7.13.3 - Underground wiring

Three types of cable may be installed underground:

1. - armoured or metal sheathed or both

2. - p.v.c. insulated concentric type. Such a cable will have the neutral (and possibly the protective conductor) surrounding the phase conductor. An example is shown in {Fig 4.1(c)}.

3. - Any suitable cable enclosed in conduit or duct which gives at least the same degree of mechanical protection as an armoured cable.

No specific requirements for depth of burial are given in the Regulations, except that the depth should be sufficient to prevent any disturbance of the ground reasonably likely to occur during normal use of the premises. Hence, a cable to outbuildings installed under a concrete path could be at 400 mm, whilst if running through a cultivated space which could be subject to double digging would be less likely to disturbance if buried at 700 mm. For caravan pitches, cables should be installed outside the area of the pitch, unless suitably protected, to avoid damage by tent pegs or ground anchors.

Cables must be identified by suitable tape or markers above the cable, so that anyone digging will become aware of the presence of the cable. Cable covers may also offer both identification and protection as shown in {Fig 7.22}.

It is often useful to lay a yellow cable marker tape just below ground level so that this will be exposed by digging before the cable is reached. Careful drawings should also be made to indicate the exact location of buried cables; such drawings will form part of the installation manual (see {8.2.1}).

Fig 7.22 - Cable covers