On a dry August afternoon in Cupertino, a small arc hidden under a solar rail can smolder for hours before anyone sees smoke on the roof. From the street, the array looks perfectly normal, and the monitoring app might still show healthy production. The problem is buried in a connection that was never grounded and bonded quite the way the National Electrical Code intended.
If you own a home or commercial building in the Bay Area, you have probably heard stories about solar-related roof fires and wondered how real that risk is. Many people assume the danger comes from bad panels or inverters, and that a passed inspection means everything on the roof is electrically safe. In reality, the bigger fire risks often come from invisible grounding and bonding mistakes that let stray DC current flow through mounting rails and roof structure instead of clearing through a safe path.
At Cobalt Power Systems Inc, we have designed and installed more than 3,500 photovoltaic systems across the San Francisco Bay Area since 2003, and we are regularly called in to evaluate or fix systems installed by others. Grounding and bonding issues are among the most common and most serious problems we find, including on arrays that passed their original inspections. In this article, we want to unpack how those errors actually create fire risk, why they are so easy to overlook, and what you can do to make sure your system is built differently.
For safe and reliable solar services, let Cobalt Power Systems Inc., a San Francisco Bay Area Solar System Designer from our team help you install quality solar panels for your home! Call (650) 817-7791 or contact online today.
Why Grounding Errors Matter More Than Most People Think
Most solar owners hear the word “ground” and picture a single green wire tied into the electrical panel or a rod driven into the dirt. In a photovoltaic system, grounding and bonding involve much more. Grounding connects the electrical system to the earth so fault current has somewhere to go. Bonding ties all of the conductive metal parts together so they stay at the same electrical potential and do not surprise you by becoming energized when something goes wrong.
On a rooftop array, that means every rail, module frame, junction box, and conduit fitting should be part of one continuous bonded network, which in turn is connected to the building’s grounding system. When there is a fault, such as a conductor nicked on the rail or a connector that has worked loose, that bonded network provides a low-resistance path back to the source. This allows breakers or fuses to trip quickly and shut down the fault before it can generate dangerous heat.
DC solar circuits behave differently from the AC circuits that power your appliances. Once a DC arc starts, it can sustain itself more stubbornly, because there is no natural zero-crossing of the waveform to help extinguish it. If grounding is incomplete and the fault path is high resistance, current finds strange ways through rails and roof hardware and can sit there heating a small area of wood or underlayment for a long time. That is why seemingly small grounding mistakes, such as a missing bonding washer or a loose lug, matter so much.
Because city and utility inspections are designed to verify basic code compliance, many owners assume that a green sticker means every bond and ground is perfect. In practice, inspectors are working against tight schedules and may not have access to check each hidden connection on a roof. As a Maxeon Preferred Partner, Tesla Premier Certified Installer, and SunPower Dealer of the Year, we have seen in the field that simply meeting a checklist is not enough. Grounding has to be treated as a system-level design and installation priority, not just a box to tick.
How Stray DC Current Turns Mounting Rails Into Ignition Sources
To understand how a grounding error can turn an aluminum rail into an ignition source, it helps to walk through a simple fault scenario. Imagine a string of DC wiring running along a rail under your modules. Years after installation, a clamp is over-tightened during maintenance or a bit of thermal movement causes the insulation to rub through on a sharp edge. The conductor makes intermittent contact with the rail, energizing that metal whenever the array is producing.
If the rail and all attached metal parts are properly bonded, and that bonded network is solidly connected to the building’s grounding system, the moment the conductor faults to the rail, a large fault current flows through that low-impedance path. That current quickly rises high enough to trip a breaker or blow a fuse, which removes power from the faulted circuit. You might see an error on your inverter or a trip at the service panel, but the fault is cleared before anything on the roof gets dangerously hot.
Now consider the same fault on a rail section that is not actually bonded to the rest of the system because a bonding jumper was omitted, or a bonding washer was installed over paint or anodizing that prevents good electrical contact. That rail can sit “floating” at several hundred volts relative to the building and earth. When current tries to return through high-resistance, makeshift paths, it can create small, sustained arcs at loose fasteners, corroded joints, or tiny gaps between components.
