The industry has seen rapid uptake of solar PV and energy storage systems connected to multiple mode, or ‘hybrid’, inverters and battery systems over recent months. This has prompted many questions from installers and designers regarding the connection of inverter energy systems to existing electrical installations. While many common questions regarding connecting IES systems can be clarified by consulting AS/NZS3000:2007 Section 7.3 Alternative Generation Systems, complexity is introduced with the release of AS/NZS4777.2:2015 Grid connection of energy systems via inverters (Part 2: Inverter requirements), and AS/NZS4777.1:2016 Grid connection of energy systems via inverters (Part 1: Installation requirements). GSES wishes to highlight a few key requirements of AS4777.2, which came into effect on October 9th 2016.
Maintaining continuity of the grid neutral in multiple mode inverter installations.
Whilst the switching of incoming neutral has never been allowed at the main / MEN switchboard and has only been allowed in extremely limited situations at downstream distribution boards (refer to AS/NZS3010 Electrical Installations – Generating Sets for details), AS4777.2 now explicitly states the requirement of continuity of grid neutral-earth connection (MEN connection) must be maintained at all times. There is a good reason for this. If the multiple mode inverter disconnects the stand-alone port neutral conductor from the main installation neutral when it switches to stand-alone mode, it will remove both the earth reference required for RCDs (whether RCCB or RCBO) to operate in earth leakage mode, and the low impedance return path required for short circuit protection devices – fuses and circuit breakers (whether MCB or RCBO) to operate in the event of a live conductor coming into contact with an earthed metallic part of the installation. Clearly this becomes a shock hazard and must be avoided at all costs. It is critical for the installer to ensure that the load neutral to MEN connection is maintained during all operating modes of the inverter, including stand-alone mode.