However, there may be a number of circumstances which cause depths to vary. In exceptional circumstances BT will assist with the location of its apparatus on site. Cable television services are laid to the curtilage of every premise in the franchise area, whether or not a supply enters the premises. These terminate at a small junction box placed as close as possible to the boundary of the premises. Services are normally laid from a supply cable situated in the nearest footpath which is normally at 250mm cover.
Cables are either small bore co-axial or optical fibre and are coloured black.
Cables are always laid in ducts which are coloured green and range in size from 25mm to 110mm diameter. Ducts laid in the carriageway are normally placed at a depth of 450mm cover and those laid in the footway are normally at a depth of 250mm cover. Where marker tape is used it is usually coloured green or yellow. Up to that time Mercury used white ducting to carry underground apparatus and the three CATV companies used green ducting. B.4.2 All white Mercury ducts contain fibre optic cables which include tracer wires to aid location by cable locators.