BASEC News

Phased Installation of Cables

03/08/09
Most if not all cable installations are carried out in a number of phases - it is less common for cables to be installed and fully terminated at once. It is important for the installer to check cables at each stage to maintain their future performance.

Final circuit installation cables are often run into a building at first fix, and they can then sit for a number of weeks or months before final fix, inspection, testing and finally energising.  If a problem is found later, there will be cost and delay in their replacement.  Installer should perform basic checks on cables at this stage, and secure them until final fix.  Check that the cable meets the required specification.  Simple visual inspections, continuity checks and insulation resistance checks will quickly identify most common cable problems.  Finally, the un-terminated ends should be protected by coiling and covering with tape.

Armoured cables used for power distribution are commonly installed below ground between or within buildings, or from transformers and switchgear rooms.  Their construction leaves air gaps between conductor strands, between individual cores, and between armour wires.  If water penetrates these spaces problems could be experienced with insulation resistance readings.  Over the long term there could also be corrosion of conductors or armour wire, which could affect safety.  For this reason the British Standards for these cables require both ends to be capped.  Caps are fitted in the factory, and should always be refitted when lengths are cut by the cable distributor for delivery to site.  However, sometimes these are left off - and insulation tape is no substitute for a proper cap.  Caps should be replaced by the installer before leaving the cable for any length of time.  It is also useful to check continuity and insulation resistance at each stage of the installation to make sure that no damage or degradation has occurred in the interim.  Doing this will help avoid unpleasant surprises.

Further information and assistance is available at www.basec.org.uk, technical@basec.org.uk, or contact BASEC directly on 01908 267300.

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