Inverter Topologies and DC System Grounding

When it comes to troubleshooting ground faults in solar systems, understanding inverter topologies is absolutely essential for both safety and efficiency. These fundamental topology differences don’t only affect how power flows through your system – they completely change how ground fault protection works, what safety hazards exist, and how you approach troubleshooting in the field. This video excerpt comes from Solar Tech Collective’s comprehensive course “Solar PV Ground Fault Troubleshooting: Theory, Tools, and Field Application,” where industry experts Brian Mehalic, Alex Jahp, and Rebekah Hren break down the critical differences between transformer-based and transformerless inverter designs.

It doesn’t matter if you’re dealing with an older string inverter with transformer-based isolation or a modern transformerless system, each topology requires a different troubleshooting strategy and safety approach. In the full course, you’ll learn how system grounding configurations have evolved over time, from the pre-2010 “grounded” systems to today’s “functionally grounded” designs, and why understanding these distinctions is essential for any technician working on energized PV systems. 

If you’re ready to master these concepts and learn the systematic approach to ground fault troubleshooting that can save you hours in the field, enroll in the full course to access all twelve modules of expert training and practical field applications.

Transcript below.

 In order to safely and efficiently troubleshoot, locate, and repair DC ground faults, it’s essential that you understand the inverter topologies, and DC system grounding configurations that you’re going to come across out there in the field. 

Let’s get started by simply introducing two key concepts- inverter topologies and DC GFDI.

What is an inverter topology? 

Topology refers to an inverter’s electrical configuration and design. From one topology to another, system grounding and protective devices vary. When these things vary, it impacts inverter operation, troubleshooting processes, and our safety as technicians out there in the field doing the work.

A PV DC GFDI is a ground fault detector interrupter. GFDI attempts to make PV systems more safe by detecting ground faults and interrupting the flow of current. All inverters are going to have a listed DC GFDI as it’s an NEC requirement, and it’s typically going to be integrated into the inverter. GFDI functionality varies between inverters, as it depends upon the inverter’s topology and its age.

To properly understand what DC GFDI is, we need to look at the requirements that apply to it in the NEC. The NEC has two main requirements for it. It says that it needs to control faulted PV system DC circuits by either automatically disconnecting current-carrying conductors of faulted circuits, or by automatically ceasing supply of power to the output circuits of the device fed by the faulted circuits and interrupting their ground reference.

Regardless of how it controls faulted circuits, GFDI protection equipment must provide indication of a fault at a readily accessible location. Examples of how this is done include remote indicator lights, displays, monitors, or alarm systems, and notifications by web-based service.