How to Locate Hard Ground Faults in Solar PV

By Will White, Fluke Senior Application Specialist, DER

A ground fault in a solar PV system can significantly impact energy production, trigger inverter shutdowns, and present safety risks. Often, the first indication is a tripped Ground Fault Detection Interruption (GFDI) or inverter fault notification. In either case, time is critical, and you need to verify the fault, pinpoint its location, and resolve the issue quickly to get the system back to full performance.

The Right Tool for the Job: Fluke GFL-1500 Ground Fault Locator

The fastest and safest way to locate a fault is by using a solar ground fault locator, such as the Fluke GFL-1500 Ground Fault Locator. This tool enables precise fault identification without relying on guesswork, detailed site documentation, or time-consuming manual testing. If you're unfamiliar with this tool, you can read more about the Fluke GFL-1500 Ground Fault Locator here. And once you've found the fault, here's how to repair it safely.

Step-by-Step Guide on How to Locate Hard Ground Faults in Solar PV

Before beginning any troubleshooting, always follow site-specific lockout/tagout (LOTO) procedures and wear appropriate personal protective equipment (PPE). Identifying a fault is just the first step—the ultimate goal is to safely restore system operation.

Step 1: Analyze the System to Detect Ground Faults

The first step is to ensure the DC system is ungrounded and there is no connection between a functionally grounded conductor and the ground. When a ground fault is suspected, confirm its presence and determine which part of the array is affected. Use the Analyze Function of your GFL-1500 to assess system health and identify whether a fault exists.

To run Analyze Function:

1. Enter Setup and input the number of modules in series.
   • This step can also be done after the test is complete by pressing the INFO button and entering the number of modules.
2. Connect the test leads
   • Red to DC positive
   • Black to DC negative
   • Green to the ground (earth or grounded metal)
3. Press the Test button to run Analyze Function.

The tool will measure:

• Open-circuit voltage between positive to negative
• Voltage from positive to ground and negative to ground
• Estimated fault resistance range (if a ground fault is found)

If you've entered the number of modules correctly, the locator will estimate how far into the string the fault may be.

Possible results:

• Hard fault: A low-resistance ground fault is present.
• No fault detected: No voltage to ground found during test.
• High resistance fault: There may be a fault, but not enough current is flowing to trigger the GFDI.
• High capacitance and resistance: System conditions (e.g., long wiring runs) prevent a conclusive result.

Step 2: Determine the Best Side for Tracing the Fault

Next, use the analysis results to determine the best way to inject a tracing signal. You'll choose between sending the signal from the positive or negative side of the array.

Here's how:

• Depending on the workflow, it's often best to choose the side that has the highest voltage to ground. For example, if positive-to-ground is 200 VDC and negative-to-ground is 800 VDC, inject the signal on the negative side.
• Exception: If one side shows 0 VDC to ground, that may indicate a fault in the home run conductor. In this case, it may be easiest to inject the signal on the 0 VDC side to trace from that point.

Step 3: Determine the Signal Mode

The tracing signal can be injected using two different modes, Array and Unit. Array Mode should be used when the voltage of the side selected for tracing (Positive to Ground or Negative to Ground) is greater than 30VDC. Look for the hazardous voltage icon on the Transmitter screen to indicate the voltage is greater than 30VDC. This is the default and recommended mode for tracing. Unit Mode should be used when the voltage of the side selected for tracing is less than 30VDC. For example, in the case of a homerun fault, if the signal is injected on the 0 VDC side. Look for no hazardous voltage icon on the Transmitter screen. Press the MODE button on the Transmitter to toggle between these different modes.

Step 4: Use the Fault Function to Trace the Ground Fault Location

With the fault confirmed, the tracing direction chosen, and the signal mode selected, use the Fault Function to inject a low-current signal. Follow the fault path with the receiver or clamp to find the exact location of the fault.

Tracing process:

1. Inject the fault signal from your chosen side.
2. Identify the faulted branch.
   • The Receiver can be used with disconnections on one side of the circuit (open fuse holders on one set of parallel connections, like on the positive side).
   • The Clamp can be used around branch pairs (positive and negative measured together) without any disconnections.
3. Pinpoint the fault location.
   • The Receiver can be used with disconnections on one side of the circuit. Or you can move the Transmitter to the faulted branch.
4. Use the receiver to follow the signal down the string or the clamp can be used in noisy and higher capacitance environments where there is not a clear path with the trace signal.
   • To clarify the signal when using the clamp, activate the BP filter by pressing the BP button. This is only effective with the Array signal mode on the Transmitter.
   • The Fluke GFL-1500 receiver provides both audio (beeping) and visual feedback (flashing LED indicator) during fault tracing. The beeping/flashing increases in frequency as you get closer to the fault location.

Tips for Accurate Fault Tracing

• Ensure the system is de-energized where required before opening enclosures or accessing conductors.
• Always confirm test leads are connected securely.
• Ensure the DC system is ungrounded and there is no connection between any conductor and the ground.
• If signal tracing becomes unclear, and signal is detected on multiple branches:
  • Double-check which side the signal was injected from
  • Verify that your test string is isolated from parallel branches
  • Try using the Clamp with the BP filter activated. The Transmitter signal must be in Array mode.

What's Next? Locating the fault is just step one. Now that you know where the issue is, it's time to safely perform the repair. Learn how to repair PV ground faults here.

Wrapping Up: Finding the Fault Is Only Half the Fix

Identifying the location of a hard ground fault in a solar PV system is a critical first step in restoring performance and protecting your equipment. By systematically analyzing voltage to ground and tracing the fault path, you can isolate the issue without excessive trial and error.

But remember, locating the fault doesn't resolve it. Once found, it's essential to safely disconnect power, inspect the damaged conductor or component, and repair or replace the faulted part according to site safety procedures and electrical codes.

Ground faults not only reduce energy production they also pose risks to equipment and safety. That's why fast, accurate identification followed by proper repair is key to minimizing downtime and getting back to expected system performance.

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.