Underground Ducting – Colours Explained


Plastic Ducting has now become by far the most commonly used way of protecting pipes and cables that are laid underground, both in domestic houses and gardens and in commercial installations such as under roads or playing fields. Whilst clay ducts are still often used in certain larger commercial projects, it is equally likely that larger bore plastic pipes will be found in today’s construction sites. Providing ducting is laid correctly, it offers a number of benefits to an underground installation. Ducting primarily gives protection to the cable or pipe within from ground movement and animal activity, but it also alerts any future installation to the presence of a pipe or cable, often preventing costly damage and remedial works. It also makes it far easier to replace existing cables, or even add more, without the need for large excavation works.

Although water supply pipes have to be laid at depths governed by strict guidelines, other services vary greatly – there are actually few rules governing other services. Whilst it is usual for most services to be found at depth of at least 300mm, it is quite possible to find a duct laid just below ground level, particularly near to the external walls of a house. It is therefore equally likely that you may well discover such a duct whilst carrying out property maintenance or gardening, and therefore it would be helpful to understand which service cable or pipe is being carried within.

Black duct is generally used to carry electricity. The voltage of a cable laid in black duct should be low (less than 250V) or medium (less than 500V). Higher voltage cables (greater than 500V) are to be found in red ducts and should never be found near the surface.

Yellow duct contains gas pipe. This pipe would usually be made of polyethylene, and is used to supply the gas to incoming side of the gas meter.

Blue duct is made to carry potable (drinkable) water. In most instances this would be MDPE (medium density polyethylene) water mains pipe.

Grey duct is used by telecoms providers to carry their cables. A more recent addition to the colour spectrum is green, which is the standard used by cable television companies. During the cable television boom of the 1990’s many miles of green ducting were laid in the UK’s towns and cities.

Orange duct is reserved for commercial use, and carries cabling for traffic signals. This is used in both highway and railway applications, but is most commonly used by railway maintenance contractors. This should not be mistaken for standard foul and surface water underground drainage pipe, which is a golden brown colour. The ducting that is used for traffic signals is a much brighter orange colour.

The other colour of duct that is now commonly visible is purple, usually seen when motorway maintenance is being carried out. Purple duct is used to carry cable for lighting and overhead gantries.

Ducting is generally available from Builders Merchants and Civil Engineering suppliers. Most types of duct come in standard lengths of 6 metres, with a male and female end for easy push -fit jointing. Smaller sizes of duct for domestic use are also supplied in coils, of usually 50m in length