PV Module Lead-Terminal Strength Testing: Standards, Methods, and Acceptance Criteria

The lead-terminal strength test for photovoltaic modules verifies that junction box terminals, output cables, and connector systems can withstand the pull, bend, and torque forces encountered during manufacturing, transportation, installation, and long-term outdoor operation. Rooted in IEC 61215-2 (test MQT 14) and the underlying procedures of IEC 60068-2-21, it is a mandatory element of design qualification and safety certification for both crystalline silicon and thin-film PV modules. This article explains the test principle, applicable standards, sample requirements, test items, procedures, acceptance criteria, and practical applications of terminal strength testing.

Technical Overview

The lead-terminal strength test — designated MQT 14 in IEC 61215-2 and also known as the termination robustness or terminal stress test — evaluates the ability of a photovoltaic module's electrical output terminations to resist mechanical loading. Terminations include the screw, spring, or soldered terminals inside the junction box, the output cables ("flying leads") and their entry glands, and the mating connector systems through which the module delivers DC power to the array.

Throughout module production, transport, installation, and more than 25 years of field service, these terminations are exposed to tensile pulls, bending, twisting, vibration, and thermal cycling. Insufficient terminal strength can cause conductor breakage, insulation cracking, loosened screw connections, or cable pull-out. These failure modes increase contact resistance, create hot spots, and may ultimately lead to DC arcing and fire. Terminal strength testing therefore functions as an essential screen for both mechanical integrity and electrical safety.

The module-level method is defined in IEC 61215-2, which delegates the detailed loading procedures to IEC 60068-2-21 (environmental testing, Part 2-21: Test U — robustness of terminations and attachments). Corresponding safety requirements, including strain relief and cable securement, are specified in IEC 61730-2. In China, GB/T 9535 adopts the IEC 61215 methodology, while UL 61730 covers the equivalent safety scope in North America. Component-level requirements for the parts making up the termination path are found in IEC 62790 (junction boxes), IEC 62852 (connectors), and IEC 62930 (photovoltaic wires).

Testing is typically performed at room ambient conditions (commonly 23 °C ± 5 °C unless otherwise specified) using calibrated force and torque equipment, either by accredited third-party laboratories during certification or by manufacturers' in-house facilities during development and quality control.

Testing Samples

Complete PV Modules

Representative production modules — crystalline silicon (monocrystalline, PERC, TOPCon, HJT) or thin-film technologies — fitted with junction boxes and factory-attached output leads. Framed glass/backsheet and frameless glass/glass constructions can both be evaluated, as their termination designs differ.

Terminations and Lead Assemblies

Junction boxes with or without pre-terminated cables, plug-in DC couplers, terminal blocks, and lug-type connections as mounted on the module. All distinct termination types present on a module should be subjected to the applicable loads.

Component-Level Samples

When certifying components independently, junction boxes, connectors, and cables may be tested on representative mounting fixtures in accordance with IEC 62790, IEC 62852, and IEC 62930 respectively. Module-level testing remains necessary for full design qualification, because installation, potting, and mounting stresses cannot be fully reproduced at component level.

Sample quantity, selection, and conditioning follow the test plan of the applicable standard; IEC 61215-2 defines specific sample allocation rules, and the terminal strength test may be combined with other tests within the qualification sequence where permitted.

Testing Items

Depending on the termination type and the applicable standard, the following items are covered by lead-terminal strength evaluation:

• Axial tensile (pull) strength of lead terminations and cable assemblies
• Bending resistance of flexible leads in multiple directions for a prescribed number of cycles
• Twist (torque) robustness of leads and torque endurance of screw terminals
• Strain relief and cable securement at the junction-box entry
• Mechanical security and pull-out resistance of mated connector systems, cross-referenced to IEC 62852 where applicable
• Post-test verification: visual inspection, electrical continuity, and, where the test sequence requires, insulation or wet leakage current assessment

Testing Methods

All loads are applied gradually with calibrated force gauges, torque tools, or motorized test rigs, and each termination is evaluated against the pass criteria of the governing standard. The principal procedures are as follows.

