When designing or selecting components for photovoltaic (PV) systems, choosing the right DC solar cable is about more than just voltage rating and conductor size. The true long-term performance of a cable depends heavily on the thermal stability and structural integrity of its insulation and sheath materials. One of the most critical indicators of this is thermal elongation performance.
What Is the Thermal Elongation Test and Why Is It Important
The thermal elongation test, defined by international standards such as IEC 60811-507 and EN 50618, is designed to evaluate the heat resistance and mechanical stability of polymeric materials used in cable insulation and sheaths. The test simulates extreme temperature and mechanical stress conditions to determine whether the material can retain its shape and function over time.
Understanding Thermal Elongation in Simple Terms
A photovoltaic cable can be compared to a soldier marching across a desert. Exposed to high ambient temperatures, continuous current, and solar radiation, the outer sheath must remain structurally sound. If the material softens, stretches, or cracks, the cable could eventually fail in real-world applications. The thermal elongation test replicates these harsh conditions in a controlled environment to assess the cable's durability.
How Thermal Elongation Testing Works
At KUKA, we use stringent testing procedures to ensure realistic and consistent evaluation. Each sample is subjected to the following conditions:
Test Temperature: 250 degrees Celsius
Tensile Load: 20 Newtons per square centimeter
Load Duration: 15 minutes
Unload Observation Period: 5 minutes
Samples Tested: Three sections from both the insulation and sheath
Pass-Fail Criteria Based on Industry Standards
To qualify as a thermally stable, properly crosslinked material, a cable must meet both of the following criteria:
| Test Indicator | Maximum Allowable Value |
|---|---|
| Elongation under load | 100 percent |
| Permanent deformation after unloading | 25 percent |
Comparative Thermal Elongation Test Results
We conducted tests on KUKA CABLE alongside several other commercially available PV cable brands. All tests followed the same conditions described above. The table below summarizes the results:
| Brand | Breakage Occurred | Time of Break (min) | Elongation Under Load | Permanent Deformation | Meets TÜV Standard | Notes |
|---|---|---|---|---|---|---|
| KUKA CABLE | No | ≥15 | 83 percent | 13 percent | Yes | Stable performance, high crosslinking quality |
| Brand A | Yes | 4 | Not measurable | Not measurable | No | Failed early, test incomplete |
| Brand B | No | ≥15 | 145 percent | 32 percent | No | Material softened significantly under heat |
| Brand C | Yes | 6 | Not measurable | Not measurable | No | Failed before reaching minimum test time |
Why Thermal Elongation Performance Matters
1. It Reveals the Quality of Crosslinking Technology
A cable labeled as "crosslinked" may not always meet thermal performance expectations. The thermal elongation test uncovers the true effectiveness of the crosslinking process by showing whether the material remains stable under extreme conditions.
2. It Directly Impacts Safety and Lifespan
Thermal deformation can lead to surface cracks, allowing moisture ingress, which can result in insulation failure, short circuits, or even fire. Ensuring a cable passes thermal elongation testing helps prevent these safety hazards from occurring.
3. It Reduces Maintenance and Replacement Costs
Cables that fail thermal elongation testing are more likely to degrade or fail within just a few years. In contrast, KUKA CABLE and similar high-performance products can last 20 to 25 years or more. This significantly reduces long-term costs and improves return on investment.
Final Thoughts: Not All Cables Are Created Equal
Many cables may appear compliant based on surface-level specifications, but real-world testing often reveals hidden weaknesses. Premature breakage, poor crosslinking, and excessive elongation are common among low-quality products.
Solar Cables that pass all aspects of the thermal elongation test are built with better materials, stronger processes, and more reliable quality control. While they may not always be the lowest-cost option, they often prove to be the most reliable and safest investment in photovoltaic infrastructure.
