Meter Tails in Cavity - Horizontal Run

[EvilDrPorkChop]

We've just recently bought a property which is around 25 years old and will be completing some alterations. The consumer unit is in the Utility high up on the wall. Isn't in the ideal place and we'd like to move it, due to a new kitchen layout.

On further investigation the meter tails run up the cavity to the consumer unit (I can see from the outside meter cupboard)

After a bit of research online I see this is a bit of a grey area. We'd like to keep the consumer unit in the same vicinity but move it horizontally across the wall by about 1m and down the wall so it's lower down (More or less the same height as the meter box outside) In affect the meter tails would be running horizontally across the cavity instead of vertically, but within the 3m rule I have seen about the tails.

Is this allowed? We'd get an electrician out to look but current situation we can't and are trying to plan ahead.

 

[pc1966]

If the run is under 3m and the cables are adequately protected from the risk of damage then moving the CU to such a position is not any harder than the effort of extending the various circuits to the new location (assuming it is not a complete rewire).

Otherwise you can have more than 3m if there is a fused switch at the meter end to protect the cable from overload (as you are not supposed to depend on the supplier's cut-out for for that, even if it probably would do the job).

So again it is perfectly possible to do well over 3m but it adds to the cost for the fused switch and the long high-current cable. Normally you would look at armoured wire for long runs and/or if you have no trunking or similar for cable protection. You would need to get a couple of quotes for the job but I would not expect it to add greatly even if you did need that.

 

[DPG]

I dislike meter tails running in the cavity, especially horizontally. They bridge the cavity gap and they are just waiting for some one to drill through them to fit an outside socket, etc

 

[pc1966]

Could you run SWA cable horizontally outside and then through the wall to avoid a hidden unsupported horizontal run?
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For info, 25mm 2-core SWA is around 22mm diameter and usually the minimum bend radius is 8 times the diameter so around 18cm. that would have to be factored in to the drilling/channel-cut for such a run.

 

[westward10]

It's fine don't worry about it. The supply is existing and all you are doing is shortening it not replacing.

 

[EvilDrPorkChop]

Firstly, thanks for all the replies.

I dislike meter tails running in the cavity, especially horizontally. They bridge the cavity gap and they are just waiting for some one to drill through them to fit an outside socket, etc

I did think this and it's not ideal, however it as they are currently. When I opened the meter box initially there's a hole in the bottom where the main electric supply coming into the house is running up the cavity too which didn't appear right - so that's in the cavity too towards the bottom!
In reality moving the consumer unit is bring it closer, and it'll probably be within 0.5m.

Could you run SWA cable horizontally outside and then through the wall to avoid a hidden unsupported horizontal run?

For info, 25mm 2-core SWA is around 22mm diameter and usually the minimum bend radius is 8 times the diameter so around 18cm. that would have to be factored in to the drilling/channel-cut for such a run.

Didn't want anything external if possible as it's on show at the front of the property. If that were the case i'd leave the consumer unit where it is currently before that.

Getting the cables without bending too much shouldn't be an issue. As most of the property is being ripped apart we can create some larger holes to get the wires in a patch up later.

What would be classed as supported run, something like running the cables through a solid plastic tubing? Just thinking if it's even physically doable

 

[pc1966]

Didn't want anything external if possible as it's on show at the front of the property. If that were the case i'd leave the consumer unit where it is currently before that.

Getting the cables without bending too much shouldn't be an issue. As most of the property is being ripped apart we can create some larger holes to get the wires in a patch up later.

Could you take SWA in at the existing meter box and then run it horizontally in the cavity?

If the wall is open inside for other work then you could have it supported as needed (cleats to fix to the wall if not enough support from any drilled beams, etc) and at least it provides some good protection against accidental drilling or other damage in the future.

While there is not much specifically given in the wiring regulations about support, in the IET Guidance Note 1 (Table G1) the figures for non-armoured cable of 9-15mm diameter (covering typical meter tail cables that are 11mm or so) have the recommended maximum spacing for horizontal fixing as 300mm, while for armoured wire of 20-40mm (typical case for 25mm2 SWA here) it is 450mm max.

What would be classed as supported run, something like running the cables through a solid plastic tubing? Just thinking if it's even physically doable

In terms of support then yes you could use plastic pipe, also you could use metal pipe (i.e. conduit), or metal trunking, both of which would need to be earthed but would serve a similar purpose to SWA in terms of reducing the risk in the event of drilling (as well as being basically non-flammable in the first place).

A final factor is the type of earthing the property has:

• If, as is most likely it is TN-S or TN-C-S (i.e. earth wire from the supplier's cut-out) then earthing the SWA armour or metal trunking is simple.
• If it is a TT earth (separate earth rod driven in the garden, etc) then you would need an RCD in the meter box as the cables coming in and related physical protection would be part of the installation and need protection from an earth fault.

