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5 Special Safety Precautions against Damage to Underground Electricity Cables
Large construction or demolition projects place particular demands on the working party with respect to protecting U/G cables. Similarly, special safety precautions apply when U/G cables are found to be damaged or at risk, when plant or other utilities are to be installed near U/G cables, or when there is any doubt about cable identification between the different utilities. The involvement of the electricity supplier is crucial in all of these circumstances.
5.1 Large construction works
5.2 U/G cable found damaged
5.3 Doubt about identification of cables amongst different utilities
5.4 U/G cable found in shallow cover
5.5 Installation of plant or other utilities close to U/G cables
5.1.1 In large construction projects, the safe system of work for working near electricity supply lines can be integrated into the site contractor’s Permit-to-Dig system. This helps working personnel to check that all reasonable steps have been completed prior to excavation and aids compliance with all reasonable measures, as specified in the Permit, in the course of the works.
5.1.2 The working party has a duty to give sufficient notice to the relevant electricity supplier so that adequate precautions can be taken to ensure the safety of U/G cables within and adjacent to the works site.
5.1.3 For large development construction or site demolition, the working party should:
(a) identify all U/G cables that need to be diverted. These U/G cables are treated as live unless they have been confirmed by the electricity supplier the otherwise, or unless the diversions have been completed by the electricity supplier;
(b) protect all in-service U/G cables by appropriate means, in particular those subjected to pressure by construction traffic; and
(c) designate a cable reserve to help control the separation distances from other underground utilities. A marked-up cable reserve plan should be posted on site by the builder/developer for the information of all those involved in excavation and ground works.
5.2.1 If an U/G cable is damaged, the electricity supplier shall be notified immediately, regardless of how slight the damage and even if it is only on the cable sheath. The working party shall keep people well clear of the area until the electricity supplier has attended the site and given further safety advice. Under no circumstances shall any unauthorized repairs be made to the U/G cable.
5.3 Doubt about identification of cables amongst different utilities
5.3.1 The typical colours, sizes and buried depth of CLP’s and HEC’s U/G cables are given in Table 2 of Appendix 3. The working party and the competent person should be aware that there is NO standard colour coding system identifying all U/G utilities services. Certain high voltage U/G cables may look like water pipes; some U/G cables are yellow and mistakable for polyethylene gas pipes. The electricity supplier should be consulted if there is any doubt about the identification of cables amongst different utilities.
5.3.2 Unless the underground service is proved to be of another utility, this service shall be treated as a LIVE cable whenever works are carried out in its vicinity.
5.4 U/G cable found in shallow cover
5.4.1 If an U/G cable is found to be in shallow depth, the working party shall ensure that the electricity supplier is notified before the excavation is backfilled. The electricity supplier shall take remedial action to safeguard electricity safety as far as reasonably practicable. Where the cable plan is proved inaccurate, the electricity supplier shall amend its records accordingly.
5.5 Installation of plant or other utilities close to U/G cables
5.5.1 Installation of plant or other utilities should be kept away from the U/G cable as far as practicable. It is essential that the electricity supplier should be consulted prior to the construction of any manhole, chamber or other structure over, around or under an U/G cable.
5.5.2 As far as practicable, new utilities installations should be separated from existing U/G cables by the distances agreed with the electricity supplier. In general, the minimum clearance shall be 300mm for U/G cables of below 132kV and 1m for 132kV and above to allow for future maintenance or emergency operations.
5.5.3 Any working party which carries out works near U/G cables shall observe any reasonable requirements made by the electricity supplier for protection of U/G cables. Where there is any doubt about the reasonableness or adequacy of the electricity supplier’s requirements, or where the measures called for are not adequately implemented, the Director, upon request, shall decide whether the electricity supplier’s requirements are reasonable and/or whether enforcement action is required according to the ESLPR.