Sch 4Requirements for earthing and electrical protection systems

Schedule 4—Requirements for earthing and electrical protection systems (regulation 52) ENA means Energy Networks Association Limited; listed standards means the standards (both national and international), codes, guides and other documents, as published from time to time, listed in the Appendix at the end of this Schedule; neutral conductor means a conductor or a group of conductors of a multi‑wired system of supply which is maintained at an intermediate and approximate uniform electrical potential in respect of the other conductors of the same circuit, or the conductor of a two‑wire system that is earthed at its origin; protective devices or equipment means devices or equipment intended to isolate the active conductors of a circuit in the event of an electrical fault. 2—Design—general (1) Earthing and protection systems must be designed to ensure— (a) reliable passage of fault and Single Wire Earth Return (SWER) load currents to earth; and (b) reliable and speedy operation of circuit protection devices; and (c) step, touch and transfer potentials with respect to assets associated with the circuit are safe; and (d) detection and isolation of electrical conditions likely to significantly increase risk to people or cause significant damage to property, and so as to comply with the listed standards or achieve, to the satisfaction of the Technical Regulator, the same or better safety and technical outcomes. (2) In determining abnormal electrical service conditions, due care must be given to the consideration of extremes that may occur, the likelihood of their occurrence and the associated risks. 3—Protection equipment All protection equipment must, to ensure safe operational performance, conform to the listed standards or achieve, to the satisfaction of the Technical Regulator, the same or better outcomes. 4—Earthing equipment and ancillaries Earthing systems must be designed to be constructed of material that is— (a) copper, copper alloy, stainless steel or some other material having superior corrosion resistance; and (b) electrically conductive. 5—Earthing of low voltage electrical supply networks (1) The earthing of low voltage electrical networks of supply must be designed to be a MEN system, unless otherwise approved by the Technical Regulator. (2) A MEN system must be designed so that— (a) a continuous neutral conductor connects all customers' premises in accordance with AS/NZS 3000; and (b) the neutral conductor is connected to earth at each distribution substation or generator. (3) A direct earthing system must be approved by the Technical Regulator and must be designed so that— (a) a continuous earthed conductor connects— (i) all customers' premises in accordance with AS/NZS 3000; and (ii) the neutral conductor at the distribution substation or generator; and (iii) every surge diverter, to earth at the generating station or distribution substation only; and (b) the earthed conductor is formed from— (i) the metallic sheath of an insulated cable providing the LV supply to the customers' premises; or (ii) a separate conductor of an insulated cable providing the LV supply to the customers' premises; or (iii) a separate earthing conductor affixed to structures supporting the LV supply circuit to the customers' premises; and (c) the system is earthed at the substations or generating stations. 6—Earthing of substations Substations must be designed to have an earthing system that complies with the listed standards or achieves, to the satisfaction of the Technical Regulator, the same or better outcomes. 7—Protection systems for low voltage aerial lines and underground lines Each of the aerial and underground service lines of a transmission or distribution network must form part of a circuit that is protected by protective equipment that can isolate each of the active conductors of the lines. 8—Step and touch potentials and earth potential rise Uninsulated metal or reinforced concrete that— (a) forms part of a circuit in a transmission or distribution network (excluding the current carrying conductors); and (b) is accessible to persons; and (c) may, in the event of a primary insulation failure of the circuit, experience a rise in voltage, must be effectively earthed to comply with the requirements of the ENA Guidelines for Design and Maintenance of Overhead Distribution and Transmission Lines  C(b)1, as published from time to time. 9—Installation of earthing and protection systems—general Earthing and protection systems must be installed in accordance with design requirements set out in this Schedule and to conform with the listed standards or achieve, to the satisfaction of the Technical Regulator, the same or better outcomes. 10—Connections and joints of earthing systems Terminations to earthing conductors and joints in earthing conductors must be of a type that utilises materials and techniques specifically developed for earthing electrical installations so as to comply with the listed standards or achieve, to the satisfaction of the Technical Regulator, the same or better outcomes. 11—Mechanical strength and protection of earthing systems Earthing conductors and other components of an earthing system must be installed in a manner that provides protection against likely mechanical damage, inadvertent interference and chemical deterioration. 12—Maintenance—general (1) Protection and earthing systems must be maintained to be in a safe operating condition. (2) A system of maintenance must be instituted for protection and earthing systems and their components, including— (a) predetermined processes to confirm the safe state of components; and 13—Inspection and testing of earthing systems (1) Earthing systems must be inspected and tested from time to time to ensure that the design requirements of— (a) resistance to the general mass of earth; and (b) electrical capacity; and (c) step, touch and transfer potentials; and (d) corrosion resistance, are being maintained. (2) The condition of earthing systems must be verified by instruments designed for that purpose. 14—Inspection and test results of earthing systems The results of visual inspections and resistance readings must be recorded and audited to identify changes that would influence the frequency of inspections, tests and maintenance. 15—Inspection and testing of protection systems (1) Protection systems must be inspected and tested from time to time as required according to the risk of damage to, or aging of, components or changes in the network electrical parameters, to ensure that— (a) detection sensitivity; and (b) speed of operation; and (c) discrimination of load currents; and (d) co‑ordination with other protection systems, of the systems are being maintained. (2) The performance of protection systems must be verified by instruments designed for that purpose. 16—Inspection and test results of protection systems The results of visual inspections and performance tests must be recorded and audited to identify changes that would influence the frequency of inspections, tests, maintenance and replacements.