In July 2026, a fire broke out at a hospital in North Yorkshire, UK. According to Euronews, the solar PV system was identified as one of the possible causes, although the full investigation report has not yet been released.

At this stage, it would therefore be inaccurate to conclude that the fire was caused by the PV modules, cables, or any other specific component. However, the incident is a timely reminder that as rooftop solar systems become increasingly common on hospitals, schools, residential buildings, and commercial and industrial facilities, fire safety must receive greater attention.

Fire Risk Must Be Considered Across the Entire PV System

A solar PV system consists of modules, connectors, cables, inverters, and other electrical equipment.

Loose connections, improper installation, damaged cables, ageing components, or prolonged overloading may all increase the risk of localised overheating and electrical faults.

Cables are not the only potential source of fire risk in a PV system. However, they are often installed in groups along mounting structures, cable trays, or rooftops. If a fire occurs nearby, the ability of the cable to limit further flame spread may directly affect the extent of the fire.

The purpose of flame-retardant testing is therefore not to prove that a cable “cannot burn.” Instead, it is used to verify whether the cable can restrict flame propagation after being exposed to an external flame.

Single Vertical Flame Test

The single vertical flame test is used to observe the behaviour of one vertically mounted cable when it is exposed to a specified flame.

During the test, a flame is applied to the cable for a specified period. After the flame source is removed, the cable is observed to determine whether it continues to burn and whether the flame spreads upward along the cable.

The test images and results show that:

After the flame source was removed, the flame did not continue to spread upward along the cable, and no sustained flame propagation was observed.

This indicates that the cable was able to restrict flame spread under the specified test conditions.

Vertical Flame Spread Test for Bunched Cables

In real-world installations, cables are rarely used individually. Multiple cables are often installed together.

When cables are grouped, the total volume of insulation and sheath materials increases. Heat can also accumulate more easily, resulting in a greater risk of flame spread than with a single cable.

For this reason, a flame spread test for bunched cables is also required.

During the test, multiple cables are mounted on a standard vertical ladder and exposed to a flame under specified conditions.

The test results show that:

After the flame source was removed, the flame did not continue to spread upward, and no significant sustained flame propagation was observed across the cable bundle.

This test more closely reflects cable installations found on commercial and industrial rooftops, in solar power plants, and on cable trays. It provides a more practical indication of how effectively the cables can restrict flame spread when installed together.

Flame-Retardant Testing Is One Part of PV System Safety

The safety of a PV system cannot be ensured through a single test alone.

In addition to flame-retardant performance, project owners and installers should also consider:

• Whether the cable cross-sectional area and current-carrying capacity are suitable;

• Whether the connectors are fully compatible;

• Whether crimping and installation have been carried out correctly;

• Whether the cables show any signs of damage or ageing;

• Whether the system is inspected and maintained regularly.

At the KUKA Cable laboratory, single vertical flame tests and vertical flame spread tests for bunched cables are carried out to evaluate cable behaviour under specified fire conditions.

These tests cannot guarantee that a PV system will never experience a fire. However, they allow customers to assess the flame-retardant performance of the cables more clearly and provide useful evidence for product selection and project safety.

As solar PV systems are increasingly installed on building rooftops, safety should not exist only as a claim in a product brochure. It should be demonstrated through real testing and clearly defined standards.