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Everything you need to know about Underground Ducting

If you’re planning to do, or in the throes of carrying out some DIY on your home, underground ducting is an area you should read up on just in case you need to replace some pipes around your home. Of course, for any major works you should of course always seek the help and advise from a reputable builder –

Here’s a very brief overview on the different types of underground ducting and the colour codes explained.

When to useshutterstock_1285620898

If you’re planning on running any kind of services in the ground, it must be run inside plastic underground ducting. There are two main reasons as to why this is important, firstly it protects the service from damage and secondly it alerts its presence to anyone else who may be carrying out excavation works in the future. Choosing the right kind of duct is as important, as this also protects your service. For instance, if you have a short run, single-wall PVC rigid ducting is normally used. For longer runs the best material to use is flexible ducting. Flexible ducting has a corrugated external wall which makes the ducting stronger and a smooth inner wall. You can also buy twinwall ducting which you can use for runs which require additional strength such as under concrete or patios.

Which colour to use

All underground ducting should be colour coded to comply with safety and building regulations. The colour coding also alerts others to the type of service housed within the ducting. It’s important to understand and adhere to the UK’s universal ducting cable colour codes. Here is a table to help explain:

Colour Use
Black Domestic mains electric cable, low voltage
 Red High voltage electric cable
Yellow Service and mains gas cable (ducting is perforated to allow for gas venting)
Blue Water pipes installed at least 750mm below surface
Green Broadband, telephone and non-motorway CCTV cables
Grey BT or telecommunications cables
Purple Motorway service cables for speed cameras, traffic cameras, emergency phones etc
Orange Street lighting and traffic signalling cables (i.e. traffic lights)


How to install

It’s always best to install your ducting with as few bends as possible and for it to follow an obvious route. Most trenches should be dug to about 300mm to 450mm, but for water pipes it should be 750mm to 1350mm to avoid any potential risk from frost. You can also use marker tape to indicate the presence of electric cables. Make sure there are no sharp stones and use a 5mm bed of sand will help protect your ducting. For more information and advice visit the Health and Safety Executive website:

How to draw pipes and cables through the duct

To make it easier, flexible duct is supplied with a draw cord. It’s advisable to use a second draw cord and then leave it in place once you have pulled your pipe or cable through as this can then be used if you need to add an additional cable. For other types of ducting that do not have a draw cord a top trick is to attach a small rag to the end of your cable so that it can be pulled through without getting stuck. Attach a vacuum cleaner to the other end of the duct and make it airtight by sealing it with duct tape and then turn the hoover on. Do not try and suck the pipe through to begin with, let the hoover dry the duct and then after a few minutes introduce the cable which should then be pulled through the duct.

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