The 2024 update to AS/NZS 4777.1, Grid connection of energy systems via inverters – Installation requirements, is one of the most substantial changes to solar and inverter installation procedures in Australia in over a decade. This new standard has been made mandatory for new installations from 23 February 2025. AS/NZS 4777.1 specifies the installation requirements for inverter-based energy systems, such as solar photovoltaic systems, battery energy storage systems, and other forms of distributed generation that connect to the electricity grid through an inverter.

These systems need to be able to function safely both for the customer’s installation and for the overall electrical network. This standard specifies the electrical connection requirements for inverters, the protection and control systems, the definitions and configurations for different types of supplies, and the requirements for disconnecting from the grid under abnormal conditions. This standard is to be used in conjunction with AS/NZS 4777.2, which specifies inverter performance requirements, as well as other Australian standards for electrical installations that relate to safety.

What Has Changed From Central Protection to Interface Protection?

One of the most important changes in the 2024 standard is the renaming and redefinition of the responsibilities of protection. The word “central protection,” which was used in the 2016 version of AS/NZS 4777.1, has been replaced by the word “interface protection.” Interface protection is the protective device or relay system that is installed between the site main switch and the inverter or inverters, downstream of the main switch but upstream of the inverter energy system.

The reason for its use is to identify abnormal conditions in the grid, such as voltage or frequency deviations, and to switch off the inverter before it can damage the grid or the installation. In essence, interface protection ensures that if the grid becomes unstable or a fault occurs, the inverter does not continue to feed power into the grid and make the problem worse. Before 2024, central protection was often confusing in terms of its location and function.

Which Installations Require Interface Protection?

However, as per the AS/NZS 4777.1:2024 standard, interface protection is only required for inverter energy systems with a total aggregate capacity above 200 kVA. This is a major shift from the earlier standard, where interface protection might be required for systems with capacities as low as 30 kVA. Systems with capacities below 200 kVA are exempt from the requirement for mandatory interface protection as per the national standard. However, this does not supersede the requirements of the local Distribution Network Service Provider (DNSP). Networks like Energex, Ergon, SA Power Networks, ActewAGL, and Ausgrid might require interface protection at lower capacities or set certain protection parameters.

What Functions Does Interface Protection Perform?

In cases where interface protection is required for the installation, the standard defines a list of protective functions to guarantee safe operation. These functions include over-voltage protection, under-voltage protection, over-frequency protection, under-frequency protection, and the rate of change of frequency. The protection system will disconnect the inverter when the grid is operating outside the normal range. For instance, over-voltage protection can occur at 267V with a maximum disconnection time of three seconds, while under-voltage protection for severe conditions can disconnect within twelve seconds at 69V. Over-frequency protection can disconnect in 1.5 seconds at 52Hz, and under-frequency protection in three seconds at 47Hz. Frequency rate of change protection can trip at a rate of plus or minus 4Hz/sec within one second. These values are consistent with AS/NZS 4777.2:2020 to guarantee predictable and safe inverter operation.

How Has Metering and Aggregation Changed?

The AS/NZS 4777.1:2024 standard has clarified metering and aggregation requirements. In the past, complex installation situations, like embedded networks or precincts, were considered on a case-by-case basis with different levels of protection required. However, the new standard has made it possible for these situations to be assessed on a case-by-case basis, sometimes in conjunction with the DNSP. In the case of large embedded networks or facilities with multiple installations, protection levels and conditions are determined with the network operator, and it is necessary that the designer and consultant be able to provide clear documentation of protection strategies, set points, and paths to compliance.

Why Does This Matter for Australian Projects?

The changeover to interface protection and the increased capacity threshold has several implications for solar and battery projects in Australia. For most commercial projects, the exemption of mandatory interface protection for projects below 200 kVA will result in cost savings, as there will be no need for additional hardware. Before the change, projects with capacities between 30 kVA and 200 kVA would require central protection gear.

The increased threshold now exempts most commercial rooftop solar and small utility-scale solar projects, although DNSPs can still set project requirements. The harmonization of terms and practices with international best practices will also make it easier for solar installers, switchboard manufacturers, and designers operating in the Australian and international markets.

How Should Interface Protection Be Designed and Implemented?

In the case of systems that need interface protection, it is important to involve the DNSP early to gain an understanding of connection needs, protection schemes, and documentation requirements. Protective schemes should reflect the voltage and frequency trip levels specified in AS/NZS 4777.2:2020 to provide predictable and safe system behavior during abnormal grid conditions. Documentation should clearly indicate the location of the interface protection device, relay programming, CT and VT configuration, disconnection logic, and sequence of events recording.

Documentation and standard compliance will help avoid commissioning delays and ensure smooth approval procedures. Installation work should also be carefully considered. Interface protection devices should be installed downstream of the site main switch but prior to all inverter connections. Factors to consider include cable routes, CT positioning, isolation access, and labeling to allow for safe maintenance and emergency shutdown.

Are There Other Key Changes in AS/NZS 4777.1:2024?

Protection of interfaces is not the only important change. The standard specifies phase balance limits for single-phase systems to avoid voltage imbalance on the local network. It also specifies a limit of two inverters’ main switches for installations with other loads on a switchboard, with larger systems requiring an aggregation board to enable all inverters to be switched off by a single main switch.

The standard specifies the requirements for Inverter Power Sharing Devices, which are required when more than one installation shares a single PV generation resource, such as in apartment buildings. It also supports Vehicle-to-Grid systems and advanced electric vehicle supply equipment, allowing these to safely export power under controlled conditions.