4 Tips for using underground ducting

If you plan to make an underground running of any type of service, it should be run inside a duct. This will help to prevent damage to the service, and also alert others to its presence if they dig into the ground. The following four tips will help you to install your pipe or cable safely, and provide a base for the addition of any future services with minimal problems.

1. Choose the right colour

The colour of the underground ducting you choose is vital, as this will alert others to the type of service the duct contains. The most common colour classifications, designated by local authorities, are as follows:

Black: domestic electricity
Red: high voltage electricity (over 500V)
Yellow: gas piping
Blue: water piping
Grey: telecoms cable
Green: cable TV/fibre-optics
Orange: railway signalling
Purple: motorway lighting

2. Choose the right material

When your run is quite long, the best option is to use flexible ducting, which has a corrugated external wall to provide extra strength and a smooth inner wall. For shorter runs, single-wall PVC rigid ducting is usually used. Twinwall ducting is applied to areas that require extra strength, such as beneath heavy concrete on paths or roads. Getting the right material for your job is important.

3. Install your duct efficiently

Try to use as few bends as possible when your duct must follow an obvious route. A trench depth of around 30-45cm is best, unless installing water pipes, which require 75-135cm to avoid the risk of frost damage. Ensure there are no sharp stones in the bed of the trench - laying 5cm of sharp sand in the bed is helpful.

4. Use draw cords to draw pipes/cables through ducting

Draw cords help to pull cables or pipes through a duct easily. They tie on to the end of your pipe/cable after you push them through the ducting, then you simply pull the cord back through to run your service through the ducting with no fuss.

Some ducting comes with flexible duct coils that include the draw cord. If yours doesn't, then you should purchase it separately. A good trick for getting it through the duct is to attach a rag to the cord that is large enough to fill the duct, but small enough to slide through it. Attach a vacuum cleaner to the other end of the duct, creating an airproof seal with duct tape. Then, run the vacuum cleaner for a few minutes before introducing the rag tied to the cord at the opposite end, and the vacuum cleaner should quickly pull it through.