Those arcs concentrate heat in very small spots. On a typical Cupertino or South Bay roof, that spot might be a screw passing through a combustible deck, dry underlayment, or a piece of resin-based flashing. In a region with long dry summers and wood-framed roofs, it does not take a large flame to start a slow-burning fire that spreads into attic spaces. The array can look intact from the street while the problem develops underneath.
At Cobalt Power Systems Inc, our in-house CAD and electrical design teams model grounding and bonding paths as part of the layout process, not as an afterthought in the field. We choose rail layouts, bonding hardware, and conductor routes so that every module frame and rail segment is intentionally part of a bonded network that can carry fault current reliably. That design work, combined with disciplined installation, reduces the chance of isolated rail sections that let stray DC current create ignition points.
Common Solar Grounding Errors We See On Bay Area Roofs
Once you start looking closely at rooftop arrays, patterns emerge. Certain grounding and bonding mistakes show up again and again on systems we are asked to inspect or repair in the South Bay, Peninsula, and along the coast. Many of these arrays have been operating for years without obvious issues, which is part of what makes the risk deceptive.
One of the most frequent problems is missing or ineffective bonding between rail sections. Installers may assume that a mechanical splice or shared mounting bracket automatically bonds two rails together. In reality, the presence of anodizing, paint, or dirt can block electrical continuity. If a bonding jumper or bonding splice plate is not used where the manufacturer requires it, you can end up with a long run of metal that is connected structurally but floating electrically.
We also see rail bonds and lugs installed over painted surfaces or heavy anodizing without proper preparation. Metal that looks tightly clamped can still have a thin insulating layer that raises resistance. Over time, thermal cycling and corrosion can worsen the contact, creating high-resistance points that heat up under fault current or prevent overcurrent devices from tripping when they should.
Another recurring issue is unbonded module frames. Many module mounting systems rely on specific hardware, sometimes called WEEBs or integrated bonding clips, that bite through frame coatings and rail finishes to create a conductive path. When installers mix and match hardware, reuse components, or miss a clip, individual modules or entire rows can be electrically isolated. During a ground fault, those frames can sit at dangerous voltage relative to the rest of the array and to the roof structure.
Age and roof work add another layer of risk. Coastal air and fog can introduce corrosion on lugs and bonding jumpers, especially if incorrect materials were used. Reroofing, HVAC replacements, and satellite dish installations often involve removing and reinstalling sections of racking. It is common to find rails put back without the original bonding hardware, or jumpers left disconnected after flashing work. Because all of this happens out of sight, owners have no reason to suspect that their grounding network is no longer intact.
Our installation teams at Cobalt Power Systems Inc, supported by a fleet of 32 trucks and in-house logistics, follow standardized practices that specifically address these weaknesses. We use manufacturer-approved bonding hardware, prepare contact surfaces correctly, verify continuity where required, and document the grounding approach so future maintenance has a clear reference. That consistency is difficult to achieve with ad hoc crews or one-off subcontractors, and it is one of the reasons we often find fewer grounding issues on systems we installed ourselves.
Why Passing Inspection Does Not Guarantee Safe Grounding
Homeowners and building managers often tell us that the city inspector signed off, so the system must be safe. It is understandable to view that green tag from Cupertino or another Bay Area jurisdiction as a complete bill of health. The reality is that inspections are an important safeguard, but they are not exhaustive exams of every connection on your roof.
During a typical PV inspection, the authority having jurisdiction checks key items like conductor sizing, overcurrent protection, disconnect locations, labeling, and visible grounding conductors and lugs. On the roof, an inspector may look at a sample of module clamps and bonding hardware, pull on a few wires, and verify that at least one rail bond ties into the equipment grounding conductor. Given the time pressures inspectors work under, they simply cannot loosen every module, test every splice, or confirm continuity across every rail segment.
What often goes unverified are the subtle parts of the grounding and bonding network that cause most of the trouble. An inspector is unlikely to scrape under each lug to see if it was installed over paint, or to continuity-test every mid-rail to confirm that bonding clips were used consistently. They also generally do not perform ground resistance testing on the building’s grounding electrode system as part of a PV inspection, even though that system is a critical part of how faults clear.