 

[Midwest]

I dislike meter tails running in the cavity, especially horizontally. They bridge the cavity gap and they are just waiting for some one to drill through them to fit an outside socket, etc

I agree, although it sounds in the OP’s, the new tails will only run in the cavity for less than 0.5m?

The other issue with running cables in cavities, is they can be damaged dragging over metal cavity ties, which may be unseen. Unless they can be installed in some protective ducting.

Could not the horizontal part be run inside, cover in plastic trunking, or if thats not possible, in a chase covered with suitable metal (3mm or more thick) to protect them.

 

[pc1966]

Just to add, if it is TN-C-S you would need to use 3 core SWA as I don't think the 25mm 2-core armour is going to meet the 16mm copper equivalent for the earth.

 

[Wilko]

Hi - have you actually seen the tails travelling in the cavity? I ask this because a lot of times they’ve actually been put all the way through onto the internal block work surface and then travel up to the CU under the dot and dab etc. If so, this means the run is less than 50mm deep and perhaps needs further attention. Can you have a careful look?

 

[westward10]

Do the tails actually need replacing just shorten the old ones.

 

[EvilDrPorkChop]

Hi - have you actually seen the tails travelling in the cavity? I ask this because a lot of times they’ve actually been put all the way through onto the internal block work surface and then travel up to the CU under the dot and dab etc. If so, this means the run is less than 50mm deep and perhaps needs further attentionView attachment 57381. Can you have a careful look?

Yes I think looking from the meter box externally they probably are running in the cavity.

Do the tails actually need replacing just shorten the old ones.

I don't know is the honest answer. Seeming i'll be having a new consumer unit and re routing them anyway i'd think it'd be advisable to replace them anyway? They're probably from when the house was built so 25+ years

if thats not possible, in a chase covered with suitable metal (3mm or more thick) to protect them.

Yes I guess this is the other option. Would the metal have to be earthed? - Just thinking about having concealed wiring connections in the wall and future access.

 

[westward10]

25+ years they are probably fine.

 

[Midwest]

Yes I guess this is the other option. Would the metal have to be earthed? - Just thinking about having concealed wiring connections in the wall and future access.

No; can’t find a link for the stuff. Sure someone will have, think @Leesparkykent has before.

PS you shouldn’t need to have any ‘connections’.

 

[Leesparkykent]

No; can’t find a link for the stuff. Sure someone will have, think @Leesparkykent has before.

PS you shouldn’t need to have any ‘connections’.

PRODUCTS | TridentSections - http://www.tridentsections.co.uk/press/products/ eddies/electric centre order it in.

 

[pc1966]

As Midwest already said you should not have any connections behind the cable protector!

Certainly I would earth it. It might not be necessary in the sense that if it is plastered in and cannot be touched it is no longer an "exposed conductive part" but I would prefer in the event of some muppet drilling though and hitting the tails it would cause a bang and DNO fuse blow rather than someone dying.

 

[Ian1981]

As Midwest already said you should not have any connections behind the cable protector!

Certainly I would earth it. It might not be necessary in the sense that if it is plastered in and cannot be touched it is no longer an "exposed conductive part" but I would prefer in the event of some muppet drilling though and hitting the tails it would cause a bang and DNO fuse blow rather than someone dying.

How would you make the earthing connection accessible for inspection and testing? And as it’s mechanical protection it’s not actually an exposed conductive part as it does not form part of the electrical installation.
It’s not necessary when using mechanical protection as the idea is that you cannot penetrate the cables. Always a contentious matter regarding what can and can’t be used.

 

[pc1966]

How would you make the earthing connection accessible for inspection and testing? And as it’s mechanical protection it’s not actually an exposed conductive part as it does not form part of the electrical installation.
It’s not necessary when using mechanical protection as the idea is that you cannot penetrate the cables. Always a contentious matter regarding what can and can’t be used.

I guess you could have one bond wire top and one bottom, then a resistance check between the two earth wires would show both connections are electrically good. OK, might not satisfy the inspection part for physical soundness!

I guess it also depends in part of the cover is exposed inside a box covering the CU, etc. But you have a point.

 

[Ian1981]

I guess you could have one bond wire top and one bottom, then a resistance check between the two earth wires would show both connections are electrically good. OK, might not satisfy the inspection part for physical soundness!

I guess it also depends in part of the cover is exposed inside a box covering the CU, etc. But you have a point.

I suppose you could solder,weld or braze it on, that would meet requirements but it’s a faff about.

 

[pc1966]

Crimp ring terminal and a bolt with nylock nut?

Soldering to that size of metal would be very hard with most "electrical" sized iron, more a blow lamp job!