Energy

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:

  • meter box
  • distribution board
  • surge protection
  • residual current device (RCD) protection
  • earthing
  • labelling
  • working on existing buildings.

There are also important considerations when working on existing buildings.

Meter box

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.

Meter boxes that are open to inside, with a window to the outside for meter reading are becoming more popular. These should be installed in a garage or utility area. Alternatively, locate the meter behind an aluminium window that is able to be opened from the outside.

The meter box must be:

  • adequately flashed around the opening in the cladding
  • located for easy access to read the meter
  • 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.

BRANZ recommends the meter box is located as far away as possible from sleeping areas, as AC power can have an effect on the human body.

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.

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.

In some areas of New Zealand, remote electronic meter reading or smart metering is replacing the traditional meter box.

Distribution board

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 –location in a cupboard is not recommended although it is permitted by AS/NZS 3000, 2.9.2.5 with special design criteria
  • 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 30 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

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.

Residual current device (RCD) protection

An RCD is an electrical safety device that will disconnect the power supply when it senses a loss of current. 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

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.

Labelling

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.

More information

RCDs