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A ground fault on your solar inverter means electrical current is leaking to the grounding system. This is a fire risk that needs prompt attention. Here are 5 solutions that work for Massachusetts solar homeowners.
A ground fault on your solar inverter means current is leaking from the wiring to the grounding system. In Massachusetts, the most common causes are: (1) water infiltration from nor'easters and freeze-thaw cycles entering junction boxes or conduit, (2) squirrel/rodent damage to wire insulation — extremely common in MA, (3) degraded insulation from UV and age on systems 8+ years old, (4) loose connections from thermal cycling (-10F to 100F temperature swings), and (5) damaged conduit from storms or construction. A diagnostic visit costs $150-$300, and most repairs cost $200-$800. Ground faults are a fire hazard — do not repeatedly reset the inverter. Install critter guards ($800-$1,500) to prevent rodent damage, the #1 preventable cause in Massachusetts.
A ground fault occurs when electrical current escapes from its intended path (the wires connecting your solar panels to the inverter) and flows instead to the grounding system — the metal racking, conduit, or equipment chassis. Think of it as a leak in an electrical pipe: current is going somewhere it should not.
Your solar inverter detects this leakage current continuously. When it exceeds a threshold (typically 300 milliamps for residential systems), the inverter shuts down and displays a ground fault error. This is a safety feature — ground faults can cause electrical fires, and the inverter is designed to stop producing power before that happens.
In Massachusetts, ground faults are more common than in drier climates because of our weather: heavy rain, nor'easters, 48 inches of annual snowfall, and over 100 freeze-thaw cycles per year. These conditions stress wiring, connectors, and seals that may have been perfectly fine at installation.
Do NOT repeatedly reset your inverter if a ground fault keeps returning. Each reset re-energizes a faulty circuit, increasing fire risk. If one power cycle does not clear the fault, leave the system off and call a licensed solar electrician. Your panels will still be safe in their de-energized state.
The good news: ground faults are diagnosable and repairable. Most are caused by one of five issues, all of which have established repair procedures. A licensed solar electrician can typically diagnose the problem in a single visit using a megger (insulation resistance tester) and string-by-string isolation.
Your solar system is designed to last 25-30 years. A ground fault does not mean your system is failing — it means one component needs attention. Addressing it promptly protects your home and gets your system back online quickly. Every day your system is down costs you approximately $5-$15 in lost production and SMART program payments.
Massachusetts weather creates unique challenges for solar wiring. Here are the five most common causes, ranked by how often we see them.
Season: Year-round (worst in spring thaw & nor'easters)
Massachusetts receives 48 inches of rain and 48 inches of snow annually. Water can enter junction boxes, conduit fittings, and wire terminations through degraded seals. Freeze-thaw cycles (over 100 per year in eastern MA) cause thermal expansion that loosens fittings over time.
Prevention: Ensure all conduit fittings use liquid-tight connectors. Request a sealant inspection during annual maintenance.
Season: Year-round (peak: fall nesting)
Eastern gray squirrels are abundant throughout Massachusetts. They chew through wire insulation to sharpen their teeth and nest under solar panels for warmth. A single chew-through can expose copper and create a ground fault. Some homeowners experience repeated damage.
Prevention: Install galvanized critter guards around the panel perimeter ($800-$1,500). This is the #1 recommended preventive measure in MA.
Season: Gradual — appears after years of exposure
Wire insulation degrades over time from UV radiation, temperature cycling, and ozone exposure. Systems installed before 2016 may use older insulation compounds that degrade faster. PV wire rated for outdoor UV exposure lasts 25+ years, but cheaper non-PV-rated wire can fail in 8-12 years.
Prevention: Ensure all exposed wiring is PV-rated (USE-2 or PV Wire). Request an insulation resistance test during annual inspections after year 8.
Season: Worst after extreme temperature swings
Massachusetts experiences temperature swings of 100+ degrees F annually (-10F to 100F). Metal connectors expand and contract, which can loosen wire terminations over time. A loose connection can arc and create a ground fault. MC4 connectors are especially susceptible if not properly torqued at installation.
Prevention: Request a torque check on all accessible connections during annual maintenance. Thermal imaging can detect hot spots from loose connections.
Season: After storms, ice, or construction activity
Conduit protects wiring from physical damage. Falling branches, ice buildup, ladder impacts, or roofing work can crack or crush conduit, exposing the wires inside to moisture and physical contact with grounded metal. This is especially common after nor'easters or when roofers work near solar equipment.
Prevention: Use schedule 40 PVC or metallic conduit in exposed areas. Brief your roofer on solar equipment locations before any roof work.
Our licensed electricians specialize in solar system diagnostics. Same-day appointments available in the Greater Boston area.
Follow these steps in order. Steps 1-2 are safe for homeowners. Steps 3-5 require a licensed solar electrician.
