UK Underground Wiring

[Khuz360]

Hi All

I'm looking to run a 10/16mm SWA cable from the main house to the Garage. Currently the power supplied to the garage is with a twin and earth cable in some plastic pipe. The plastic pipe is buried under the conservatory and concrete in the garden areas.


The plastic pipe is of sufficient size that a 10mm cable could in theory be pulled through. Note I did say in theory.

My question is two parts.

1. Is my theory correct in that it is possible to attach the 10mm SWA cable to the existing cable and pull it through.

2. If I were to dig up the concrete garden areas, is it feasible for a domestic sparky to drill through the base of the conservatory roughly 6m long because tearing down the conservatory is an absolute no go.

Thanks

K

 

[Spoon]

It is a possibility! But they so say they need to be on the same circuit - not quite shore how much so, but it may be the magnetic trip coil of MCB/RCBO acts like a choke for the data signals.

In that case you might have to have 13A sockets for the two network thing hung off each end of the 50A-fused SWA, not terribly comfortable about that! Maybe a FCU feeding a 13A socket via a 3A fuse would be fine.

Also not clear how well SWA would carry the signal. If it were in place it would be worth a try, but depending on the decisions over cable routing if you can put in an Ethernet cable it would be far faster and more reliable.

I have one that sends the signal upstairs for the kids. This is on a different circuit to the downstairs.
People have also used them for data to their garage and not had a problem.

 

[pc1966]

I have one that sends the signal upstairs for the kids. This is on a different circuit to the downstairs.
People have also used them for data to their garage and not had a problem.

Worth considering then.

If the OP can live with less power then the option of getting 6mm through the pipe would work, but they need to check the VD over the whole length and to check the supplying fuse (presumably, or MCB) is going to clear OK and the 6mm section is not in danger over being damaged by that.
[automerge]1589631924[/automerge]
20m of 6mm = 20 * 7.9 = 158 mOhm
30m of 10mm = 30 * 4.7 = 141 mOhm
Total = 0.3 Ohm, if acceptable drop 5% = 11.5V limit for current = 38A

Again, assuming 2 core SWA is used, then R1+R2 from Prysmian data sheet:
20m of 6mm = 20 * (3.08 + 7.0) = 202 mOhm
30m of 10mm = 30 * (1.83 + 6.0) = 235 mOhm
Total = 0.44 Ohm, if on TN-S then assume Zs = Ze + (R1 + R2) = 0.8 + 0.44 = 1.24 Ohm which appears to limit the fuse to no more than 32A and that is a bit worrying for selectivity.

Figures obviously should be checked by whoever is responsible for the design, and some of the above could be varied (measured Ze, try 3-core SWA, look at 16+6 options, etc) but it looks like the design is going to be limited to around half the desired power if a 6mm section like that is necessary.
[automerge]1589632523[/automerge]
How about using split concentric if the route is physically protected by the existing pipe? 16mm is around 15 diameter so a sporting chance of getting through.

 

[davesparks]

How about using split concentric if the route is physically protected by the existing pipe? 16mm is around 15 diameter so a sporting chance of getting through.

The existing pipe is MDPE water pipe so is not suitable protection for a buried cable which does not have a complete earthed metallic armour/sheath.
To be used for this purpose only the cable ducts complying with the specified standard in the regulations are allowed.

 

[pc1966]

The existing pipe is MDPE water pipe so is not suitable protection for a buried cable which does not have a complete earthed metallic armour/sheath.
To be used for this purpose only the cable ducts complying with the specified standard in the regulations are allowed.

What is the specific concern here? My understanding is this pipe is concreted in, so water pipe or approved duct pipe, any breaking forces for the concrete is going to go through either of them.

Yes, spilt concentric is not complete earthed metallic sheath, but other than the case of a C1 fault of reversed supply polarity, any accidental penetration of the cable will result in the supply OCPD operating (I guess 60% chance of L-N short, 40% L-E short).
[automerge]1589634242[/automerge]
So it is a major step up from the current T&E routed through!

 

[davesparks]

What is the specific concern here? My understanding is this pipe is concreted in, so water pipe or approved duct pipe, any breaking forces for the concrete is going to go through either of them.

