Top tips for using underground ducting


Needless to say, if you’re running any type of service underground – be it gas, electricity or water, for example – then it should be run inside a duct.

Underground ducting protects the pipe from damage and also alerts groundworkers to its presence. There are several options to choose from which can make it tricky, however, our team is here to offer a few useful tips for ducting pipes – ensuring maximum safety and minimal fuss.

  • Pick the right material – do you need flexible cable ducting that has a smooth inner wall and corrugated exterior for additional strength? Or is a PVC duct sufficient? Flexible ducts are most suitable for longer runs whilst PVC is typically used for shorter runs. Twinwall ducts are also an option, and ideal for heavy traffic areas, i.e. under pathways and roads.
  • Identify which colour ducting you need – getting the colour right is crucial when it comes to underground cable ducting. You can’t just pick any! The colour of a ducting pipe is determined by the classifications used by the local authority; with black being used primarily for domestic electricity, blue being for water, yellow for gas, grey for BT and telecommunications, green for cable TV/fibre optics, orange for railways and traffic signals, purple for motorway infrastructure or street lighting in Scotland, and red symbolising danger (high voltage electric).
  • Take care with the installation – as a general rule of thumb, try to avoid using too many bends and, if possible, allow your duct to follow an obvious route like alongside a patio or pavement. The depth of the trench will vary depending on the service being carried, and make sure there are no sharp stones on the bed of the trench. You may also consider using marker tape to indicate the presence of electric cables.
  • Drawing pipes and cables through the duct – this largely depends on the type of underground cable ducting. Flexible duct coils are supplied with a draw cord pre-installed which makes it easy to pull cables or pipes through. It’s also worth adding a second cord to the pipe before you draw it through the duct in case you need to introduce additional pipes later on. Meanwhile, BT ducts don’t come with a cord but you can purchase one separately and use a rag and vacuum cleaner.
  • Join the lengths of duct – as standard, a flexible duct will come with a joiner attached at one end and additional couplers are available. Twinwall ducts are plain ended and joined using couplers too. Typically, black PVC ducting and grey BT ducting both have a blown socket at one end which allows you to join two lengths by placing the plain end of one pipe into the socketed end of another. You will then need to take a small piece of wood and put it at the other end of the length before tapping gently with a hammer or mallet.

For further information about using underground ducting, you’re more than welcome to contact our experts, here at Cotterill Civils.

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