable needs to be adequate for the circuit protection provided, to be compliant with the standard. You quoted 27A for 2.5sq mm. With a breaker of 32A, how many amps fault current, not load, would you think could start a fire, before the device tripped. Along with a reduction in current carrying capacity, because of it running in thermal insulation. I don't consider 2.5 is big enough.

As for the thermal insulation, it is not the temperature of the material that matters, it's the fact that heat produced by current flow in the cable cannot escape.

Please don't take BS7671 as gospel. As I said previously, it is a design 'guide', coincidentally, also the terminology used for the Onsite books you refer to. The standard is a guide to electrical installation design and states that alternative arrangements are acceptable so long as they are designed by a qualified engineer, something I've been doing for 46 years.

It was my understanding (I might be wrong) that you can allow 20A for a double 13A socket. Also, I'm not sure this installation would count as buried in insulation, as the cable runs between the plasterboard and the insulation.

 

[pappajohn]

what height are the new cables David ?
To remain within the regulations the max height for mains cables is 150mm above a floor, to either vertical side of a wall corner, below a ceiling or horizontally and vertically from a switch or socket.

The diagram shows DO NOT DRILL zones as there may be wiring.

In reality all wiring should either go up or down within the width of the accessory

 

[Ed Excel]

It was my understanding (I might be wrong) that you can allow 20A for a double 13A socket. Also, I'm not sure this installation would count as buried in insulation, as the cable runs between the plasterboard and the insulation.

You're quoting a current for a load estimate there, not fault current. 2.5 sq mm can carry 27A, as I think everyone knows now, but it's not capable of carrying more such as in a fault situation.

I'm afraid It does count as buried, just as it counts in a loft when thermal insulation is layed on top of cabling and there is plasterboard below.

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[Ed Excel]

what height are the new cables David ?
To remain within the regulations the max height for mains cables is 150mm above a floor, to either vertical side of a wall corner, below a ceiling or horizontally and vertically from a switch or socket.

The diagram shows DO NOT DRILL zones as there may be wiring.

In reality all wiring should either go up or down within the width of the accessory

Good point PJ, a whole area we haven't even mentioned yet. In the same vein, the timber wall battens should be drilled, as with a new installation. I think I would just cap the slots DBK has cut, like we used to do with floor joists.

 

[DBK]

Interesting stuff here. I will ponder what has been written and makes changes if necessary. Doubling up the 2.5 mm sq cable to the socket seems a safe and easy thing to do.

It's odd that what was considered perfectly safe a few years ago is now prohibited. We are moving an oil tank in the garden at the moment and where it was before would not now be permitted, even though it was installed just 10 years ago - too close to the boundary and no 600 mm wide walkway around it.

 

[Techno]

The regs are clear second paragraph.
That cable will not even get warm never mind hot. A sledgehammer to crack a nut me thinks.

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