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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
 
Does the existing cable move in the duct? If not, then you probably won't draw through a new cable on it.

Are you asking if someone could drill through the conservatory laterally? With a 6 metre long drill bit?! Unlikely!

Could possibly mole it, but it won't be cost effective. You'd need to speak with an expert that does this though.
 
Of the existing cable is free to move in the pipe then yes if the pipe is large enough you can pull another cable in to replace it.
I would probably use the existing cable to pull a rope into the pipe, then pull a balled up rag through it to clean out any crap that's got into it.
If its a tight fit maybe pull a rag soaked in cable pulling lube through to coat the pipe in slippery stuff.


Drilling a 6m long hole is possible for a specialist contractor, but that might cost more than knocking down the conservatory and rebuilding it.

If you can pull the whole way though the existing pipe then you might be able to dig down to it where it goes under the conservatory and just pull through the section under there.
 
Trying on the shortest length of pipe that is reasonable is your best plan - following davesparks advice, etc. Is only the sub-conservatory bit that really needs puling through, can you get to both ends easily enough?

Otherwise is there an alternate route that the cable could take? Having an extra 10m of so of SWA to route round something is going to be a lot cheaper than getting a specialist to bore under the conservatory!

If you do have a long route though you might want to check the cable size calculations relative toy your expected load before starting.
 
Does the existing cable move in the duct? If not, then you probably won't draw through a new cable on it.

Are you asking if someone could drill through the conservatory laterally? With a 6 metre long drill bit?! Unlikely!

Could possibly mole it, but it won't be cost effective. You'd need to speak with an expert that does this though.

The duct has an outer diameter of 25mm. I believe it MDPE pipe which if the standards are uniform the inner diameter should be around 20mm. The outer diameter of 10mm Armoured cable would be around 19mm I think (correct me if I'm wrong). So in theory should work.

I was thinking it would need to be moled through. Evidently this is going to be an expensive option :(.

Of the existing cable is free to move in the pipe then yes if the pipe is large enough you can pull another cable in to replace it.
I would probably use the existing cable to pull a rope into the pipe, then pull a balled up rag through it to clean out any crap that's got into it.
If its a tight fit maybe pull a rag soaked in cable pulling lube through to coat the pipe in slippery stuff.


Drilling a 6m long hole is possible for a specialist contractor, but that might cost more than knocking down the conservatory and rebuilding it.

If you can pull the whole way though the existing pipe then you might be able to dig down to it where it goes under the conservatory and just pull through the section under there.

Thanks for the guidance.

If I were to dig down then it would be to run two sets of cable (power and data). Is there a ball park figure that I'd be looking at for mole drilling?

Trying on the shortest length of pipe that is reasonable is your best plan - following davesparks advice, etc. Is only the sub-conservatory bit that really needs puling through, can you get to both ends easily enough?

Otherwise is there an alternate route that the cable could take? Having an extra 10m of so of SWA to route round something is going to be a lot cheaper than getting a specialist to bore under the conservatory!

If you do have a long route though you might want to check the cable size calculations relative toy your expected load before starting.

If I were to dig up the concrete garden area, the conservatory bit would be in the middle. The only reason I'm considering digging up the garden area would be to run two sets of cable.

Already checked the cable size requirements, according to the calculator I used, 10mm would be more than enough for the run, based on a load of 13kw with an allowable voltage drop of 5% going across 50m of cable. 16mm would be better, but that won't fit through the existing Pipe.
 
The duct has an outer diameter of 25mm. I believe it MDPE pipe which if the standards are uniform the inner diameter should be around 20mm. The outer diameter of 10mm Armoured cable would be around 19mm I think (correct me if I'm wrong). So in theory should work.

Already checked the cable size requirements, according to the calculator I used, 10mm would be more than enough for the run, based on a load of 13kw with an allowable voltage drop of 5% going across 50m of cable. 16mm would be better, but that won't fit through the existing Pipe.

No way will you get 10mm SWA down a 25mm MDPE pipe over anything other than a short distance, the friction in the pipe will be too much. Plus the slightest bend in the cable as it goes in will get stuck.

Volatge drop should be worked out from the intake to the furthest point, not for just this circuit.
If this circuit then feeds any lighting the voltage drop limit is 3% from the intake to the end of the lighting circuit.
Likewise for power circuits it's 5% for the whole run from intake to the furthest point.
 
Already checked the cable size requirements, according to the calculator I used, 10mm would be more than enough for the run, based on a load of 13kw with an allowable voltage drop of 5% going across 50m of cable. 16mm would be better, but that won't fit through the existing Pipe.

What calculator did you use?
13kW = 56.52A @ 230V
Breaker size = 60A
Volt drop over 50m for 10mm 70° SWA cable = 13.2V = 5.74%
 
If I were to dig up the concrete garden area, the conservatory bit would be in the middle. The only reason I'm considering digging up the garden area would be to run two sets of cable.
Do you have to bury it, could you run if over the conservatory?

If you need two cables then I really think you need bigger trunking...
 