Pull (Tension) Test

In accordance with IEC 60068-2-21 Test Ua, an axial force is applied to the termination along the direction of the lead, increased gradually to the specified value, and held for a defined short duration (typically 10 seconds). The required force scales with conductor cross-sectional area and the manufacturer's declared rating; for common PV lead sizes, applied pull loads are typically in the range of tens of newtons.

Bend Test

Following Test Ub, flexible leads are bent through a specified angle alternately in different directions for a prescribed number of cycles, simulating handling, cable routing, and installation stresses. The procedure verifies that conductors, insulation, and crimp or solder joints inside the termination are not damaged by repeated flexing.

Torque Tests

Test Uc and related procedures apply twisting torque to leads and tabs, while screw terminals and threaded fasteners are subjected to defined tightening and loosening cycles. The purpose is to confirm that clamping mechanisms remain effective, terminal hardware does not deform or loosen, and conductors are not severed or pinched.

Strain Relief and Cable Securement

Under the safety requirements of IEC 61730-2, the cable is subjected to repeated pulls and twists at levels appropriate to its size and construction. The cable must not shift beyond the permitted displacement at the gland, the jacket must not be cut through or abraded at the entry, and no tensile load may be transmitted to the internal conductor connections.

Acceptance Criteria

After testing, the module is visually inspected against the major-defect criteria of IEC 61215-1. Typical pass requirements include: no broken or exposed conductors, no cracked insulation that compromises electrical safety, no loosened or withdrawn terminations, intact junction-box attachment, and maintained electrical continuity. Where the test sequence specifies, affected modules must additionally pass wet leakage current or dielectric tests to confirm that insulation integrity was not degraded.

Applications

Lead-terminal strength testing supports every stage of the module product life cycle:

• Design qualification and type approval under the IEC 61215 test sequence
• Safety certification under IEC 61730 series and UL 61730 requirements
• Requalification after engineering or bill-of-material changes, such as a new junction box, cable, or connector supplier
• Factory quality control, surveillance audits, and periodic verification of certified production
• Research and development of lightweight, flexible, building-integrated, and vehicle-integrated PV products, where terminations experience greater mechanical motion
• Failure analysis and forensic investigation of field returns involving connector or lead damage
• Bankability studies, tender submissions, and insurance documentation requiring demonstrated mechanical robustness

FAQ

What is the purpose of the lead-terminal strength test?

It confirms that a module's electrical terminations can withstand the mechanical stresses of manufacturing, installation, and field operation without conductor breakage, insulation damage, or loosening — conditions that could otherwise cause high resistance, hot spots, DC arcing, or fire.

Which standards govern the test?

IEC 61215-2 defines the module-level test (MQT 14) and references IEC 60068-2-21 for the detailed loading procedures. IEC 61730-2 adds safety-oriented strain relief and cable securement requirements. GB/T 9535 and UL 61730 provide corresponding national and regional coverage, while IEC 62790, IEC 62852, and IEC 62930 address the component level.

What loads are applied during the test?

Loads depend on conductor size and termination type. Pull forces typically fall in the tens of newtons for common PV leads, and bending and torque values are selected from the tables of IEC 60068-2-21 or the applicable safety standard. The manufacturer's declared terminal rating also defines the minimum withstand levels.

Is the test destructive?

It is potentially damaging, and tested modules are generally not returned to commercial service. However, IEC 61215-2 permits terminal strength testing to be performed on modules that continue within the qualification sequence, subject to the standard's sample allocation rules.

What are the most common failure modes?

Typical failures include cable pull-out from the gland, jacket damage at the junction-box entry, conductor fracture after repeated bending, loosening of screw terminals, and separation of mated connectors. Any of these findings constitutes a test failure if they compromise safety or functionality.

How can manufacturers improve pass rates?

Effective measures include robust strain-relief and gland design, verified crimping and potting processes, incoming inspection of junction boxes and connectors against component standards, and design margins above the minimum required force and torque levels.

Where can the test be performed?

Accredited third-party laboratories perform the test for certification purposes using calibrated force and torque equipment, while manufacturers' in-house laboratories commonly conduct it during product development and routine quality control.