4.6 Protection of cables
4.6.1 Identification of underground cables
4.6.2 Protection general
4.6.3 Protection – mechanical
4.6.4 Protection – above ground
4.6.5 Protective earthing of cables
4.6.6 Records
4.6.1 Identification of underground cables
The presence of buried underground electric cables and underground control cables should be identified. Accepted methods of identification include:
Where the depth of cover is between 600mm and 900mm:
- laying a strip of bright orange polyvinyl chloride or polyethylene or similar marker tape above the cable. The tape is to have the words electric cable or similar, boldly printed on the upper side continuously along its length, and
- where appropriate, using on-ground or above ground marker systems.
The position of marker tape, should provide effective warning to anyone engaged in manual or machine excavation.
Where the depth of cover is 900mm or greater, it is not a requirement to place cable protection covers or marker tape above the cable or conduits. However, the location of cables should be marked with permanent on-ground or above ground cable marker systems.
4.6.2 Protection general
An electricity entity should have procedures in place to protect people and prevent damage to underground cables during excavation near underground cables.
These procedures should include but are not limited to:
- maintenance of ‘as installed’ records of underground cables by an electricity entity;
- provision at the worksite of ‘as installed’ underground cable records to anyone concerned with planning, organising and supervising excavation work;
- the use of records and other locating methods to positively identify the position of underground cables; and
- exercising care during subsequent excavation.
4.6.3 Protection – mechanical
In addition to the principles outlined in the section, Identification of underground cables and protection general, mechanical protection should be provided to minimise the risk of injury to anyone digging by hand near underground cables by:
- providing the minimum requirement for mechanical protection of underground cables in accordance with the table opposite.
|
Cable Location |
Minimum Requirement |
|---|---|
|
Where the underground electric cables and underground control cables are installed with a depth of cover between 600mm and 900mm. |
Install the cable in a suitable conduit for application under roads, and LD Class electrical conduit for application in the electricity footpath allocation. For application outside the electricity footpath allocation LD Class electrical conduit with a polymeric cable protection cover complying with AS 4702 Polymeric cable protection covers (non-Queensland Government link) not less than 75mm above the cable or, polyethylene orange coloured pressure pipe of minimum rating PN10 for PE80 Class pipe complying with AS/NZS 4130 - Polyethylene (PE) pipes for pressure applications (non-Queensland Government link) OR A polymeric cable protection cover complying with AS4702, not less than 75mm above the cable. OR Approved bricks manufactured especially for the protection of electric cables. Assess the risk for each location type to determine the method of mechanical protection. |
|
Where the depth of cover for any underground electric cables and underground control cables is 900mm or greater. |
No additional mechanical protection is required. |
Note: Polymeric cable protection cover and approved bricks provide superior protection. These should be considered for locations where cables would not normally be found eg parklands or unsealed walkway easements. Also consider using armoured or metallic sheathed cable buried according to cable depths in this section.
For cable circuits requiring high security or where the risk of excavation is high, increased protection should be provided by:
- using a combination of the above provisions for mechanical protection;
- the use of a heavier duty conduit; or
- encasing the cables in concrete.
Where there is a risk of cable or duct damage by excavating plant or vibration, increased protection should be provided by:
- laying the cable at a greater depth; or
- selecting a less exposed cable route.
4.6.4 Protection – above ground
Looping, linking and servicing connections made above ground should be housed in pillars or pits that must:
- be externally marked to include the words electric, electrical, or electricity;
- be secured using a special tool or key;
- when enclosing switchgear, be constructed to prevent water from accumulating, unless the switchgear is specifically designed for operation when submerged;
- be designed so that an object (defined as a standard test finger AS/NZS 3100 Approval and test specifications-General requirements for electrical equipment (non-Queensland Government link)) cannot be inserted into the interior and come into contact with or within arcing distance of live parts; and
- Be installed in places where vehicles are not likely to damage them.
Where an underground electric cable or underground control cable is located between the laying depth prescribed in this section and a distance of 2.4m above ground, the cable must be suitably protected so that the cable will withstand, without undue damage, any impact that might normally be expected at that location.
4.6.5 Protective earthing of cables
When earthing single core cables, consider the special bonding arrangements used to minimise sheath losses and induced sheath voltages.
4.6.6 Records
Records should be current for all cable installations using maps, plans or computer databases. When preparing a record system, consider the following details:
- alignments;
- cable depths;
- number of cables;
- cable details;
- specialised backfill;
- reduced levels;
- direct buried or ducted;
- service history;
- position of joints; and
- date of installation.
Last updated June 2, 2009
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