Photovoltaic Module Lead-Out Terminal Strength Testing: Standards, Methods, and Quality Requirements

Photovoltaic module lead-out terminal strength testing evaluates the mechanical robustness of a solar panel's output terminations, cables, and connectors against the pulling, bending, and torsional stresses encountered during installation and long-term outdoor service. Performed in accordance with IEC 61215-2 (test MQT 14) and IEC 60068-2-21, it is a mandatory element of PV module design qualification and type approval in accredited third-party laboratories. This article explains the applicable standards, sample requirements, test items, methods, acceptance criteria, and typical applications of terminal strength testing for photovoltaic modules.

Technical Overview

The lead-out terminals of a photovoltaic (PV) module—including junction box output terminals, flying leads with couplers, terminal blocks, and cable entry systems—represent one of the most mechanically stressed interfaces of the entire product. During transportation, installation, and decades of field operation, these terminations are subjected to tensile loads, bending from wind-induced vibration, torsion during connector mating, and repeated thermal expansion and contraction. A failed termination can interrupt the module circuit, generate arcs and hot spots, and ultimately create a fire hazard.

Lead-out terminal strength testing, often referred to as the "robustness of terminations" test, is therefore a core mechanical evaluation within PV module qualification. For terrestrial PV modules, the governing requirement is IEC 61215-2 (test MQT 14, "Robustness of terminations"), which delegates the detailed procedures to IEC 60068-2-21 (environmental testing, Part 2-21, Test U: robustness of terminations and integral mounting devices). The safety standard IEC 61730-2 imposes additional strain relief and cable anchorage requirements, while component-level standards such as IEC 62790 (junction boxes) and IEC 62852 (connectors) specify corresponding tests at the component level. Equivalent GB/T national standards aligned with the IEC 61215 series apply in the Chinese market.

Depending on the termination type, the test program may include the following sub-tests defined in IEC 60068-2-21:

• Test Ua — tension (pull) applied along the axis of the termination
• Test Ub — repeated bending of leads in alternating directions
• Test Uc — stress relief test to verify that external loads are not transmitted to internal connections
• Test Ud — torque test for snap-in type terminations
• Test Ue — bending stress test for terminations with soldered connections

Only the sub-tests relevant to the termination construction present on the sample are applied, and the tests are conducted in the sequence prescribed by the applicable product standard.

Testing Samples

Complete Photovoltaic Modules

Full-size modules representing routine production are used for the module-level qualification test. Both crystalline silicon modules and thin-film modules within the scope of the IEC 61215 series are eligible. Samples must incorporate the junction box, output leads, connectors, or terminal blocks exactly as shipped commercially, since any deviation in mounting, potting, or crimping invalidates the mechanical evaluation. Prior to testing, samples are conditioned in a standard laboratory atmosphere (typically 23 °C ± 5 °C) as required by the test plan.

Junction Box Assemblies

Component-level evaluations are performed on junction box assemblies in accordance with IEC 62790. Samples include the box body, terminal inserts, bypass diodes if applicable, and cable glands, fitted with the manufacturer-specified cable type, conductor size, and crimp contacts. These tests verify the integrity of the terminal retention system and the cable anchorage independently of the laminate.

Cable Assemblies and Connector Systems

Lead sets assembled with PV cables (such as those conforming to EN 50618 or IEC 62930) and couplers conforming to IEC 62852, or UL 6703-listed connectors for the North American market, may be tested separately. This is common during supplier qualification, design changes, or when verifying the compatibility of a connector system with a specific junction box.

Testing Items

A complete lead-out terminal strength evaluation typically comprises the following test items:

• Tensile (pull-out) strength of terminations, leads, and crimped contacts
• Bending and flexural endurance of output leads under repeated deflection
• Torque resistance of screw-type terminals and snap-in terminations
• Stress relief performance to prevent load transfer to internal joints
• Cable anchorage (strain relief) at the junction box entry under pull, push, and torsion
• Post-test electrical verification, including continuity, insulation resistance, and where required, wet leakage current testing

The specific items selected depend on the termination construction: modules with flying leads emphasize tension, bending, and cable anchorage, whereas modules with screw terminals emphasize torque and stress relief testing.

Testing Methods

Tensile Test

A calibrated universal testing machine or dedicated pull fixture applies a gradually increasing axial force to the termination or lead, aligned with the conductor axis. The force magnitude and hold duration are selected from the tables of IEC 60068-2-21 according to the nominal cross-sectional area of the conductor; for the conductor sizes commonly used on PV module leads (approximately 1.5 mm² to 6 mm²), the specified forces are on the order of tens of newtons. The force is maintained for the prescribed duration, after which the sample is examined for conductor pull-out, wire strand breakage, or displacement of the termination.

