Introduction: A Growing Concern
The global solar photovoltaic industry is expanding at an unprecedented pace. As of mid-2026, the United Kingdom alone has over two million solar PV installations in operation. Yet with this rapid growth comes a hidden risk that every system owner, installer, and facility manager must take seriously: fire.
A recent survey by global industrial insurer QBE has identified a sharp rise in fires linked to photovoltaic systems. According to the company's analysis, the number of solar-related fires increased by 133% between 2022 and 2025 -more than double the 52% growth rate of new installations during the same period. In 2025 alone, UK fire services recorded 212 fires involving solar panels.
Perhaps the most striking finding of the QBE survey is this: DC cabling and plug connections are the most common cause of PV fires. Of the 212 recorded fires in 2025, 49 were directly attributed to issues with DC cabling and connectors. This far exceeded fires caused by solar modules (36 cases), battery storage systems (23 cases), and inverters (19 cases).
As Tobias Mehl, Risk Manager at QBE Germany, noted: "Our experience shows that the cause often lies not in the solar modules themselves, but in faulty cable connections, connectors, or other electrical components."
This article aims to help you understand why DC cabling and connectors pose such a significant fire risk-and, more importantly, how you can protect your solar assets.
Why DC Cabling and Connectors Are the Weakest Link
To understand the risk, we must first understand the nature of direct current electricity.
Unlike alternating current (AC), which periodically drops to zero current (the "zero-crossing" point) and can self-extinguish an arc, DC current flows continuously in one direction. This means that when an electrical arc forms in a DC circuit, it has no natural way to extinguish itself. The arc can persist indefinitely, generating localized temperatures as high as 3,000°C to 6,500°C -hot enough to melt copper conductors and ignite surrounding materials.
In a PV system, DC cabling and connectors are the arteries through which high-voltage DC power flows from the solar modules to the inverter. A typical 1MW rooftop solar installation may contain as many as 2,000 connection points. Each of these points represents a potential failure site.
The three primary mechanisms that lead to DC connector and cabling fires are:
Poor Connections and Loose Fittings - When connectors are not fully inserted, improperly crimped, or insufficiently tightened, contact resistance increases. This resistance generates heat through the I²R effect. Over time, thermal cycling (daytime heating and nighttime cooling) causes connections to loosen further, escalating resistance and heat until the connector fails catastrophically.
Incompatible Connectors - Mixing connectors from different manufacturers is a common but dangerous practice. Even when manufacturers claim compatibility, dimensional tolerances can vary, leading to incomplete mating, poor sealing, and eventual failure.
Cable Damage and Insulation Breakdown - DC cables can be damaged during installation by sharp roof edges or metal trays. Over time, UV exposure, temperature extremes, and physical stress degrade insulation. When the conductive core is exposed to moisture or comes into contact with earthed structures, parallel arcing can occur-a fault that is ten times more destructive than series arcing.
The consequences of a DC arc fault can be devastating. Beyond the immediate fire damage, an incident can lead to extended business interruption, loss of revenue, increased insurance premiums, and reputational harm. Critically, QBE's research also shows that fires are increasingly spreading beyond the solar array to the wider building-from 33 such cases in 2022 to 88 in 2025.
Practical Steps to Reduce Your Fire Risk
The good news is that DC cabling and connector fires are largely preventable. By implementing the following measures, you can significantly reduce the risk to your solar installation.
1. Choose Quality Components from the Start
Use certified components only. Ensure all connectors carry TUV or UL certification. Counterfeit or substandard connectors are a leading cause of failures in many markets.
Specify solar-grade DC cables. Use PV1-F rated cables designed for UV resistance, high temperatures (up to 120°C), and double insulation. Standard PVC cables degrade rapidly in rooftop conditions.
Never mix connector brands. Both ends of every DC connection should come from the same manufacturer. If you must replace a connector, replace the entire pair with matching components.
Consider connectors with proven reliability. Products like the original MC4 connector, featuring MULTILAM technology, are designed to maintain low contact resistance over the entire system lifetime.
2. Ensure Professional Installation
Use the correct tools. Connector crimping must be performed with the manufacturer's specified crimping tool. Improper crimping is one of the most common causes of premature connector failure. A ratcheting crimp tool delivering 1,500–2,000 lbs of force with hexagonal dies is recommended.
Follow torque specifications. MC4 connectors should be tightened to the specified torque (typically 3–5 turns), and inverter DC terminals should meet the specified torque values.
Protect cables during installation. Route cables away from sharp edges and use conduits or trunking where cables pass through metal structures. Ensure cable bending radii meet the minimum requirement (at least five times the cable diameter).
Provide adequate ventilation. Maintain sufficient clearance between panels and the roof surface to allow heat dissipation.
3. Implement a Rigorous Inspection and Maintenance Program
The risk of fire increases with system age. Older installations are significantly more likely to experience failures due to degraded components and outdated maintenance practices.
Conduct thermal imaging inspections every 6 to 12 months. Infrared thermography can detect hot spots at connection points before they escalate into failures.
Perform annual DC cable insulation resistance testing. The insulation resistance should exceed 1 MΩ.
Check every MC4 connector for tightness at least once a year.
Inspect cables for physical damage. Look for signs of abrasion, cracking, UV degradation, or animal gnawing.
Examine junction boxes and terminals for signs of overheating, oxidation, or burning.
4. Consider Advanced Safety Technology
Install Arc Fault Circuit Interrupters (AFCI). These devices can detect the unique signature of a DC arc and disconnect the circuit before a fire can develop.
Consider rapid shutdown devices. These systems can reduce DC string voltage to below 30V within 30 seconds, protecting firefighters and reducing arc risk.
Evaluate passive safety solutions. Products like the ArcBox enclosure snap around DC connectors to contain any arc that does occur, preventing it from spreading to surrounding combustible materials.
Implement terminal over-temperature detection. Real-time monitoring of connection point temperatures can identify developing faults-such as poor contact, loose connections, or oxidation-before they become critical.
Conclusion: Safety Is an Investment, Not a Cost
One thing we can learn from the QBE report is that the rise of solar energy means we must invest more in safety. Even though the average fire risk per installation remains low (around 0.07 incidents per 1,000 systems in the UK), the increasing trend in the number of accidents should make us even more cautious.
Fires from DC wiring and connectors, and their causes can all be avoided. The possible cause of such accidents lies in defective components, quality of solar system installations, and lack of maintenance.
Using only certified components, hiring professionals for installation, regularly inspecting the solar systems, and applying new technologies are ways to keep your investment, staff and facility safe.