Yes, spilt concentric is not complete earthed metallic sheath, but other than the case of a C1 fault of reversed supply polarity, any accidental penetration of the cable will result in the supply OCPD operating (I guess 60% chance of L-N short, 40% L-E short).
[automerge]1589634242[/automerge]
So it is a major step up from the current T&E routed through!

Firstly, as far as I am concerned, it is non-compliant.
I got the impression from the OP that this pipe is only buried in concrete for part of its run, it passes through concrete and the garden, but I may be wrong.

Being a major step up doesn't negate the requirement to comply with the regulations.

 

[pc1966]

I got the impression from the OP that this pipe is only buried in concrete for part of its run, it passes through concrete and the garden, but I may be wrong.

According to Doncaster cables, their split concentric is described as:

These cables are designed to be installed in air, or for burial in free draining soil conditions

So really the only issue is if they are at risk of physical damage. The presence of dampness, etc, is not a problem (other than waterlogged, I presume). If turn run under the existing house floor, or any sort of duct that is below a soil depth of realistic risk (e.g. under concrete), or are clipped out of harms way they should be fine.

Being a major step up doesn't negate the requirement to comply with the regulations.

Which regulation(s) do you believe it goes against?

 

[Khuz360]

If digging a new trench for a bigger duct (or two ducts) is feasible then you would be best to do that and get the cost and inconvenience over and done with in the one step!

Looking at your options you would not get even CAT-5 network cable and 2-core 6mm SWA down a 20mm ID pipe, but if you put in a new large duct you can do as you please.

If you are unsure of future demands then it is probably worth just going for 16mm cable instead of triming expectation to use 10mm. It will add a bit of cost at the start but probably no more than £50-100, and is far cheaper than finding you need more capacity later.

Same as the networking, your best solution would be a switch at the out building to have as many ports as you want, but running through at least 2 feed cables means you can deal with a fault on one (or even just swap to compare) without having any more work.

In duct you don't need SWA network cable (unless mice, etc, are potential visitors in an unsealed pipe) but you should use outdoor rated cable for the humidity resistance, etc.

To be honest If I'm digging and moling or drilling new holes, then I will increase the cable size to 16mm.

The network side of things would have been one outdoor rated cable if it went through the existing pipe, but since I know that isn't possible. The network cable is on the back burner unless I dig up.

If I dig up then I would be running double cables into switches at both ends most likely CAT6a or CAT7 to future proof.

Have you considered using a powerlink for the data?
Somethink like this.

https://cpc.farnell.com/tp-link/tl-pa7017-kit/av1000-gigabit-powerline-starter/dp/CS33256?st=tp%20link%20powerlink

It is a possibility! But they so say they need to be on the same circuit - not quite shore how much so, but it may be the magnetic trip coil of MCB/RCBO acts like a choke for the data signals.

In that case you might have to have 13A sockets for the two network thing hung off each end of the 50A-fused SWA, not terribly comfortable about that! Maybe a FCU feeding a 13A socket via a 3A fuse would be fine.

Also not clear how well SWA would carry the signal. If it were in place it would be worth a try, but depending on the decisions over cable routing if you can put in an Ethernet cable it would be far faster and more reliable.

I have one that sends the signal upstairs for the kids. This is on a different circuit to the downstairs.
People have also used them for data to their garage and not had a problem.

Worth considering then.

If the OP can live with less power then the option of getting 6mm through the pipe would work, but they need to check the VD over the whole length and to check the supplying fuse (presumably, or MCB) is going to clear OK and the 6mm section is not in danger over being damaged by that.
[automerge]1589631924[/automerge]
20m of 6mm = 20 * 7.9 = 158 mOhm
30m of 10mm = 30 * 4.7 = 141 mOhm
Total = 0.3 Ohm, if acceptable drop 5% = 11.5V limit for current = 38A

Again, assuming 2 core SWA is used, then R1+R2 from Prysmian data sheet:
20m of 6mm = 20 * (3.08 + 7.0) = 202 mOhm
30m of 10mm = 30 * (1.83 + 6.0) = 235 mOhm
Total = 0.44 Ohm, if on TN-S then assume Zs = Ze + (R1 + R2) = 0.8 + 0.44 = 1.24 Ohm which appears to limit the fuse to no more than 32A and that is a bit worrying for selectivity.

