Hi all, I’m new to the forums, but basically, I have just purchased a new house and the previous owner decided to run some 6mm Twin Earth to the garage, underground in some PVC pipe over a distance of about 20 meters, and only buried about 15cm underground! As I am getting the drive re-done I am looking to re-do the job with some 10mm SWA and 32mm polyduct, buried to about 50cm under the new drive. Now the electrical wiring side of things is no bother what-so-ever. Nice easy job. However when it comes to the polyduct I have a few queries, so first little background on how the current Twin Earth is laid. When you come into the house through the front door there is a little vestibule where the CU is located. The wall at the side (to the outside world) has been drilled through, then the 6mm Twin Earth has been pulled through the hole, into PVC pipe going vertically down the wall (about 1 foot), underground from the front of the house to the side of the garage, up 1 foot of PVC pipe attached to the side of the garage, then through a hole at the bottom of the garage wall. So I would like to follow the same route (through the holes in the side of the garage and house that already exist). I was planning on running the SWA out of the hole in the garage wall, going down the side of the garage wall (clipped direct), into the polyduct which will be laid underground, running it all the way to the front of the house, then exiting the polyduct, going up the wall on the outside of the house (clipped direct), then into the existing hole in the wall and into the house. My questions are as follows...... 1. Do I need to create a proper seal at either end of the polyduct, with some kind of glanding, silicon or something? Basically, I am thinking about moisture getting in. 2. If I need to make a good seal where the SWA exits the polyduct, how do I do it? 3. Can I just leave the polyduct horizontal on the ground and have the cable come out of the polyduct, then make a shallow 90* bend in the cable to bring it vertically up the wall? 4. Would it be better to I make the shallow 90* bend in the polyduct itself so the cable exits the polyduct in an already vertical position? 5. If it is the latter of questions 3 & 4, do I need to seal and prevent dirt, etc getting into the polyduct as it gets burried, and if so, how? I appreciate this has been a long post, and I would greatly appreciate some advice on the above. I suspect I may be over-thinking it, but would rather do it right the first time. Wiring is no issue at all for me, but I have not had to deal with it being buried underground before. Thanks!
I just bury the swa in ground directly myself. Add a bit of sand around it and back fill. Can't remember how deep the regs say but I think it's about 2 foot so 50mm not really deep enough. Someone else will know. You also need "danger electric cable" tape just below the ground surface and above the buried swa to show the route.
Vestibule: Posh word for a porch! Quite clear to me how it's been done SWA should be 450mm minimum I seem to recall, might have been changed now, but 600mm seem to be the prefer nowadays. Just terminated swa into a IP56/IP65 Adaptable Box, then use t&e through the wall to cu.
Cheers guys, but I wrote 50cm (500mm). From what I have seen the regs say 450mm, but I doubt think the builder will complain much if I ask him to dig the trench an extra 100mm to make it 2 foot. Moving on…. @KIAB why do you say to terminate in an IP56/IP66 rated enclosure with appropriate gland then take T&E from there into the main CU? Would it not be better to just run the SWA all the way? @Columb I will try to get pics up for you, but all I mean is you that when you look at where the CU is, the wall next to it has been drilled through, and then they have pulled the Twin Earth to the outside from that hole and stuck it into PVC pipe going vertically down the wall (about 1 foot) until it goes underground and onto the garage. Also, the reason I am wanting to go for polyduct is from what I have read, this adds extra protection and negates the need for the warning tape at 150mm deep. However it is more for the extra protection it offers. It's what the suppliers use under roads (at deeper depths), so if it's good enough for them, I would rather use it also for that extra piece of mind. So any thoughts on how the polyduct should be done & if it needs to be sealed to prevent moisture entering, etc?
You can terminate the swa in a separate box then run twin and earth from the box to the c.u. or terminate straight into the c.u. If you use t + e it will need to be surface mounted all the way into the c.u. or if at a depth of less than 50mm you will end up needing an rcd at the start of the run which is not a good design for a sub main. Really not sure why you want to use polyduct, I've seen loads of swa directly buried without a problem providing your not running it through marshland or something like that I can't see how polyduct is going to help at all with moisture or added protection but if you want to do it like that then knock yourself out. Also you still need warning tape what ever you put it in.
Polyduct offer little if any extra protection, better to bury swa deeper. You will struggle to get 10mm swa to bend tight enough to get it through wall,most likely impossible, I always find it easier to terminate in adaptable box, one house end, one garage end, then run T&E from them into house/garage to cu's. Just bed & cover swa with sand before back filling with soil.
ben I wonder if you have seen street services run in different colour polyduct? I can only think it's done like that for identifcation. Anyway street level services are not covered by bs7671 anyway so they pretty much do what they want out in the badlands.
It is. Polyduct is industry standard colour coding. Black (B) - Electricity Yellow (Y) - Gas Orange (O) Street Lighting Blue (BL) -Water Purple (P) Motorway Communications Green (G) Cable Television Purple (P) Street Lighting (Scotland) Grey (GR) - Telecommunications -
Hmm, so you guys think there is absolutely no need to use polyduct (or similar) while still complying with 17th edition wiring regs? Good point about bending the 10mm SWA into the walls....might have to go for something like this... https://www.tlc-direct.co.uk/Products/WK1010B.html Will mount it to the outside walls of the garage / house while using the correct rated glands and finish off with as little 10mm Twin & Earth I can (so just inside and to make the bend through the walls).
Western Power Distributions criteria: A trench 530mm deep and 300mm wide, the trench should be level and free from any sharp stones or objects which could damage the service cable. The reinstated with 75mm stone dust, or ducting obtainable from the WPD office. **The above applies to mains supply cable only**
Just a question, I have a load of 63mm blue twinwall ducting left over from a job, If I used black PVC tape to cover over the pipe would this be allowable? Had to buy a 50m coil, and only used 3m!
I would use larger than 32mm. It's too small for your need really. 63mm would be ideal. I would prefer to see the duct brought up to the surface. Preventing water ingress is not going to happen. It will fill with moisture. There is little you can do to prevent it.
I was thinking the same thing lec. Although the size is refereed to as an internal measurement. The next size up it seems is 38mm internal bore in polyduct?
Ok, now we have 2 people saying polyduct is a waste of time and 2 others recommending I use it, but go for a larger size.....is there a definitive answer as to the correct method??
Personally I think its a good idea. About water getting in from the other end. You can simply lay ducting with a slight fall to stop water getting in, or just create dip near to the end.
I wouldn't be over fussed with ducting it, there is no requirement to, but it's a good job done if you do. If you buy a coil and have more than you need, run two, and you have one for data/phones if required. How about a water pipe?
Thanks, I might not bother then as polyduct isn't cheap stuff and the money could be better put into other parts of the house. Also,I was thinking, instead of using a junction box to join some T&E with the SWA I may be able to simply drill a new hole in the wall of the hous entering at 45* to give a gentle bend radius. The one for the garage is already done that way and might mean I can just go direct from the CU in the house to the CU in the garage with no external joins.
If your really intent on running swa in pipe, why not use 40mm solvent weld waste pipe -£4.40 for 3m from our hosts. Join with couplers and obviously solvent weld cement I guess not really designed to be buried but can't see it "dissolving" In a year or twos time
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