This means an array can meet the letter of the NEC as visible from accessible points and still have hidden weaknesses. If those weaknesses never see a fault, the system may appear fine for years. When a conductor eventually chafes or a connector fails, there may not be a reliable path for fault current to return to the source and trip a breaker. The fault energy is then dissipated in the form of heat and arcing at whatever high-resistance paths are available, often at the roof itself.
Because Cobalt Power Systems Inc handles permitting and utility coordination across many Bay Area cities, we are very familiar with how inspections proceed in the field. We view the inspection as a minimum bar, not the finish line. Our internal commissioning process goes beyond what an inspector can practically check, with specific grounding and bonding verifications built into our installation and first-year complimentary system checkups.
Soil Resistance & Ground Electrodes: The Hidden Part Of Fire Risk
Even if every rail, module frame, and junction box is bonded perfectly, the path from that bonded network into the earth itself matters. This is where the grounding electrode system and soil resistance come into play. The grounding electrode system might include ground rods, concrete-encased rebar sometimes called a Ufer ground, or building steel tied into the service equipment.
When a fault occurs, current flows not just through copper wire, but also through the soil around your grounding electrodes. If that soil has relatively low resistance, it forms part of a low-impedance path that allows a significant spike in fault current, which helps overcurrent devices trip quickly. If the soil has high resistance, the ground electrode system can behave like a bottleneck, limiting fault current and keeping it from ever reaching the levels required to operate protective devices properly.
The Bay Area has a mix of soil conditions, from coastal areas with higher moisture to inland neighborhoods with rocky or compacted soils that may have higher resistance. Building codes address grounding electrode installation, but they do not automatically guarantee a specific resistance value at every site. Over time, corrosion, changes in moisture, or disturbed soil from construction can change how well your electrodes perform.
For a solar owner, the practical takeaway is that having a ground rod is not the same as having an effective ground path. In some cases, additional electrodes, bonding to existing concrete-encased electrodes, or other measures may be needed for a robust grounding electrode system. This is especially relevant when a PV system is combined with storage, EV charging, or service upgrades that increase available fault current and the importance of a reliable path to earth.
Because Cobalt Power Systems Inc manages not just PV installations, but also electrical upgrades and energy storage integrations, we have the in-house capability to evaluate how the solar grounding ties into the existing building grounding electrode system. When a project or service call indicates that grounding performance may be marginal, we can work with the property’s electrical infrastructure to improve that connection, rather than treating the array as a standalone system.
How Grounding Errors Happen During Design, Installation & Maintenance
Grounding and bonding problems rarely come from a single dramatic mistake. They usually appear as a series of small decisions or oversights across the life of a system, starting at the design desk and continuing through installation and years of maintenance. Understanding where those decisions occur can help you ask better questions and choose contractors who treat grounding as part of the core design, not a leftover detail.
In the design phase, choices about rail layout, row spacing, and conductor routing set the stage for how easy or hard it will be to create a continuous bonded network. If a designer does not think about where bonds and jumpers will go, installers may find themselves improvising in the field, creating unnecessary breaks or complicated bond paths. The tie-in point to the building’s main grounding system also matters. A poorly chosen connection point can create long, convoluted fault paths instead of direct, low-impedance routes.
Installation shortcuts are another major source of grounding errors. When project schedules are tight, it can be tempting for crews to skip a bonding jumper or rely on rail splices that were never intended to carry fault current. Lugs may be installed without cleaning contact surfaces, or hardware may be under-torqued or over-torqued, both of which can cause long-term reliability issues. None of these shortcuts are visible from the ground, and a quick roof inspection may not reveal them either.
Maintenance and other trades bring their own risks. A roofer may remove rails for a re-roof and then reinstall them without the original bonding clips. An HVAC contractor might run conduits or supports through array areas, disturbing existing bonds. Satellite dish installers may drill into rails or frames without any awareness of how that affects grounding. Each small disturbance can break continuity, leaving sections of the array no longer solidly bonded.
