Introduction to Summation of Supplies

Cables and busbars that were correctly rated for a single grid supply can become non-compliant the moment a second supply is connected. This course shows you how to assess a switchboard for the summation of AC currents under AS/NZS 4777.1 before it becomes a defect.

Solar, batteries and EV chargers all add current to a switchboard that was designed around one supply. It’s one of the most common compliance issues inspectors find, and one of the least understood — because the board looks exactly the same as it did before the inverter went in.

This course walks you through a four-step assessment you can apply on any job, using real installations with both compliant and non-compliant configurations. You’ll learn when current-limiting devices are the right fix, how to isolate a multi-supply switchboard safely, and what the labelling has to say once more than one supply is present.

What you’ll learn

• Why combining supplies can overload cables and busbars that were correctly rated
• A four-step process for assessing summation of supplies under AS/NZS 4777.1
• How to recognise an overloaded board from the wiring in front of you
• When current-limiting devices are the right solution
• How to isolate and label a switchboard with multiple supplies

Course content

Why summation of supplies matters

What changes on a switchboard when a supplementary supply is added, and the standard that governs it.

The four-step assessment

Working through supply ratings, conductor ratings, protection and the arithmetic that decides compliance.

Real installations, compliant and non-compliant

Walkthroughs of switchboards with solar, battery and EV charging, and what makes each one pass or fail.

Current-limiting devices, isolation and labelling

When a limiting device is appropriate, how to isolate a multi-supply board safely, and the labels that must be present.

This course includes

• 15 CPD points (SAA accredited)
• 30 minutes of on-demand video
• Certificate of completion
• Real-world switchboard examples

Your presenter

Pat Southwell — Licensed Electrical Inspector

Pat inspects solar and battery installations across Victoria every week as a Licensed Electrical Inspector, with more than 7,000 inspections behind him. He co-hosts the Solar Sidekicks podcast and has trained over 1,000 installers through Southwell Solar Training.