CUSTOMER CABLING:
HOW TO ASSESS THE RISK OF INJURY? Terry Phillips, former member of the various Wiring Rules committees 1991-2013
In the last issue of ECD Solutions, we explained the requirements for customer cabling between separate buildings and why the use of metallic telecommunications cabling between buildings may be risky. This issue, we explain how a cabling provider can assess that risk.
A
ssessment of the risk of injury to the end user of a telecommunications service, as required by Clause 10.1 of AS/CA S009, is carried out in accordance with Australian Standard AS 4262.1, Telecommunications overvoltages Part 1: Protection of persons. Factors affecting the probability of a lightning-generated overvoltage occurring are listed in AS 4262.1 as follows: (a) known lightning damage or injury history within the vicinity of the premises (eg, if Telstra has routinely installed lightning protection on the lead-in cable or is known to routinely install it in the area); (b) number of thunder days per year for the geographical area (a thunder day is a day on which thunder is heard at least once); (c) building density - the number of buildings within 100 m of the location under consideration (this provides a measure of the number of connections to earth of the local electricity distribution system); (d) soil resistivity - the higher the soil resistivity, the greater the area of influence of a lightning strike to ground and the higher the risk;
8 ECD SOLUTIONS - SEPTEMBER/OCTOBER 2014
( e) exposed terrain - elevated locations over 1000 m above sea level or prominences in the terrain, such as cliff tops, ridges, bluffs and hills, are considered to be at greater risk; ( f) building construction - concrete slab and metal-frame construction create a greater earthed environment, increasing the risk that a person may be in direct or indirect contact with local earth during a thunderstorm; ( g) aerial telecommunication cable construction - the risk is considered to be higher if the premises is fed by more than 200 m of aerial cable within approximately 2 km of the premises; ( h) isolated telecommunication service - a service located in a building or structure that is not connected to any public electricity supply system (or where the public electricity supply earth is more than 100 m from the building or structure at which the service is used) is considered to be at higher risk. How the above factors are applied to determine the level of risk for a particular location is conveyed in AS 4262.1 in the form of a flow chart.
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