At Cobalt Power Systems Inc, our 10,000 square foot facility in Mountain View houses CAD design, logistics, and support teams that work closely with our installation crews. We produce detailed layouts and hardware schedules that show how grounding and bonding will be executed, so technicians are not guessing on site. Because we offer long-term services like panel cleanings, system checkups, and electrical upgrades, we also have a structured way to revisit and verify grounding as systems age or as other work is done on the building.
What Bay Area Property Owners Can Do To Reduce Grounding-Related Fire Risk
For most homeowners and property managers, opening junction boxes or testing ground resistance is not realistic or safe. That does not mean you are powerless. There are straightforward questions and observations that can tell you a lot about how seriously a contractor treats grounding and bonding, whether you are planning a new system or evaluating one that is already on your roof.
When you talk with an installer about a new project, ask how they design and document their grounding and bonding plan. Ask if they use manufacturer-specified bonding hardware between rails and module frames, and if they can explain how each row and section is tied into the building's grounding system. It also helps to ask what tests they perform at commissioning to verify continuity of equipment grounds and, when appropriate, the performance of the grounding electrode system.
If you already have solar, it may be worth a professional evaluation if the system is older, has been through a reroof or major roof work, has visible corrosion on mounting hardware, or shows intermittent electrical behavior like unexplained inverter trips. You can visually note whether rails appear to have bonding jumpers across breaks or roof transitions, and whether ground lugs look clean and intact, but any detailed testing or repairs should be handled by a trained electrician or solar technician.
As part of our customer-focused approach at Cobalt Power Systems Inc, we offer free consultations for new projects and a complimentary system checkup after the first year of operation for residential systems. Those visits are natural opportunities to confirm that grounding and bonding are still performing the way they were designed, and to identify any concerns early. For systems we did not install, we can perform a focused safety and performance review that includes a close look at grounding, then provide a clear plan for any corrective work if needed.
Why Grounding-Focused Design Matters Even More With Storage & EV Charging
Many Bay Area homes and businesses are adding batteries, EV chargers, and upgraded service equipment to work alongside their solar arrays. These additions bring real benefits, but they also create more complex electrical systems with additional grounding and bonding points. When these systems are designed in isolation, fault currents can take unexpected paths and increase the consequences of any existing grounding error in the PV array.
Energy storage systems tie DC batteries, inverters, and control electronics into your home’s electrical system. EV chargers introduce high-current circuits and, in some cases, their own ground-fault protection schemes. If the grounding and bonding strategy for these systems is not coordinated with the solar array and the main service equipment, a fault in one system can cause confusing symptoms in another, or fail to clear the way protective devices are intended to work.
This is particularly important when available fault current increases because of new equipment or service upgrades. A grounding path that was marginal before may no longer be acceptable when more energy is available to feed a fault. Conversely, if grounding is inconsistent, a protective device might not see enough current to trip even as dangerous heating and arcing occur along unintended paths.
Because Cobalt Power Systems Inc works on grid-tied PV systems, energy storage integrations, EV chargers, and electrical upgrades, we approach grounding as a property-wide design problem rather than a panel-by-panel detail. That perspective helps us create systems where solar, storage, and charging work together with a coherent grounding and bonding plan that supports both performance and protection over the long term.
Protect Your Roof By Treating Grounding As Part Of The Design, Not An Afterthought
Solar has helped many Bay Area owners cut utility bills and gain more control over their energy, but the long-term safety of any system rests on details most people never see. Grounding and bonding live under rails, behind junction boxes, and inside service equipment, quietly ready to carry fault current when something goes wrong. When those details are incomplete, the same rails that support your modules can become hidden ignition sources, especially on dry Cupertino roofs in late summer.
The good news is that grounding is not a mystery. With thoughtful design, disciplined installation, and periodic verification, it is possible to build PV systems that route faults safely back to the source instead of into your roof structure.
If you are planning a new system or have questions about one already on your property, our team at Cobalt Power Systems Inc can review your goals, your electrical infrastructure, and your array layout with grounding and bonding front and center. To discuss your project or schedule a safety-focused evaluation, call us and speak with our team at (650) 817-7791