Sealing underground ducting

[ColinJones]

What are the rules/best practice regarding sealing underground electrical ducting? Lets say you have SWA in a 50mm duct from a house to an outbuilding. What happens if you can't bring the duct up inside the building at one end? If you leave the end of the duct underground it's likely the duct will fill with water. I know SWA can be installed in the ground without a duct at all but how does that compare with a duct partly full of water?

 

[Engineer54]

There are propriety duct sealing compounds on the market for use in contact with soil. There shouldn't be any problem with SWA cables sitting in water, unless of course there is any sheath damage to the cable. Then you could be in some serious trouble if your using the SWA as your CPC.

 

[johnboy6083]

expanding foam can also be used to seal ducts. its good practice with expanding foam, to tape the cables up, above the level of the duct. spray the foam, and when it expands, it wont stci to the cable, once it leaves the duct.You then cut the foam down, and remove the tape. jobs a good un

 

[oxocube]

There shouldn't be any problem with SWA cables sitting in water

It's a big problem they are not suitable for continuous immersion in water. The duct must be sealed at both ends to prevent water and vermin ingress.

 

[ColinJones]

Thanks. Will check out duct sealing compounds. Won't be relying on the armour as cpc. I believe I could but I already have some three core.

 

[Engineer54]

It's a big problem they are not suitable for continuous immersion in water. The duct must be sealed at both ends to prevent water and vermin ingress.

You had better tell that, to virtually every farmer in the UK!! Ask them if their cables have been any problem, over the years. Of course what your saying is correct all ducts should be sealed at both ends, internal and external. I would say that vermin are a far bigger threat to any armoured cable than cables sitting in water....

I've known cable duct systems carrying multiples of cables both LV and MV, some even with T joints in them in the large 3.5m x3.5m underground chambers, that flooded to over flowing every rainy season. Because of both the cable duct system construction and the positioning of the cable chamber room being located at the lowest point on the site...lol!! They will be like that forever more, as there is literary nothing they can realistically do about now... It's a long story!! lol!!


it was like that over 15 years ago when built, it was the same 10 years ago when i was on the project, and a friend that goes to this site on business 2 or 3 times a years says it's the same now!! As bad as this situation is, it has Never caused a single problem from being submerged in water for around 8 months of the year, every year.

For anyone in Saudi that wishes to see this mess, it's on the King Abdulaziz City for Science and Technology (KACST) site in Riyadh, on the cities housing side of the project ...