A new technical report, SNZ TR 6120:2014 Low voltage supply earthing systems, investigates alternative options to the multiple-earthed neutral (MEN) system of low voltage earthing currently used in New Zealand.
The report investigates five alternative earthing systems and recommends that the International TT system of supply should be considered in particular circumstances. The MEN system currently used in New Zealand has limitations, especially in remote rural areas, and the TT system would offer improved safety and performance.
SNZ TR 6120 is an informative document until the TT system is approved in the Electricity (Safety) Regulations for use in New Zealand. At that stage, the report will provide background information to enable decisions to be made on whether the MEN or TT systems should be used in any particular circumstance. It is unknown at this stage whether the regulator or the electricity supply companies will make these decisions.
Before the TT system can be used, an amendment to AS/NZS 3000:2007 Electrical installations (known as the Australian/New Zealand Wiring Rules) will need to be developed to cover the different rules for the TT system. This work will take place over the next 12 months.