Residual Current Device (RCD) protection in Battery Energy Storage Systems (BESS)

Purpose

The purpose of this advisory note is to inform industry of common non-compliances identified by Building Commission NSW inspectors during inspections of Battery Energy Storage Systems (BESS) with alternative (back-up) supplies.

Issue

Lack of Residual Current Device (RCD) protection in BESS installations.

References

• AS/NZS 4777.1:2024 Clause 5.3.6.4.
• AS/NZS 3000:2018 Clause 1.9.3.1, 2.6.2.2.2 and 2.6.3.2.2.

Identified non-compliant practices

Lack of RCD protection for circuits supplied by alternative supply

During inspections of BESS, it was observed that in certain installations, final subcircuits supplied by the new alternative (back-up) supply were not protected by RCD. 

This practice does not comply with the requirements stipulated in Clause 5.3.6.4 of AS/NZS 4777.1:2024 and Clause 2.6.3.2.2 of AS/NZS 3000:2018, both of which mandate RCD protection for final subcircuits irrespective of the supply source. 

Use of Type Alternating Current (AC) RCDs instead of Type A RCDs

In accordance with AS/NZS 4777.1:2024, the addition of an alternative supply is considered an alteration to the electrical installation. Under AS/NZS 3000:2018 Clause 1.9.3, any alteration requires all associated parts of the installation to be brought into compliance with the current standard. 

The use of a Type AC Residual Current Device (RCD) in this configuration does not meet the requirements of Clause 2.6.2.2.2, which mandates the use of Type A RCDs. Type A RCDs must be marked with the following symbol:

Note: AS/NZS 3000:2018 Clause 1.4.8 defines 'Alteration' as 'a modification to part(s) of an electrical installation.'

How to comply with the standards

AS/NZS 4777.1:2024 Clause 5.3.6.4

All circuits supplied by an alternative supply must comply with the requirements of AS/NZS 3000:2018. The addition of an alternative supply is deemed an alteration to the electrical installation for the purposes of AS/NZS 3000:2018. 

AS/NZS 3000:2018 Clause 2.6.3.2.2

Additional protection by RCDs with a maximum rated residual current of 30 mA shall be provided for all final subcircuits in domestic and residential electrical installations. Where protection of final subcircuits is required, RCDs shall be installed at the switchboard where the final subcircuit originates.  

AS/NZS 3000:2018 Clause 1.9.3.1

When alterations are made to an electrical installation, all parts of the installation affected by the alteration must be upgraded as necessary, so they meet current standard requirements. 

General application

When an alternative supply is added to an installation, all circuits it supplies must be brought up to the current wiring rules. 

Any alteration must ensure that all associated parts of the installation are upgraded as necessary, with protective devices, wiring, and connected equipment suitable for the characteristics of the new supply arrangement. 

In domestic and residential installations, this includes ensuring all final subcircuits are protected by RCDs with a maximum rated residual current of 30 mA.