The installation of low voltage electric power cables


The cables should be run in continuous lengths between the termination points. Joints should only be used where specified or upon approval.

1. Installation Directly Underground – Below Ground.

Direct-buried cables must be buried at 650 mm depth and blinded with a minimum radial thickness of 100 mm of sand. Continuously along the cable route, a layer of concrete tile is layered over the sand. After backfilling and consolidating the trench, it will be sealed off. Cable markers shall be placed at regular intervals up to 75m in straight runs and where descriptions change. Marker tapes shall be laid wherever indicated. During installation, cables shall not be bent smaller than 12 x diameter.

In the ground, cables that follow the same course and are laid horizontally should be spaced no closer than 150 mm apart, with the exception of single-core cables, which should be laid in a trefoil formation and touching along their entire length. Separate cable markers should be used for each group of cables.

It is mandatory to install adequate cable markers of approved design at intervals of not more than 75 meters and at points where the route of buried cables changes direction. If markers are freestanding posts, they must be at least 150 mm wide by 75 mm high and exposed above ground.

The cable ends at access points shall be marked with labels indicating the cable size and circuits.

2. PVC Pipe For Burring Cables Underground

At the depth specified in the drawing, the cables should be installed in PVC pipes.  60 cm below the top of the finished floor is the minimum depth. A suitable size manhole with heavy-duty covers shall be provided when installing and maintaining cables.

PVC conduits enclosed in concrete shall be used to run cables under road crossings. The minimum conduit diameter is 150 mm, bends should be suitable for the cable, and conduits should extend 1 m on either side of the road.

Unless otherwise specified, cables under the floor or through walls should be run in conduits made either of PVC conduits or vitrified clay with a plastic sleeve to form a push-fit joint with glazed interiors on PVC. The conduits should have a minimum diameter in accordance with IEE regulations and have bent to fit the cables.

To prevent water, other foreign matter, and vermin from entering cable conduits and ducts that terminate in buildings, a waterproof sealing compound, and hardwood bushes must be used.  The spares should also be sealed in a similar manner.

3. Low Voltage Power Cables – Above Ground Installation

1. If cables change direction, the radius of the bend should not be less than the minimum required by the IEE regulations. Cable trays, ladder trays, or PVC pipes may be used unless otherwise specified.

2. In order to prevent cables from falling into a duct, air ducts should be fixed with aluminum alloy or approved non-flammable claw cleats and galvanized screws with BS 1490 bolts with the maximum spacing given in Table B2M. A single bolt should be used to secure cleats for cables up to and including 50 mm diameter and the stud should not extend beyond the tightened nut appreciably. To prevent deformation of plastic sheathing, excessive pressure must be avoided when using cleats on PVC insulated cables. Cables crossing open spaces should be supported by suitable supporting steelwork or a galvanized cable tray. This steelwork must be painted to prevent rusting. To know more information about the power supply cables you can read more here.