Photovoltaic (PV) module termination strength testing verifies the mechanical robustness of a module's electrical lead-out system, including the junction box, output cables, connectors, and terminal blocks, under tensile, bending, compressive, and torsional loads. Conducted in accordance with IEC 61215-2 (test MQT 14) and IEC 61730-2 (test MST 22), this evaluation is a mandatory element of design qualification and safety certification for solar modules expected to deliver more than 25 years of field service.
Technical Overview
Termination strength testing, often referred to as lead-out or output terminal robustness testing, examines every electrical interface through which a photovoltaic module delivers power to the external circuit. These interfaces include junction boxes, output cables and their connectors, flying leads, screw-type terminal blocks, and any internal busbar-to-box connections. Because terminations are among the most mechanically stressed parts of an installed module, qualification standards require proof that they can withstand the forces of transportation, installation, cable routing, wind-induced vibration, thermal expansion and contraction, and accidental pulling over the entire service life.
The principal governing documents are the IEC 61215-2 design qualification standard (sequence test MQT 14, robustness of terminations, which invokes the detailed procedures of IEC 60068-2-21, environmental testing, Test U) and the IEC 61730-2 safety qualification standard (test MST 22, strain relief). In North America, UL 61730 and its predecessor UL 1703 impose comparable requirements, while the Chinese national standards GB/T 9535 and GB/T 20047 are aligned with the corresponding IEC publications. Typical failure modes detected by this testing include conductor breakage, insulation tearing, slippage of the cable through the strain relief, potting or adhesive cracking, junction box detachment, and loosening of screw terminals, any of which can ultimately produce arcing, hot spots, or fire in the field.
Testing Samples
Complete Crystalline Silicon and Thin-Film Modules
For full design qualification, tests are performed on complete modules representative of standard production, using the sample quantities defined in the IEC 61215-2 test plan. The module must be fitted with its intended junction box, cables, and connectors exactly as shipped, because any substitute hardware invalidates the result.
Bifacial and Double-Glass Modules
Glass-glass constructions, frameless laminates, and bifacial products are tested in their actual mounting configuration, since the absence of a conventional frame changes how installation loads are transferred to the terminations.
Component-Level Specimens
Junction box manufacturers, cable suppliers, and module makers frequently evaluate components in isolation, including junction boxes mounted on representative laminate sections, cable and snap-lock connector assemblies, and potting compounds. Component-level testing supports incoming inspection, supplier qualification, and rapid design iteration.
Special Termination Configurations
Modules with screw-terminal junction boxes, integrated bypass electronics, detachable lead systems, or rear-mounted terminations require tailored fixtures so that loads are applied along the anatomical axes defined for each termination type.
Testing Items
- Axial tensile (pull) strength of output cables, cords, and flying leads
- Axial compressive (push) resistance of terminals and pins
- Bending endurance of leads and terminations under repeated flexural loading
- Torque strength of screw-type terminals and mounting hardware
- Strain relief and cord anchorage effectiveness at the junction box entry
- Connector retention force and securement of locking couplings
- Post-test electrical integrity, including continuity, wet leakage current, and dielectric withstand behavior
- Visual evidence of damage such as conductor exposure, insulation cut-through, potting cracks, or displacement of the cable relative to its anchorage
Testing Methods
Specimen Preparation and Conditioning
Specimens are conditioned under standard laboratory ambient conditions, typically 25 °C ± 5 °C, and inspected beforehand to confirm that terminations are complete and correctly assembled. Loads are applied with calibrated force gauges, clamps, and torque tools using fixtures that grip the cable or terminal without damaging the conductor, and each force is applied gradually and held for the duration stated in the standard, commonly around 10 seconds.
