What is a DC Ground Fault in a PV System?

By Will White, Fluke Senior Application Specialist, DER

In any photovoltaic (PV) system, safety and uptime depend on proper grounding and fault detection. But when insulation breaks down or conductors come into contact with grounded components, DC ground faults can occur, introducing serious risks to people, equipment, and productivity.

A DC ground fault is one of the most common, yet often misunderstood, failures in solar installations. This article will walk you through what a DC ground fault is, how it occurs, why it matters, and where to go next if you're dealing with one in the field.

What is a Ground Fault?

A ground fault is an unintentional electrical connection between a current-carrying conductor (such as a DC positive or negative wire) and a grounded surface, usually metal parts like module frames, racking, or conduit.

On the DC side of a PV system, this typically means a positive or negative conductor is making contact with the equipment grounding conductor (EGC) or other grounded metal surfaces.

In AC circuits, a ground fault can occur on any ungrounded conductor (L1, L2, L3), but DC ground faults are specific to the photovoltaic (pre-inverter) side of a solar array.

Where Do DC Ground Faults Happen?

DC ground faults are most likely to occur in these areas:

• At the module: A damaged or pinched wire touches the module frame.
• In the combiner box: Insulation breakdown inside terminals or junctions.
• Along the homerun conductor: Vibration or thermal expansion causes wear inside the conduit or cable tray.
• During installation: Sharp racking edges, poor routing, or fasteners pinch or abrade conductors.
• In wet conditions: Water intrusion can bridge connections between conductors and grounded parts.

These issues can be difficult to detect immediately, which is why ground fault protection is mandatory for all photovoltaic (PV) systems under the National Electrical Code (NEC) and International Electrotechnical Commission (IEC) standards.

What Does a DC Ground Fault Look Like Electrically?

Electrically, a ground fault changes the voltage profile of a PV string or array. Normally, there should be zero volts between either conductor and ground. But when a fault is present, you'll measure a non-zero voltage between one or both conductors and ground.

You'll also still measure the expected open circuit voltage (Voc) between the positive and negative DC conductors. This is what makes ground faults deceptive—the array may appear to be producing power normally even while a dangerous fault is present.

How Do Ground Faults Occur?

DC ground faults are typically caused by:

• Mechanical damage: Conductors pinched during installation or movement
• Environmental stress: UV degradation, temperature cycling, moisture ingress
• Insulation failure: Aging, heat, or improper wire stripping
• Rodent damage: Animals chewing through wiring in conduit or junctions

In many systems, faults develop slowly. An intermittent contact may go unnoticed until it becomes a hard ground fault that trips the inverter or causes visible damage.

Why DC Ground Faults Are Dangerous

DC ground faults aren't just inconvenient, they're potentially dangerous. Low-current faults, especially in large PV systems, often go undetected, allowing time for conditions to worsen.

If a second ground fault develops on a different conductor, it can create a parallel path for current, which can lead to:

• Arcing faults
• Electrical fires
• Arc flashes at high voltage
• Severe equipment damage

In fact, a 2009 rooftop fire in Bakersfield, California, was caused by exactly this scenario—a small initial ground fault became a conduit for over 300 amps of current during a second failure. The result was a melted conductor, blown insulation, and a major fire.

To learn more about the risks, read: Why DC Ground Faults Are Dangerous

How Are DC Ground Faults Detected?

Inverters are required to include Ground Fault Detection and Interruption (GFDI) or Ground Fault Protection (GFP) devices, which detect faults and turn the inverter off. However, their effectiveness depends on system design:

• Transformer-based inverters often use fuse-based GFDIs, which may not detect faults below a few amps.
• Transformer-less inverters use residual current detectors (RCDs) that can sense fault currents as low as 300 mA.
• Module-level power electronics (MLPEs), such as optimizers and microinverters, often include built-in ground fault detection at the module level.

What Happens After a Ground Fault Is Detected or Suspected?

When a ground fault is suspected or an inverter shuts off due to GFDI activation, the next step is to locate the source and repair it safely.

You can follow these detailed guides to act:

• How to Test PV Strings for Intermittent Ground Faults
• How to Test De-Energized PV Circuits for Ground Faults
• How to Use Voltage Readings to Locate Ground Faults in Solar PV Arrays
• How to Test for Hard Ground Faults in PV Systems
• How to Repair Ground Faults in PV Systems

The Role of Grounding in Fault Prevention

Proper system grounding is your first line of defense. Here are the key NEC-defined components in a grounded PV system:

• Equipment Grounding Conductor (EGC) – Bonds all metal parts and provides a path for fault current
• Grounding Electrode Conductor (GEC) – Connects the system to earth ground (usually via a driven ground rod)
• Functionally Grounded Conductor – A current-carrying conductor that's intentionally grounded in a system, typically the negative conductor

When a ground fault occurs, current leaks from the intended circuit and flows through the EGC. This is why proper bonding, termination, and conduit layout are crucial to the long-term health of the system.

Are All Ground Faults the Same?

No. There are two primary types of DC ground faults:

• Hard Ground Faults – A sustained, low-resistance connection that persists continuously.
• Intermittent Ground Faults – A high-resistance connection that may appear only under specific conditions (e.g., rain, temperature changes, tracking array movement).

Want a deep dive on the differences? Read: What is the Difference Between a Hard and Intermittent Ground Fault?

Future Technologies and Prevention

Newer technologies are helping reduce the frequency and severity of ground faults:

• Transformer-less inverters that detect low-level leakage
• MLPEs that isolate faults at the module level
• Automated insulation resistance testing during system startup or daily operation

Summary

A DC ground fault is a critical issue in PV systems where a conductor unintentionally contacts a grounded metal surface. It can lead to undetected current leakage, dangerous arc faults, or even fires.

Understanding what a ground fault is—and how to identify, isolate, and repair it—is fundamental for every solar technician and system designer. Fortunately, with a structured approach and the right tools, ground faults can be diagnosed safely and efficiently.

About the Author

Will White began working in solar in 2005 for a small integrator. After starting as an installer, he worked in sales, design, and project management, and he eventually became the Director of Operations. In 2016, he joined the curriculum team at Solar Energy International (SEI), where he focused on developing course content and teaching solar classes. In 2022, Will moved into a solar application specialist role at Fluke, where he supports their renewable energy testing equipment like IV-curve tracers, electrical meters, and thermal imaging cameras.

Will has experience in wind power, solar thermal, energy storage, and all scales of PV. He is passionate about implementing high-quality, code-compliant installation techniques. Will has been a NABCEP Certified PV Installation Professional since 2006 and was previously a NABCEP Certified Solar Heating Installer. He has a B.A. in business management from Columbia College Chicago and an MBA from the University of Nebraska-Lincoln. In his free time, he can be found working with his wife and daughter on their homestead in central Vermont, which features an off-grid straw-bale house.

Connect with Will on LinkedIn.