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Technical Advice for Alternative Power Supplies

Usually when the power goes off; it’s not too long a few hours maybe –  before it’s restored. Inconvenient, but mostly we can manage. But in the aftermath of a natural disaster; it may be some days or weeks before normal supply is reinstated. There will be huge pressure to get some sort of power supply running.  Freezers need to be kept cold, cell-phones need to be recharged. And now that copper telephone lines have largely ben replaced with fibre optic cable; old-fashioned landlines don’t work unless you can plug the modem into a power socket.

Energy Safety have released a technical bullitin on connecting a genertaor to the wiring of a house or buidling following an emergency. Click here to view

This allows for generators to be connected to an installation in a normally non-compliant manner as emergency relief following flooding, and cyclone Gabrielle.

 The below information and advice covers using other sources of supply to keep essential items running; until such time as normal supply is restored.

The guidance is only to be used in affected areas for emergency relief, and only if there is no other compliant option available.

The Energy Safety bulletin must be followed explicitly, and its use recorded on any COC.

As of March 2023; we have three options when connecting generators. 

Fully compliant alternative supply

As time goes by, and things start to return to normal, we’ll see increased demand for this sort of work; but unfortunately, it’s not as simple as just connecting a genset. There are a number of issues; but the fundamental problem is that most portable generators are simply not suitable for connection to an installation that’s set up for supply from the MEN distribution system used in NZ (and Australia).

We have a ‘Quick Generator Guide’ which can be found here

The ONLY sort that is, is one that has NO connection between the generator’s winding and the frame / earth. This is known as an ‘isolated output” generator.

The general requirements for using any form of generation to supply an installation are in Clause 7.3 of AS/NZS 3000; and the details for using a generating set are in AS/NZS 3010: 2017.

  1. the generator can be connected permanently by fixed wiring, following Sections 2 & 3 of the Standard.
  2. Provision can be made for temporary connection using a “detachable connection (eg plug & socket, or appliance inlet); following Sections 2 & 4.

 With regard to the Standards:

  • for “3000”; ESRs require compliance with 2007 edition including Amendments 1 & 2
  • for “3010″; ESRs specify the 2005 edition – but only for “mains parallel” installations. But what we’re dealing with here is not “mains parallel; it’s an “alternative supply; so, the version to use is the latest one (2017 inc A1)

If the installation is already set up with a permanent genset; job done.

If it’s set up with an inlet or lead ready for a genset to be plugged in, your only problem will be finding a suitable – i.e. isolated output – genset.

But if provision isn’t already there; it’s probably not feasible to adopt this option during an emergency.

Temporary supply direct to equipment

This is the simplest – and cheapest – option.

It’s just a matter of locating a genset, putting it in a suitable, well-ventilated place (NEVER inside a building that wasn’t designed as a generator house); and using extension cords to get a supply to essential appliances.

There’s some guidance in this in Appendix B of AS/NZS 3010: 2017; and more in Section 3 of AS/NZS 3002. “3002″; which covers Shows & carnivals.  While an emergency supply to a house or business is not a ‘show” or a “carnival”; this Standard is also untended and used for scout jamborees, army camps, and civil defence shelters. So, despite the title; it’s exactly what we want for emergency work after a natural disaster.

Specifically, Section 3, which covers “event wiring”; which can be assembled by unskilled persons. This is not PEW; so, doesn’t need to be installed by licenced electrical workers – and there’s no certification needed.

Simply check that the equipment you’re using is safe – e.g. current test tag -; then apply common sense.

Emergency supply following Worksafe’s special guidance

Worksafe have published a guidance document (“technical bulletin”; or TB for short) providing for short-term connection of a genset to an installation in an emergency.

Available here and can be downloaded as a PDF.

What counts as an “emergency”?

The TB doesn’t specify. But what caused Worksafe to issue it is the expectation that it will take a long time to get distribution networks restored in the east coast of the North Island after the devastation caused by Cyclone Gabrielle. So, we can assume that it requires a similar level of disruption by natural disaster before we can use it.