Pull Test (IEC 60068-2-21, Test Ua)
A steadily increasing tensile force is applied along the axis of each external cable or lead. The magnitude is selected from the force table of IEC 60068-2-21 according to conductor cross-sectional area; for the 4 mm² to 6 mm² output cables used on most utility-scale modules, forces in the order of tens of newtons, frequently around 40 N held for approximately 10 seconds, are typical. The test reveals weak crimps, inadequate strain relief grip, and insufficient potting adhesion.
Push Test (Test Ua2)
An axial compressive force is applied to terminals and pins to simulate insertion loads and mishandling during installation. The termination must show no loosening, displacement, or penetration damage that could compromise clearances and creepage distances.
Bending Test (Test Ub)
A defined bending moment, commonly in the range of 0.2 N·m to 0.5 N·m depending on conductor size, is applied to each lead through a prescribed number of bending cycles at a specified angle. This procedure exposes fatigue-sensitive points such as the cable exit from the box and the conductor entry into a connector.
Torque Test (Test Uc)
Screw-type terminals are tightened and loosened several times with the torque values specified for the thread size, then re-torqued and load tested. The hardware must not strip, and the terminal must continue to clamp the conductor securely without deformation of insulating parts.
Strain Relief Evaluation (IEC 61730-2, MST 22)
The cable anchorage is subjected to combined pull and torsional loading, after which the longitudinal movement of the cable relative to the anchorage is measured. Acceptance criteria commonly limit displacement to a few millimeters, for example 2 mm, and require that the conductors inside the box remain free of tensile stress.
Post-Test Assessment
After mechanical loading, specimens undergo visual inspection in accordance with the applicable inspection criteria, verification of electrical continuity, and, where required by the test plan, a wet leakage current test (MQT 03 in IEC 61215-2, MST 17 in IEC 61730-2) and a dielectric withstand check (MST 16). A termination passes only when no visible damage occurs, no conductor breaks or loosens, and all subsequent electrical safety requirements remain satisfied.
Applications
- Design qualification and type approval of new module families under the IEC 61215 series
- Safety certification and market access under IEC 61730, UL 61730, and the aligned GB/T national standards
- Supplier qualification and incoming inspection of junction boxes, cables, and connectors by module manufacturers
- Research and development of potting compounds, adhesives, and strain relief geometries
- Root-cause failure analysis after field incidents involving detached cables or failed terminations
- Periodic quality surveillance and batch sampling for utility-scale power plant procurement
- Comparative benchmarking of termination designs by accredited third-party laboratories
FAQ
Question: Which standards define PV module termination strength testing?
Answer: The core references are IEC 61215-2 (test MQT 14), which calls up the mechanical procedures of IEC 60068-2-21 Test U, and IEC 61730-2 (test MST 22) for strain relief. UL 61730, GB/T 9535, and GB/T 20047 contain equivalent or aligned national requirements.
Question: Is the test destructive?
Answer: The applied loads can permanently damage a marginal termination, so specimens are treated as consumed for qualification purposes. A well-designed module, however, should show no lasting damage when the specified forces are applied.
Question: What are the pass criteria?
Answer: A termination passes if no conductor breaks or loosens, no insulation damage or cable slippage beyond the permitted displacement occurs, the junction box remains securely attached, and continuity plus subsequent wet leakage and dielectric tests are all satisfied.
Question: Can the test be performed at component level instead of on full modules?
Answer: Yes. Junction boxes and cable assemblies are routinely tested mounted on representative laminate sections. Component-level results are valuable for supplier control, but full qualification of a module family requires testing the complete product as shipped.
Question: Why do cables need both pull and bending tests?
Answer: Pull testing reproduces steady axial loads such as cable tensioning during installation, while bending tests reproduce the repeated flexing caused by wind vibration and thermal movement. The two loading modes activate different failure mechanisms, so both are necessary.
Question: How long does termination strength testing take?
Answer: The mechanical loading itself is quick, typically completed within a few hours for a full module. When post-test electrical verification such as wet leakage measurement is included, most projects are completed within one to three working days at accredited third-party laboratories.
