ASB Confirms Compliant Cable Sizing for Fox ESS KH 8 to 10kW Inverters Under Latest Installation Manual

Recently, Aussie Solar Batteries (ASB) has experienced a significant surge in installations across Australia. In response to questions raised within the industry, we are providing a clear technical update regarding grid port and backup port cable sizing for Fox ESS KH 8kW and KH 9.9 to 10kW inverters.

For the latest datasheets, please refer to the official Fox ESS website.

Installation Manual Update and Timeline

Following installation guidance provided by ASB in September 2025, Fox ESS officially updated the KH series installation manual in October 2025.

All manuals and quick guides released prior to October 2025 are now obsolete.

ASB’s cable sizing and installation methods fully comply with:

• Fox ESS factory requirements
• The updated official installation manual
• Australian electrical standard AS/NZS 3008

Why Installation Methods Differ Internationally

When Fox ESS entered markets such as South Africa and Pakistan, where daily power outages are common, installers often connected all household loads directly to the EPS backup port.

This allows the entire home to run from the inverter during outages.

However, this approach differs significantly from Australian best practice.

In those markets, systems may draw up to 16kW from the grid through the Grid Port on an 8kW inverter:

• 8kW supplying loads
• 8kW charging batteries simultaneously



This configuration is not suitable for Australian conditions.

Why This Method Is Not Used in Australia

1. Higher compliance costs

Full home backup requires Type A RCBO protection on every circuit, which increases installation costs significantly.

2. Reliability risks without a changeover switch

Without a changeover switch, inverter failure would cut power to all backup loads even if the grid is available. ASB installs changeover switches on all systems to eliminate this risk.

3. Grid infrastructure limitations

Many Australian homes, especially in regional areas, are limited to:

• 10 mm² mains cabling
• 50A main switches

Drawing 16kW continuously risks cable overheating, switch tripping, and network non-compliance.

ASB’s Installation Philosophy

ASB uses the configuration known as “Without EPS Function (External)”.

This means:

• Grid supplies loads directly when available
• EPS activates only during outages
• A changeover switch protects reliability

This approach is safer, more compliant, and better suited to Australian infrastructure.

Approved Cable Sizing

Under Fox’s updated October 2025 manual:

KH 8kW

10 mm² cable with a 40A breaker

KH 9.9kW and 10kW

10 mm² cable with a 50A breaker

This setup fully complies with Fox ESS requirements and AS/NZS 3008.

Why These Sizes Are Correct

Australian cable sizing follows a simple rule:

Cable capacity must be greater than or equal to breaker rating, and breaker rating must be greater than or equal to inverter maximum output current.

Example for the KH 10kW:

• Maximum AC current: 45.7A
• Circuit breaker: 50A
• 10 mm² cable capacity: 52A

Result: 52A > 50A > 45.7A

This is a safe and compliant design.

Larger cables and breakers are not automatically better. They only need to safely carry the inverter current with an appropriate margin. The correct fit is what matters.

Manual and Automatic Changeover Switches

Some customers use manual changeover switches.

After observing higher temperatures in certain automatic units, ASB trialled manual switches to compare thermal performance.

Functionally, both options are safe and reliable. Manual switches simply require human intervention during outages.

To date, ASB has received zero complaints related to changeover switches. ASB was also among the first companies in Australia to actively promote automatic changeover switch installations.

Installation Progress Across Australia

QLD

• Metro battery-only jobs completed
• Regional and PV plus battery underway
• Completion above 90%

NSW

• Within 300 km of Sydney above 98% complete
• Regional NSW above 80% complete
• Remaining rural jobs scheduled for completion by February

SA

• Approximately 60% complete, with near full completion expected by February

According to REC data, ASB ranked number one in Australia for battery installations in November and December 2025 and number one nationally for the full year 2025. Market share reached 9% in NSW and top three in QLD.

Looking Ahead to 2026

ASB will continue expanding across NSW, QLD, and SA.

Key updates include:

• Zero deposit promotion continuing until 31 March, subject to demand
• VIC operations launching from 1 May
• Focus shifting toward 14 to 28 kWh systems
• Larger 42 kWh systems expected to increase to AUD 13,000 to 15,000 after rebate changes

Customers considering larger batteries are encouraged to install before 1 May.

Our Commitment

ASB’s team includes specialists across inverter and battery research and development, sales, wholesale, retail, installation, and licensed electrical services.

The core management team has over ten years of Australian solar and storage experience. Over 90% of customers achieve zero or near zero electricity bills.

While rapid growth and high installation volumes present challenges, our goal remains the same. We deliver safe, compliant systems and work toward complete customer satisfaction.

We appreciate the community’s support and remain committed to raising the standard for battery installations across Australia.