Figures obviously should be checked by whoever is responsible for the design, and some of the above could be varied (measured Ze, try 3-core SWA, look at 16+6 options, etc) but it looks like the design is going to be limited to around half the desired power if a 6mm section like that is necessary.
[automerge]1589632523[/automerge]
How about using split concentric if the route is physically protected by the existing pipe? 16mm is around 15 diameter so a sporting chance of getting through.

Power line adaptors are a non-starter. The lack of reliability and poor performance, makes them frustrating at best and at worst will lead to a very destructive meeting with a big mf hammer.

The existing pipe is MDPE water pipe so is not suitable protection for a buried cable which does not have a complete earthed metallic armour/sheath.
To be used for this purpose only the cable ducts complying with the specified standard in the regulations are allowed.

Firstly, as far as I am concerned, it is non-compliant.
I got the impression from the OP that this pipe is only buried in concrete for part of its run, it passes through concrete and the garden, but I may be wrong.

Being a major step up doesn't negate the requirement to comply with the regulations.

According to Doncaster cables, their split concentric is described as:

These cables are designed to be installed in air, or for burial in free draining soil conditions

So really the only issue is if they are at risk of physical damage. The presence of dampness, etc, is not a problem (other than waterlogged, I presume). If turn run under the existing house floor, or any sort of duct that is below a soil depth of realistic risk (e.g. under concrete), or are clipped out of harms way they should be fine.


Which regulation(s) do you believe it goes against?

Davesparks, you are correct in your assumption about the MDPE. The pipe goes into the house, and the cable then runs under the floorboards of the house a few metres (10 - 15) to the fuse board which will be updated. The breaker will be effectively a sub main to the garage at the appropritate amperage.

I don't know what split concentric is. I can live with less power if the cost of drilling is too prohibitive.

Thank you to everyone who is contributing to this question.

 

[pc1966]

A check on cost shows it is not the cheapest option, but if cost of replacing pipe is included it might be worth considering:

PVC Insulated Split Concentric Cables (Per Metre)

PVC insulated split concentric cables is available in a selection of sizes ranging from 16mm² to 25mm². Key Features Five cable size available options:- 16mm²- 25mm² Conductor- Phase - Plain Annealed Copper Class 2 Stranded to BSEN60228- Neutral - Plain Annealed Copper Class 1 Solid to...

www.expertelectrical.co.uk

[automerge]1589663803[/automerge]
Data sheet:

http://www.doncastercables.com/uploads/SPLIT_CONCENTRIC_Datasheet.pdf

[automerge]1589664832[/automerge]

Power line adaptors are a non-starter. The lack of reliability and poor performance, makes them frustrating at best and at worst will lead to a very destructive meeting with a big mf hammer.

That is my view of them...

I don't know what split concentric is. I can live with less power if the cost of drilling is too prohibitive.

The "split concentric" cable is what the DNO uses to power you property (most likely). If you look at the Doncaster data sheet you will see what it is like.

It quite likely possible that @davesparks is right and it is not OK due to a specific wiring regulation, but so far I don't see any justifiable reason for not using it here.
[automerge]1589665181[/automerge]
The names comes from the construction where the centre is the live/phase conductor, and around that are concentric wires, and here they are "split" with a few earth and a few more insulated neutral. The N+insulation conductors have the same diameter as bare E, but they add up to essentially the same CAS as the live.

 

[freddo]

Split con is a great cable, it is so much lighter and more flexible than the SWA, the OD is very small compared to the same conductor CSA of SWA.

 

[pirate]

I used powerline adaptors for years in my last house and never had any problems. They weren't even very "fast" ones, but fine for streaming TV and general internet use. The ones i had are discontinued now, superseded by faster units, and i have fibre here, so if anyone wants maybe 4 or 5 of these "old" ones, let me know!

