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Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.
Internal electrical power services
Internal electrical power services include meter boxes and distribution boards, and methods of surge and RCD protection and earthing.
On this page:
- Smoke alarms
- meter box
- distribution board
- surge protection
- residual current device (RCD) protection
- working on existing buildings.
Installing smoke alarms is mandatory as part of all new residential construction work. Alarms must be on or near the ceiling and have a test function to check that they work properly. Under Acceptable Solution F7/AS1, there must be at least one smoke alarm in every sleeping space or within 3 metres of a sleeping space entrance. There must also be an alarm on each storey where there is a habitable space.
Stand-alone battery-powered units can be used, but a much more reliable option is to use alarms that are permanently-wired to mains power with battery backup.
All residential rental properties are required to have smoke alarms – at least one in every sleeping space or within 3 metres of a sleeping space entrance. There must also be an alarm on each storey where there is a habitable space.
Meter boxes (for mains supply only) can be metal, fibreglass or PVC-U. In coastal areas, PVC-U, fibreglass or stainless steel are the best options.
Inside-opening boxes with only a window to the outside (through the cladding) are becoming more common – these need to be installed in a garage or utility area where the industrial look of the meter box is not out of place but good access is maintained.
The meter box must be:
- adequately flashed around the opening in the cladding (see E2/AS1 Figure 69)
- located for easy access
- located for easy digger access for mains cable excavation
- located centrally in the building for shorter internal cable runs
- located for a short mains cable route.
If added security to the power system is required, select a lockable meter box or install a lock. If lockable, the box must have a window for meter reading if a smart meter has not been installed.
By installing the meter box near its final position and including the builder’s earth leakage-protected power outlet in the meter box, the box can be incorporated into the house as construction work proceeds, and no additional metering or grid connection will be required.
Remote electronic reading of the meter or smart meter has largely replaced traditional meter reading – designers will need to check availability of such systems with the electricity retailer that the client will be signing up with.
The distribution board should be sized to cope with maximum demand and include allowance for future demand.
Locate the distribution board:
- centrally to keep cable costs and lengths, and voltage drop to a minimum.
- close to the area of highest demand, such as the kitchen, if possible.
- where it is visible and easily accessible in the case of an emergency
- so that it has no obstructions
- with good access to roof and floor spaces for maintenance or additional wiring installation
- in a well ventilated, dry area
- at least 1.2 m but no higher than 2.9 m above the floor.
Do not locate the distribution board under the stairs area if possible.
Domestic distribution boards are generally PVC-U or metal and flush-mounted in the wall. Larger boards, i.e. over 40 MCB capacity, should have a metal door.
Additional distribution boards may be required if a house is not easily wired from one distribution board such as if there is an interconnecting walkway, a courtyard or a garage. The additional sub-board or distribution board may be fed either from the main distribution board or from the main meter box.
Surge protection is required to protect systems against sudden power surges:
- Coarse protection provides protection to the electrical system against lightning or a major fault such as a surge from a grid malfunction or an accident. Coarse protection units are generally installed in the meter box.
- Medium protection provides protection from voltage surges or brownouts (low or under-voltage supply). Medium protection units are generally installed in the meter box or distribution board.
- Fine protection offers the best protection and is used to protect a specific appliance or group of appliances. It is also the most expensive option. It is typically a plug-in module such as an uninterruptable power supply (UPS). The appliance is not directly connected to the mains but only receives power from the UPS.
Additional individual circuit surge protection should be considered for under-tile heating, in-slab heating and solar power systems.
Residual current device (RCD) protection
An RCD is a portable or fixed electrical safety device which will immediately disconnect the power supply to an electrical appliance or tool when it senses a loss of current – this can happen when someone touches a live wire causing the power to flow through their body to the ground or an appliance or tool is faulty or damaged. There are three types of RCD:
- switchboard RCDs
- socket outlet RCDs
- portable RCDs.
All new lighting and power outlet circuits installed in electrical installations must be protected by one or more RCDs mounted on the main distribution board or the sub-board supplying the circuit. (This does not apply to permanently connected appliances.)
Earthing or equipotential bonding of metal components may be required where there is risk of an electrical fault causing metal components such as pipes, metal sinks and bench tops, metal shower trays or urinals and exposed structural steel work, to become live.
All circuits must be clearly labelled at the distribution board to identify the circuit and outlet.
As-built drawings should be supplied to the building owner that:
- indicate the extent of the installation
- identify the circuit
- indicate the location of the cables within concealed spaces (e.g. height from floor)
- indicate the location of all external cables and other electrical installations (e.g. a wind turbine).
BRANZ recommends that a photographic record of cable location is made during installation and supplied to the building owner with the as-built drawings.
Working on existing buildings
Establish the age and condition of the wiring and distribution board before starting work on an existing building. Some houses will have the fuses on the main board, and wiring consisting of rubber-sheathed wiring in metal conduit. If this is the case, the wiring is likely to be unsafe and should be replaced. Early installations of TPS (tough plastic sheathed) cable may also be in poor condition due to deterioration of the plastic sheathing and insulation.
Older houses may have lighting circuits where the supply cable from the distribution board is connected at the light fitting and then looped to another fitting (called three-plate wiring). In this configuration, even when the light is not switched on, the phase wire at the light fitting remains live.
Updated: 24 November 2020