Multiple Mode Inverters – RCD protection requirements

Requirements

This guidance relates to installation and safety requirements that must be carried out by Registered Electrical Contractors (RECs) and Licensed Electrical Workers (LEWs) to ensure a safe and compliant battery system installation. LEWs and RECs have various legal obligations to install, be responsible for installation and inspect electrical work and equipment safely under the Electricity Safety Act 1998 (the Act) and the Electricity Safety (General) Regulations 2019.

This guidance is also relevant to Licensed Electrical Inspectors (LEIs) to ensure the completed installation is tested and verified in accordance with the Act and regulations.

As part of this legislative framework, the following Australian Standards are applicable to multiple mode inverters (MMI) – residual current device (RCD) protection requirements:

• AS/NZS 3000:2018 Electrical installations (the Wiring Rules)
  • Clause 2.6.3.2.5 specifies the requirements to ensure RCD protection is provided to existing installations where alterations occur. Note that this clause is only applicable in Australia (not New Zealand).
  • Additional protection by RCDs shall be provided in existing electrical installations where alterations or a switchboard replacement is completed.
  • For alterations to existing installations, RCD protection shall be provided as required by clauses 2.6.3.2.2, 2.6.3.2.3 or 2.6.3.2.4 as applicable to the type of installation.
• AS/NZS 4777.1:2024 Grid connection of energy systems via inverters, Part 1: Installation requirements
  • Clause 5.3.6.4 specifies that RCD protection shall be installed on final subcircuits supplied from a stand-alone/backup port of a MMI, in accordance with AS/N ZS 3000.
  • When RCDs are installed to protect electrical installation connected loads on a stand-alone port of a MMI, they shall be of a type that correctly operates on the standalone port output waveform and be in accordance with the requirements specified by the manufacturer for use with the inverter.

This page provides technical guidance about the applications of these standards. The full text of the Australian Standards can be purchased from the Standards Australia store.

Background

There are many installation methods used to connect MMIs with battery systems to a property's switchboard. These will depend on the owner's requirements, such as:

• full backup capability of the entire property in the case of a grid supply outage
• partial backup, such as lighting and some power circuits to maintain power to a fridge or water pump
• single circuit backup, such as one essential power circuit, determined by the owner.

Hazard

A MMI with a stand-alone/backup port – which can provide alternative supply power during a grid supply outage – doesn't provide adequate protection against fault currents. This includes an earth leakage fault occurring in the connected final subcircuits.

There are also hazards related to altered pre-existing RCDs. When those circuits have been altered to be supplied from an alternative supply, the pre-existing RCD's may not be the correct type – making them unsuitable for the new source of supply. In these cases, they may not operate correctly when an earth leakage fault occurs.

Energy Safe’s Position

An ‘alteration’ is defined in clause 1.4.8 of AS/NZS 3000:2018 Electrical installations (the Wiring Rules).

Altering the source of supply to circuit(s) is deemed to be a modification to part(s) of an electrical installation.

Clause 2.6.3.2.5 of the Wiring Rules states: Additional protection by RCDs shall be provided in existing electrical installations where alterations or a switchboard replacement is completed.

Clause 5.3.6.4 of AS/NZS 4777.1:2024 for grid connection of inverter energy system (IES) states that all circuits supplied by the alternative supply shall conform with AS/NZS 3000 requirements for protection and RCDs. All existing circuits that are being connected to the alternative supply from an IES are deemed to be an alteration to the electrical installation for the purposes of AS/NZS 3000.

When RCDs are installed to protect circuits to be supplied from a stand-alone port of a MMI, the RCDs shall be of a type that correctly operates on the alternative supply port output waveform and be in accordance with the additional requirements specified by the inverter manufacturer for use with the MMI.

Therefore, any circuit(s) altered to be supplied by an alternative supply shall have suitable RCD protection provided, as per the Wiring Rules.

Note: If the switchboard is arranged to provide partial backup, only those circuits that are supplied from the stand-alone output port of the MMI are deemed to be altered. All other circuits may remain as the same.

Summary

If any circuits have been altered to be backed up by a MMI installation, those circuits need to be provided with RCD protection. Use the correct RCD type as specified by the inverter manufacturer.

If there are no RCDs on the existing non-backed-up circuits, it’s preferable to provide RCD protection. However, it’s not mandatory to have RCDs installed, as these circuits have not been altered.

Disclaimer

The above guidance provides practical and technical guidance. It does not constitute legal advice. Licensed electrical workers, registered electrical contractors and licensed electrical inspectors should seek independent advice about their obligations under the Electricity Safety Act 1998 and the Electricity Safety (General) Regulations 2019.