Overhead power lines insulation failure

The Queensland Electrical Safety Office has been made aware, by Energex, of defects in some existing overhead insulated service lines, according to a statement issued by the Queensland government. Routine safety inspections of service lines, which are normally the wires that connect homes and businesses to the electricity power pole, have identified that the insulation casing on some overhead service lines have deteriorated prematurely. The deterioration could result in live electricity conductors being exposed.

Energex has commenced a power line inspection and replacement program across Southeast Queensland, according to the statement. Distribution entities have been informed of the insulation failure, as it may not be restricted to the Energex network. The deterioration of insulation is most obvious on the upper side of the power line, which is directly exposed to sun. Therefore, a visual inspection, from the ground, may not identify this deterioration. While this failure is relevant to the electricity distribution network operator, the supply of this product could extend to the general electrical industry, such as a private installation. A particular application in this case would be where an electrical contractor has installed this type of aerial cable from one installation to another.

The Electrical Safety Office reminds workers and the general public to take extra care when in the vicinity of power lines. Always treat power lines as live and hazardous, the statement warns. Home owners or business operators who identify defects in the service wire to the premise should contact their distribution network provider. Where defects are identified in private aerial conductors the owner of the line should contact an electrical contractor.

Power lines are usually installed above ground, however, they may also be underground. Locating power lines can be difficult even on bright sunny days and more so in low light, rain, cloudy weather, or at dawn or dusk. To stay safe it is essential to be careful and observe safe practices whenever you are near overhead power lines or carry out activities that penetrate the ground such as excavating trenches or drilling holes. Next time you are working near power lines: treat them as live and hazardous; look at the site and identify all risks; if there is any risk of injury to yourself or others, use appropriate risk treatment measures and maintain exclusion zone distances.

Exclusion zones
An exclusion zone is the minimum safe approach distance from an overhead power line. Exclusion zones can vary according to: 

• The voltages and types of overhead power lines
• The work being carried out by people, plant or equipment near the power line
• Whether the operator is an authorised or instructed person in accordance with the Electrical Safety Regulation 2002.

High voltage electricity can jump gaps: You are not protected from an electrical incident just because you are not touching power lines. The size of the gap electricity can jump (the arcing distance) increases with the voltage - the higher the voltage, the bigger the arcing distance.