Bending Test

In the bending test, the lead is deflected through a defined angle (approximately 45 degrees) at a controlled rate, with a prescribed mass or force acting on the conductor. The bending is repeated for the specified number of cycles, alternating between two perpendicular planes. The test reproduces the fatigue loading produced by wind-induced vibration and cable movement, and the sample is subsequently inspected for cracked insulation, broken strands, and loosened terminals.

Torque and Stress Relief Tests

For terminations with screw-type clamps, a defined torque based on the thread diameter is applied and released to confirm that conductors are securely retained without damage. The stress relief test verifies that external mechanical loads applied to the lead do not propagate into the terminal interior or internal soldered connections, which is essential for preventing intermittent contacts over the module lifetime. Snap-in terminations are additionally subjected to the dedicated torque sub-test where applicable.

Cable Anchorage and Strain Relief Test

At the component level, IEC 62790 and IEC 62852 prescribe push, pull, and torsion loading at the cable entry of the junction box or connector body. After testing, the axial displacement of the cable must remain within the small limits allowed by the standard, and the insulation and conductors must remain undamaged, confirming that the gland or clamping system reliably absorbs external loads.

Acceptance Criteria and Post-Test Evaluation

A sample passes the test when no mechanical damage occurs that could impair the normal operation or safety of the module: no broken or detached external leads, no cracked insulation, no loosened or pulled-out terminals, and no interruption of electrical continuity. The module is then subjected to visual inspection in accordance with IEC 61215-2 (MQT 01) to confirm the absence of major defects, and insulation-related measurements such as wet leakage current (MQT 03) are repeated where the qualification sequence requires. Component samples are assessed against the pass criteria of the corresponding clauses of IEC 62790 or IEC 62852.

Applications

Lead-out terminal strength testing supports a wide range of engineering and quality activities across the photovoltaic value chain:

• Design qualification and type approval of PV modules under IEC 61215 and IEC 61730, carried out in accredited third-party laboratories for market access in Europe, Asia, and the Americas
• Factory quality control, including periodic requalification after junction box, cable, connector, or process changes
• Research and development of bonding and potting processes for junction box attachment, optimization of crimp tooling, and validation of lead routing designs
• Comparative supplier evaluation of junction boxes, PV cables, and connector systems during sourcing decisions
• Failure analysis of field returns, such as fatigue fracture of leads, connector separation, or arcing damage traced to inadequate terminal retention
• Verification of special products exposed to elevated mechanical stress, including building-integrated PV, flexible modules, vehicle-integrated PV, and marine or high-vibration installations

FAQ

Which standard governs lead-out terminal strength testing for PV modules?

Module-level testing is governed by IEC 61215-2, test MQT 14, which applies the procedures of IEC 60068-2-21 (Test U). Related requirements appear in IEC 61730-2 for module safety, and in IEC 62790 and IEC 62852 for junction boxes and connectors respectively. Corresponding GB/T national standards aligned with IEC 61215 apply in China.

What forces are applied during the test?

Tensile forces are selected from the tables of IEC 60068-2-21 according to conductor cross-sectional area, typically amounting to tens of newtons for common PV lead sizes. Bending is performed through an angle of approximately 45 degrees for a specified number of cycles, and defined torques are applied to screw or snap-in terminals based on their dimensions.

What are the pass and fail criteria?

A sample passes if all terminations remain intact and functional: no conductor breakage or pull-out, no insulation cracking, no loosened hardware, and no transfer of stress that damages internal connections. The module must remain free of major defects under visual inspection, and required electrical safety measurements, such as wet leakage current, must continue to be met.

How many samples are required?

For module qualification, the robustness of terminations test is typically performed on one module drawn from the qualification test batch, as specified in the test sequence of IEC 61215-2. Component-level testing according to IEC 62790 or IEC 62852 uses the number of dedicated component samples stated in those standards.

Why is terminal strength important for module safety?

A degraded termination increases contact resistance, which can produce localized heating, arcing, or ground faults—recognized contributors to PV system fires. Verifying terminal strength therefore protects not only energy yield and system availability but also the overall safety of the installation.

Can the test be combined with other environmental tests?

Yes. Within the IEC 61215-2 qualification sequence, the robustness of terminations test is scheduled relative to other tests as defined by the standard. Combined programs—for example, terminal testing after extended thermal cycling or damp heat exposure—are also used in reliability studies to simulate aged interconnection systems.