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BUILDING SERVICES
Ref: BCA 17-07 Current at: September 2017
ELECTRICAL EARTHING REQUIREMENTS This information sheet has been developed to provide information to HIA members on the electrical earthing requirements in Australian standard - AS/NZS 3000:2007 - Wiring Rules. What is electrical earthing? Earthing is used to protect people from an electric shock. It does this by providing a path (a protective conductor) for a fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault. Earthing therefore provides a safety factor for people and is essential and mandatory. For house installations commonly you will see a metal bar/rod sticking out of the ground with a green and yellow (or similar coloured) earth wire tied to the bar/rod. This forms part of the earthing installation. Electrical wiring rules In Australia electrical installations are regulated by state and territory legislation and that legislation calls up the joint Australian and New Zealand Standard AS/NZS 3000 – Wiring Rules. AS/NZS 3000 sets out the requirements for the design, construction and verification of electrical installations, including the selection and installation of electrical equipment forming part of such electrical installations. Clause 1.4.44 of the standard defines what are deemed to be an ‘earthed situation’ and Section 5 of the standard contains the detailed requirements for earthing i.e. when it is required and installation requirements. For electrical installations for houses HIA’s building services team receive calls in particular, regarding what are the earthing requirements for the following:
Steel framing, including for structural beams and lintels Reinforced concrete slabs in showers and bathrooms Swimming pools and spas, including pool fences.
Below is a description of the relevant requirements. Steel framing, including for structural beams and lintels Clause 5.4.6.2 of AS/NZS 3000 requires that steel framing forming the frame of a house be earthed. However, it is not necessary to earth individual lintels, posts, metal window frames or steel trusses mounted on timber walls. Insulated shrouding though may be required where terminations to electrical equipment cannot maintain double insulation, when they are in close proximity to conductive building materials. The requirement for earthing of steel framed structures is not required to structures, such as a carport or shed, that do not have electricity connected to them.
Reinforced concrete slabs in showers and bathrooms Clause 5.6.2.5 sets out the requirements for showers and bathrooms to minimise the risk associated with any voltage differences that may occur between electrical equipment connected to the electrical installation earthing system and any conductive piping (including taps etc.). The requirement states: “Any conductive reinforcing within a concrete floor or wall forming part of a shower or bathroom shall be bonded to the earthing system of the electrical installation to avoid any potential differences that may occur between the conductive piping (including taps, drain, etc.) connected to, or in contact with, the electrical installation earthing system and the concrete floor or wall. An equipotential bonding (defined in AS/NZS 3000) conductor, in accordance with Clause 5.6.3, shall be connected between the reinforcing material and any part of the earthing system within the room.” The notes to the clause indicate that reinforcing mesh or tie-wires laid in the floor and connected to the equipotential conductor may be used. This requirement does not apply to existing concrete floors or walls, although the practice is encouraged wherever practicable. It is suggested that the builder coordinate between the trades to ensure the proper placement of the earthing system for the showers and bathrooms. Swimming pools and spas Clause 5.6.2.6 sets out the earthing requirements for swimming pools and spas. The requirement states: “For swimming and spa pools the following items shall be equipotentially bonded: (a) The exposed conductive part of any electrical equipment in the classified pool zones. (b) Any exposed conductive parts of electrical equipment that are not separated from live parts by double insulation and that are in contact with the pool water, including water in the circulation or filtering system. Where any of the items described in (a) or (b) exist, the bonding shall be extended to the following additional items: (i) (ii) (iii)
Any fixed extraneous conductive parts of the pool structure, including the reinforcing metal of the pool shell and deck. Any conductive fittings within or attached to the pool structure, such as pool ladders and diving boards. Any fixed conductive metal within arm’s reach of the pool edge such as conductive fences, lamp standards and pipework.”
The clause also prescribes that where the bonding conductor connection may be subjected to detoriating effect of the pool water that it be covered or encased in a suitable compound. Additionally, it states that the bonding conductor shall be connected between the bonded parts and the earthing conductor associated with each circuit supplying the pool or spa, or that earthing bar at the switchboard at which the circuit originates. Clause 6.3.3.2 also contains some suplpementary earthing requirements for protection against electrical shock. Pool fences A question commonly asked is whether a conductive metal pool fence requires earthing/bonding? The common view on this issue is that earthing/bonding is not required unless the conductive parts of the fence are within arm’s reach of the pool edge. It is important to note that the process of connecting an earth wire to the conductive material is deemed ‘electrical work’ and must only be carried out by a licensed electrical work. Additionally, the information provided herein is of a general nature and it is recommended that you consult a licensed electrician or the relevant electrical authority in your state for the project.
HIA members can contact HIA’s Building Services staff for more information on 1300 650 620 or
[email protected]