Basically, the guidance in the TB covers

  1. disconnection & making safe of the normal supply mains at line side of main switch.
  2. modification of the installation, and the generator if required, to make them compatible and provide a safe supply
  3. connection of the generator, in place of the normal mains; to provide a short-term source of supply.
  4. certification requirements
  5. reinstatement requirements

It’s important to realise that following the TB’s guidance will result in an installation that does NOT comply with the Electricity (Safety) Regulations. It should be functional; and it should be safe. But it will not be compliant. And there’s nothing in writing – not even an email – to say people who follow it won’t be prosecuted. However, they would certainly look very foolish in the court of public opinion if they prosecuted someone who followed this official document – provided it was done for the intended purpose of emergency supply following Cyclone Gabrielle or similar emergency. And provide it was followed exactly

An outline of the TB’s guidance (as at 8/3/2023) is below. There are significant safety issues with this sort of work; so, DON’T rely on this outline alone. Go to the website and download the official document. It’s very important that this TB is followed to the letter, with absolutely no deviations.

The problem is that most small gensets available are intended for direct supply to equipment; and are NOT suitable for connection to an MEN installation.  So, in order to get a short-term supply, either the genset needs to be altered, or the installation does; or both. Worksafe have opted for altering the installation in every case; and the guidance gets around this by allowing for use of;

  1. an RCD-protected genset; or
  2. a centre-tapped genset in conjunction with an RCD; or
  3. an isolated-output genset, modified to provide a polarised output.

In all cases:

  • the incoming mains – A(s) & N – must be disconnected at main switch (line side)   and the N-bar; & terminated safely;
  • a (compliant) genset is connected to the main switch;
  • load must be reduced so that the max demand does not exceed the rated capacity of the genset;
  • the installation’s MEN link must be removed – unless adopting the option of setting up a “standalone” installation (see below) (any others, eg at DBs,  must also be removed; though that’s not stated);
  • the fact that these alterations have been made must be clearly labelled at the MSB;  and
  • the work must be certified, including stating that the work was done in accordance with the Worksafe guidance.
  • no inspection required, even though it’s ‘mains work”; because they’ve declared this work to be classified as “general PEW”.
  • “larger” connections require design by an Inspector or Electrical Engineer.

Alternatively; the TB specifically allows us to set the installation up as a stand-alone installation in accordance with AS/NZS 4509.1 .  In which case we will NOT be removing the installation’s MEN link, nor making any N-E connections within the genset; just disconnecting the normal mains and connecting a generator that has an isolated output. This is probably the best option for a multi-phase installation.

Connection Capacity

Selecting the generator

Disconnection of mains

Removing the MEN link

Checking the main earthing system

Locating the generator

Connecting the generator

Installation with inverters

Limiting maximum demand



What type of generator do I have?

The fastest way to check what type of generator you’re working with is to fire it up before connecting it and testing the output with a voltmeter. It’s best to do this with some load connected; to eliminate stray voltages that can occur under no-load conditions. Load also steadies the voltage, which is likely to be on the high side with no load.


RCD-protected gensets are obvious. They have an RCD built into them as supplied from the factory. And to enable the RCD to operate as intended; they have a connection between neutral and “earth” made upstream of the RCD. This connection may be a simple link and may even be removable. Or for generators with an inverter output, it may be made within the inverter stage. The frame will also be connected to the “earth”.

Bearing in mind that it isn’t really “earth” at all, as it isn’t connected to the mass of earth. It’s actually an “equipotential bonding system”; but most people think of it as “earth” because it’s connected to the “earth” terminals of the output

The output, as measured with a voltmeter, will look like a normal (MEN) supply:

A – N :   230 V A – E :    230V N – E :   0 V

Centre-tapped “single phase”

Many, especially older, small portable gensets are this type. Basically the winding is in two halves, with a connection to frame / “earth” made at the mod-point. As a result, they are not actually a single-phase genset at all; the output is actually 2-phases with 180 degrees phase angle between them; and there’s no neutral. What looks like a neutral is and is connected to the “neutral” terminal of any 230V socket, is actually Phase 2.

The output, as measured with a voltmeter, will be:

A – N :   230 V A – E :    115 V N – E :   115 V

Isolated output

With this type, there no connection between the winding and frame / earth. But it would be unwise to test this using an insulation resistance tester; as there may be suppressors or other electronic components that could be damaged by the test voltage.

The output, as measured with a voltmeter, looks the same as from an isolating transformer:

A – N :   230 V A – E :    0 V N – E :   0 V

For 3-phase, there will be 400 v between phases; with each phase generated by a separate winding, and neutral being the star point where the 3 phase winding are connected together