From the ground level, visually inspect all visible wiring, conduit, and connections running from your panels to the inverter. Look for chewed insulation (rodent damage), cracked conduit, exposed copper wire, or discolored/melted connectors.
If the ground fault appears during or after rain, moisture infiltration is the likely cause. Junction boxes on the roof, combiner boxes, and the area where conduit enters the inverter are all potential water entry points.
Do NOT open any electrical boxes yourself. Only a licensed electrician should open junction boxes, combiner boxes, or the inverter.
A megger test (insulation resistance test) measures the integrity of wire insulation by applying a high voltage and measuring leakage current. This is the definitive test for locating a ground fault. It requires specialized equipment and a licensed electrician.
This test involves high voltage and must ONLY be performed by a licensed electrician. Never attempt this yourself.
For systems with multiple strings, a technician can disconnect strings one at a time and attempt to restart the inverter after each disconnection. When the ground fault clears, the last disconnected string contains the fault.
String isolation involves working with live DC voltage from solar panels. This is extremely dangerous and must be performed by a qualified solar technician.
If Steps 1-2 do not reveal an obvious visible cause, or if the fault persists after a power cycle, call a licensed solar electrician. Ground faults are not a DIY repair. Have your system details ready when you call.
| Service | Cost Range |
|---|---|
| Diagnostic visit (megger test + inspection) | $150-$300 |
| Connector replacement (MC4) | $100-$250 |
| Junction box repair/reseal | $150-$350 |
| Wire/cable run replacement | $200-$500 |
| Extensive rodent damage repair | $500-$800 |
| Critter guard installation | $800-$1,500 |
| Conduit repair/replacement | $200-$600 |
Costs reflect Greater Boston area rates as of April 2026. Rural western MA may be $50-$100 lower. Same-day emergency service typically adds $50-$100 premium.
If your ground fault was caused by rodent damage, installing critter guards should be part of the repair. Critter guards are galvanized mesh clips that attach to the panel frame and close the gap between the panels and the roof. They prevent squirrels, chipmunks, birds, and other animals from accessing the wiring underneath.
Massachusetts has one of the densest eastern gray squirrel populations in the country. We see rodent-caused ground faults on roughly 1 in 5 service calls. Without critter guards, the same damage will likely recur within 6-18 months.
NuWatt recommends critter guards for every solar installation in Massachusetts. If your system was installed without them, adding them during a ground fault repair visit is the most cost-effective time — the electrician is already on-site. Learn more about our critter guard options in our solar critter guard and pest protection guide.
Not sure if your ground fault is a DIY fix or needs professional help? Our solar technicians provide free phone consultations and can schedule a diagnostic visit within 48 hours.
Ground faults involve electrical current flowing where it should not — which means fire risk. Here is a clear line between what you can safely check yourself and what requires a professional.
When you call, have the following ready: your system size (kW), inverter brand and model, the specific error code displayed, when the fault first appeared, and whether it correlates with weather. This information helps the technician prepare the right parts and tools for a first-visit repair. For more information about maintaining your solar system, see our solar panel warranty guide and solar production monitoring and troubleshooting guide.
Nor'easters bring a unique combination of heavy rain (2-4 inches), high winds (40-70 mph), and temperature drops that create specific ground fault patterns. Understanding these patterns helps you determine whether your ground fault is weather-related or a persistent wiring issue.
Freeze-thaw cycles crack seals. Snowmelt enters conduit fittings. Peak season for ground faults from moisture.
Thunderstorms drive rain sideways into normally protected areas. UV degradation accelerates. Rodent activity peaks.
Squirrels nest under panels for winter. Leaf debris traps moisture against conduit. Nor'easter season begins.
Ice dams push water under flashings. Snow load stresses connections. Temperature at lowest — wire contracts most.
If your ground fault appeared during or within 24 hours of a storm, give it 48 hours to dry out before scheduling a repair. Many weather-related ground faults self-resolve as moisture evaporates. If the fault persists after 48 hours of dry weather, the water has found a path into the wiring that will recur with the next storm.
For information about how Massachusetts weather affects solar production more broadly, see our solar panels and Massachusetts weather guide.
Complete monitoring guide with benchmarks and alert diagnosis
Prevent rodent damage with critter guards
Understand what's covered under your warranty
How weather affects your system performance
A ground fault means electrical current is leaking from the intended circuit path to the grounding system. In solar panels, this typically indicates damaged wire insulation, moisture in a junction box, or a compromised connection. Ground faults are a fire hazard and should be investigated promptly. Your inverter shuts down as a safety measure when it detects this condition.
Our licensed electricians diagnose and repair solar system faults same-day in the Greater Boston area. We carry megger testers, replacement connectors, and critter guard materials on every truck.