EIS 008: Multiple Mode Inverters – RCD protection requirements

Background

Stakeholders from the renewable industry approached Energy Safe Victoria – seeking to clarify RCD requirements when installing a Multiple Mode Inverter (MMI).
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

An MMI with a stand-alone/backup port – which can provide backup 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 stand-alone/backup power, 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 AS/NZS 3000:2018 Clause 1.4.8.

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

AS/NZS 3000:2018 Clause 2.6.3.2.5 states Additional protection by RCD’s shall be provided in existing electrical installations where alterations or a switchboard replacement is completed.

When RCDs are installed to protect circuits to be supplied from a stand-alone port of a multiple mode inverter, 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 inverter manufacturer.

Therefore, any circuit(s) altered to be supplied by a stand-alone/backup supply shall have suitable RCD protection provided, as per AS/NZS 3000.

Note: If the switchboard is arranged to provide partial back up, 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.

Requirements:

AS/NZS 3000:2018 Clause 2.6.3.2.5 specifies the requirements to ensure RCD protection is provided to existing installations where alterations occur.

AS/NZS 4777.1:2019 Clause 5.4.4 specifies that RCD protection shall be installed on final subcircuits supplied from a stand-alone / back up port of a MMI, in accordance with AS/NZS 3000.

Note: AS/NZS 4777.1 is currently in draft format at the time of writing this information sheet. The new version of the standard will clarify the wording to clearly describe the requirements in this information sheet.

In summary

If any circuits have been altered to be backed up by the 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 – but it’s not mandatory to have RCDs installed, as these circuits have not been altered.

Relevant rules

Australian Standards

AS/NZS 3000:2018 The Australian/New Zealand Wiring Rules

Clause 2.6.3.2.5 Alterations to installations and replacement switchboards (Australia only)
AS/NZS 3000:2018 Clause 2.6.3.2.5 Alterations to installations and replacement switchboards (Australia only)

Additional protection by RCD’s shall be provided in existing electrical installations where alterations or a switchboard replacement is completed.
(a) Alterations: 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 4777.1:2016 Grid connection of energy systems via inverters Part 1: installation requirements

Clause 5.4.4 RCDs on multiple mode inverter system final subcircuits
RCD protection shall be installed on final subcircuits in accordance with AS/NZS 3000.
When RCDs are installed to protect electrical installation connected loads on a stand-alone port of a multiple mode inverter, 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.