Introduction to Summation of Supplies - CPD449

Solar inverters used to be small. Battery systems were rare. EV chargers barely existed. Switchboards were designed for one thing: a single grid supply flowing in one direction. That world is gone — and the switchboards being asked to manage solar, batteries, and EV chargers today were never designed for it.

This course tackles one of the most misunderstood compliance requirements in modern solar and battery installation work: the summation of AC currents. When you add a supplementary supply to a switchboard, you're not just offsetting load — you're introducing current that the overcurrent protection on the main switch will never respond to. Cables and busbars that were perfectly rated before can become non-compliant the moment an inverter is connected. Installers are picking up defects because of this, and most of them didn't see it coming.

Presented by Pat Southwell — licensed electrical inspector and solar industry professional — this course walks you through a clear, four-step process for assessing any switchboard containing supplementary supplies. You'll work through real installation scenarios covering compliant and non-compliant configurations, overloaded cables and busbars, current limiting solutions, and safe isolation in multi-supply switchboards.

By the end, you'll know exactly how to identify a summation issue, what to do about it, and how to make sure your installations don't end up on the wrong end of an inspection.