No way will you get 10mm SWA down a 25mm MDPE pipe over anything other than a short distance, the friction in the pipe will be too much. Plus the slightest bend in the cable as it goes in will get stuck.

Volatge drop should be worked out from the intake to the furthest point, not for just this circuit.
If this circuit then feeds any lighting the voltage drop limit is 3% from the intake to the end of the lighting circuit.
Likewise for power circuits it's 5% for the whole run from intake to the furthest point.

Define short distance. The actual run of cable in the Pipe is no more than 20m.

I was afraid of that. It may have to drop down to 6mm then.

Sorry I don't understand what you mean, when it comes to Voltage Drop. My assumption is as follows:

The SWA cable is coming from the main consumer unit in the house, to power a secondary consumer unit in the garage. The overall length of cable estimate is less than 50m.

The calculations I used were based on the run of cable with the 13kw load being the consumer unit in the garage. However, as I write this I've just realised the flaw in that method. Although, I have over-estimated the length of cable, not sure if that over-estimation is sufficient.

What calculator did you use?
13kW = 56.52A @ 230V
Breaker size = 60A
Volt drop over 50m for 10mm 70° SWA cable = 13.2V = 5.74%

The calculator I used is on the Cleveland Cable website.

Do you have to bury it, could you run if over the conservatory?

If you need two cables then I really think you need bigger trunking...

Yes it must be buried.

If I can get two cables, there will be two separate ducts for them as it's not advisable or allowed to run a Data cable next to a wired cable, they should be at least 200mm apart.
 
The calculator I used is on the Cleveland Cable website.
Doncaster cables also has one:

Putting in 50m and 13kW points to 16mm cable.

If you are contemplating a system with varying cable thickness due to duct issues you will have to do the volt drop calculations separately. 13kW = 56A is too much for 6mm buried even with 90C thermosetting rating :(
  • 6mm, 70C limit, table 4D4A reference method D, 46A max
  • 6mm, 90C limit, table 4E4A reference method D, 53A max
  • 10mm, 70C limit, table 4D4A reference method D, 60A max
Unless you can lower the demand your minimum is going to be 10mm as well as allowing for resin joints being put it to connect to 16mm outside of that section. Also remember if you do plan on running a thin section close to the 90C limit (say going for 50A max) the joints and thicker cables need also to have the same thermal rating.

If I can get two cables, there will be two separate ducts for them as it's not advisable or allowed to run a Data cable next to a wired cable, they should be at least 200mm apart.
If the mains is SWA then you can run data cables next to it no problem as they are electrically screened, but if the power cable is running at quite a high temperature (e.g. assumption of operating close to 90C limit) you might have to check the thermal suitability of the network cable.
 
The calculator I used is on the Cleveland Cable website.

What cable did you pick?
You can only wire 90°C cable to devices that are rated for 90°C.
 
Doncaster cables also has one:

Putting in 50m and 13kW points to 16mm cable.

If you are contemplating a system with varying cable thickness due to duct issues you will have to do the volt drop calculations separately. 13kW = 56A is too much for 6mm buried even with 90C thermosetting rating :(
  • 6mm, 70C limit, table 4D4A reference method D, 46A max
  • 6mm, 90C limit, table 4E4A reference method D, 53A max
  • 10mm, 70C limit, table 4D4A reference method D, 60A max
Unless you can lower the demand your minimum is going to be 10mm as well as allowing for resin joints being put it to connect to 16mm outside of that section. Also remember if you do plan on running a thin section close to the 90C limit (say going for 50A max) the joints and thicker cables need also to have the same thermal rating.


If the mains is SWA then you can run data cables next to it no problem as they are electrically screened, but if the power cable is running at quite a high temperature (e.g. assumption of operating close to 90C limit) you might have to check the thermal suitability of the network cable.


Sorry I should have clarified, the load won't be a definite 13kw, that's a figure I've chosen as the upper limit based on various circuits running simultaneously and accounting for rating the motor to 4x the stated kw. Also the distance/length of the cable is an over-estimation, in an effort to ensure the system would be over capable for the intended purpose.

Below are some of the figures I've used for my guestimation
Lighting circuit: LED batten 24w x 10 = 240w
Security Circuit: Maximum 1kw
Fridge Freezer: Maxmium 500 watts
Any given motor machine tool: 2kw (unlikely any will more than this) increase rating x4 8kw

All in less than 10kw would be in use simultaneously.

If my methodology is wrong, please do correct.

Running the two cables together may not be an issue, however I'd rather err on the side of caution. Ultimately, if I have to dig and the cost isn't massive, then doing 2 holes isn't a problem. The problem arises, trying to thread two sets of cable through the existing pipe, which based on the information I've received above ain't going to happen for the 10mm cable. Therefore, I'd have to drop down to 6mm cable and use smaller machines
 
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.
 
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.
 
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.
 
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.
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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.
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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.
 
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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.
 
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).
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So it is a major step up from the current T&E routed through!
 
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.
 

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