Generator Connection Switches

Today, it is not only plant such as chillers and freezers that require auxiliary power during a mains failure, as everyday operations across farms, orchards, vineyards, small business and homes rely on electricity for basic communication and operational functions – for example home based medical equipment. Computers are everywhere and the facility to connect a stand-by generator has become a frequent requirement for many businesses and homeowners.

The prescribed connection of both permanent and temporary generators is covered by the electrical standard AS/NZS 3010 which should be referenced in all instances. The following information is taken from the standard, however is not a complete and full summary and does not replace the standard.


The purpose of a Mains Off Generator switch is to safely enable a load to be supplied by either Mains Power or Auxiliary Power - and ensure only one source can be connected to the load at any time.  An Off position to isolate the load from either power source is a very popular option, for maintenance of the load, for example. In reference to "standard" Single Phase or Three Phase and Neutral installations, all phases are switched on both the Mains and Generator sides. However, as New Zealand installations employ a MEN (Multiple Earth Neutral) connection at the Main board, the Neutral on the Mains side must not be switched - it must be permanently connected.

Conversely - the Neutral from the Generator supply is always switched, unless it is also permanently connected to the Neutral bar at the Main board. There are exceptions with some installations and AS/NZS 3010:2005 should be referenced for all details.

Very Importantly - in Three Phase applications, the switch must be designed such that when switching to the Generator supply, the Neutral from the Generator supply is connected (contact closed) before the Phases from the generator are connected (contacts closed); inversely when switching back to OFF from Gen, the Neutral contact opens only after all Phases are disconnected (contacts open).

In Single Phase applications, the Neutral contact shall open and close simultaneously with the Phase contact.

Connection Diagrams according to AS/NZS 3010:2005

Please refer to the following diagrams for Single Phase and Three Phase installations.

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