 

[davesparks]

The "split concentric" cable is what the DNO uses to power you property (most likely). If you look at the Doncaster data sheet you will see what it is like.

I would say it is the least likely to be used to supply a house, it is only used for new/altered TNS services which are rare these days.
Almost all new supplies will be TNCS using concentric cable, older supplies are likely to be one of a variety of paper insulated lead sheathed cables.
[automerge]1589726305[/automerge]

According to Doncaster cables, their split concentric is described as:

These cables are designed to be installed in air, or for burial in free draining soil conditions

So really the only issue is if they are at risk of physical damage. The presence of dampness, etc, is not a problem (other than waterlogged, I presume). If turn run under the existing house floor, or any sort of duct that is below a soil depth of realistic risk (e.g. under concrete), or are clipped out of harms way they should be fine.


Which regulation(s) do you believe it goes against?

I don't doubt that is what Doncaster cables say, but then they aren't concerned with compliance with BS7671 specifically, they make the cable to its relevant standards and it is up to the specifier/installer to decide what is, or is not, compliant with the regulations they are working to.

Split concentric is suitable for direct burial from a physical point of view, and it is approved for such use by DNO's and the regulations they work to.

However in an installation complying with BS7671 then regulation 522.8.10 prevents its use for direct burial.
Under that regulation cables not protected by suitable duct or conduit must incorporate an earthed armour or metal sheath which is suitable for use as a protective conductor.
Split concentric has neither an earthed armour nor metal sheath.

If it is to be installed in ducting then the ducting must provide equivalent mechanical protection to an earthed armour or metal sheath.
BS EN 61386-24 is the standard for underground conduits.

 

[Khuz360]

So I got in touch with a local company who do Moling and got a ballpark figure which is an eye watering £1400 - £2000 unfortunately. Add the cost of excavation and printed concrete, I'm at £8k before any electrical work is even undertaken, which is way out of budget.

That leaves me with 2 options:

Option 1: Use a 6mm SWA cable thread through the MDPE Pipe and ensure I keep the load below the maximum level.

Option 2: Keep the existing wire and add a proper consumer unit with breakers with a view to upgrade the cable in the future when budget allows.

What would be the concerns with option 2?

 

[Spoon]

Option 1: Use a 6mm SWA cable thread through the MDPE Pipe and ensure I keep the load below the maximum level.

Do you know what the max level is?
Looking at 45 meters then its about 20A. About 4.6kW which is a lot less that your 13kW you originally said.
Your max Volt Drop is now 3%, as you have lighting.

Option 2: Keep the existing wire and add a proper consumer unit with breakers with a view to upgrade the cable in the future when budget allows.

What is the existing cable size? Have I messed this, as I can't see it?

 

[Khuz360]

Do you know what the max level is?
Looking at 45 meters then its about 20A. About 4.6kW which is a lot less that your 13kW you originally said.
Your max Volt Drop is now 3%, as you have lighting.



What is the existing cable size? Have I messed this, as I can't see it?

I'd have no choice but to keep it below the 4.6kw, which means not getting the machines I originally wanted to and going for considerably less powerful ones which is frustrating however necessary.

I have no idea what size cable the existing wire actually is, only that it is twin and earth. At best it's 4mm at worst it's 2.5mm. Installed over 20 years ago.

Essentially I'm asking is it possible for a spark to come out and simply upgrade the fuse box to a consumer unit in the garage, add a few outlets and the put in the lights. Or do the regs require them to replace the in feed because it's unlikely it's going to be sufficient size.

 

[Spoon]

Essentially I'm asking is it possible for a spark to come out and simply upgrade the fuse box to a consumer unit in the garage, add a few outlets and the put in the lights. Or do the regs require them to replace the in feed because it's unlikely it's going to be sufficient size.

You say that the existing cable is wired back to your consumer unit.
Does it wire back to it's own breaker? (I'm presuming it is but it's not good to presume everything) If not then what circuit does it wire back to?
What size is the breaker?
Why add a consumer unit in the garage now?
I'm presuming the 'fuse box' which is in the garage, is a fused spur? (See.... presuming things again)
Why not stick with the fused spur until you upgrade the cable to the garage?