Cable flexibility in bending test

Cable Flexibility in Bending Test – Accredited ISO/IEC 17025 Testing Services for the Colombian Market

Cable flexibility in bending is a critical mechanical property that determines the performance, durability, and safety of electrical cables, flexible cords, communication cables, and fiber optic cables used in a wide range of applications, from automotive wiring and industrial machinery to construction, aerospace, and consumer electronics. A cable that fails to maintain its integrity during repeated bending cycles can suffer conductor breakage, insulation damage, loss of signal transmission, short circuits, and even fire hazards. In the Colombian market, where the Superintendencia de Industria y Comercio (SIC), the Ministerio de Minas y Energía (MinMinas), and the Reglamento Técnico de Instalaciones Eléctricas (RETIE) impose strict quality and safety requirements for electrical products, the accurate evaluation of cable flexibility in bending is essential for product certification, quality control in manufacturing, homologation of components, and import and export processes. Our laboratory offers a comprehensive testing service for cable flexibility in bending, applying standardized methods that simulate real-world bending conditions, measure the number of bend cycles to failure, determine the minimum bending radius, and assess the integrity of conductors, insulation, and sheathing after flexing. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Colombian authorities, including the Dirección de Impuestos y Aduanas Nacionales (DIAN) and the Superintendencia de Industria y Comercio (SIC), making them essential for product certification, quality assurance, and market access in Colombia.

Cable Samples We Regularly Test

Our laboratory receives a wide variety of cables and flexible components for bending flexibility testing. Typical samples include:

• Electrical power cables – with PVC, XLPE, EPR, rubber, and silicone insulation, of various cross-sectional areas (from 0.5 mm² to 240 mm²), for low, medium, and high voltage applications.
• Flexible cords and extension cables – for household appliances, power tools, and temporary electrical installations.
• Communication and data cables – coaxial cables, twisted pair cables (e.g., Cat5e, Cat6, Cat7), and optical fiber cables.
• Automotive and aerospace cables – with thin-wall insulation, high-temperature resistance, and specialized shielding.
• Control and instrumentation cables – with multiple conductors and shielding, used in industrial automation and process control.
• Welding cables and battery cables – with highly flexible conductors and robust insulation for heavy-duty applications.
• Armored and flexible metallic conduits – for mechanical protection of cables in harsh environments.
• Prototype and new cable designs – submitted by manufacturers for validation of bending flexibility and durability before series production.
• Used or aged cable samples – extracted from field installations, for analysis of remaining service life and degradation of flexibility.

Flexural Endurance Testing – Repeated Bending and Flexing

The flexural endurance test evaluates the ability of a cable to withstand repeated bending, flexing, and reversing bending cycles without failure of the conductors or insulation. Our methods simulate the real-world conditions that cables experience during installation, operation, and movement, following international standards and the requirements of the RETIE and SIC for cable certification.

• Repeated bending test (IEC 60227-2 / NTC 5300 – for flexible cords and cables) – a cable sample is clamped at one end and subjected to repeated bending around a mandrel of specified radius (typically 10 to 25 times the cable diameter) at a controlled frequency (0.5 to 2 Hz) for a specified number of cycles (10,000 to 100,000 cycles). The test is performed under a specified tensile load (generally 10 N to 100 N, depending on the cable cross-section). The cable is monitored for conductor breakage (detected by electrical continuity), insulation cracking, and sheath damage. We report the number of cycles to failure, the type of failure (conductor breakage, insulation cracking), and the test conditions.
• Flexing test for cables in automotive and robotic applications (ISO 1458 / NTC 5301 – for flexible cables with high flex life) – the cable is subjected to a bending radius of 10 times the cable diameter, at a rate of 60 bends per minute, under a specified tension (e.g., 50 N). The test continues until a conductor break or insulation failure occurs. We report the flex life (number of cycles) and the failure mode. This test is critical for cables used in robotic arms, automotive harnesses, and moving machinery.
• Reversing bending test (ASTM D4169 / NTC 5302 – for cables with reverse bending) – the cable is alternately bent in opposite directions (e.g., +90° to -90°) around a mandrel at a frequency of 0.5 Hz, under a specified tensile load. The test is performed for a predetermined number of cycles (e.g., 10,000 cycles) or until failure. We report the number of cycles to failure and the observed damage.
• Flexing test at different temperatures (IEC 60227-2 – variant, NTC 5303) – the flexing test is performed at -10 °C, 23 °C, and 40 °C to evaluate the effect of temperature on cable flexibility, which is particularly relevant for cables used in the diverse climatic conditions of Colombia (from cold Andean regions to hot coastal areas). We report the flex life and failure mode at each temperature.
• Flexing test with varying loads (NTC 5304 – method of variable tensile load during bending) – the test is performed with a tensile load that varies cyclically (e.g., from 0 to 50 N) while bending, simulating the dynamic loads experienced by cables in moving machinery. We report the flex life under varying load conditions.

Minimum Bending Radius Test – Evaluating the Cable's Ability to Bend without Damage

The minimum bending radius is the smallest radius around which a cable can be bent without sustaining damage to its conductors, insulation, or sheath. This parameter is essential for proper cable installation and for ensuring long-term reliability. Our tests determine the minimum bending radius for cables of various types and constructions, following international standards and the installation requirements of the RETIE.

• Mandrel bending test (ASTM D412 / NTC 5310 – for cables and flexible cords) – the cable is bent around a series of mandrels of decreasing radius (from 20 times the cable diameter down to the manufacturer's specified minimum radius). The cable is visually inspected for kinking, cracking, or damage to the insulation after each bend. The minimum bending radius is the smallest radius at which no damage occurs. We report the minimum bending radius (in mm or as a multiple of the cable diameter).
• Bend test with a specified radius (IEC 60811-401 / NTC 5311 – for insulated cables) – the cable is bent around a mandrel of a specified radius (e.g., 10 times the cable diameter) and held for a specified time (e.g., 5 minutes), after which it is inspected for cracking, deformation, or damage. We report the condition of the cable after the bend test.
• Bending test at low temperatures (IEC 60811-504 / NTC 5312 – cold bend test) – the cable is conditioned at -15 °C or -20 °C for 4 hours, and then bent around a mandrel of specified radius (e.g., 5 times the cable diameter). The cable is inspected for cracking or damage. This test is critical for cables used in outdoor applications in cold regions of Colombia (e.g., Bogotá, Boyacá). We report the condition of the cable after the cold bend test.
• Bending test with visual and electrical inspection (NTC 5313 – combined method) – after the bending test, the cable is subjected to a dielectric strength test (1 kV, 50 Hz) to verify the integrity of the insulation, and a continuity test to verify the integrity of the conductors. We report the results of the electrical tests after bending.
• Bending radius test for fiber optic cables (IEC 60794-1-2 / NTC 5314 – for optical fiber cables) – the fiber optic cable is bent around a mandrel of specified radius, and the optical attenuation is measured before and after bending. An increase in attenuation of more than 0.5 dB indicates damage to the optical fibers. We report the bending radius, the increase in attenuation (dB), and the integrity of the optical fibers.

Torsion and Twist Testing – Evaluating Resistance to Rotational Forces

Cables are often subjected to torsional forces during installation and operation, especially in robotic arms, rotating machinery, and cable carriers. Our torsion tests evaluate the cable's ability to withstand twisting without damage to the conductors or insulation, following international standards and the requirements of the automotive and industrial sectors in Colombia.

• Repeated torsion test (IEC 60227-2 / NTC 5320 – for flexible cables) – the cable is twisted back and forth (e.g., ±180°) for a specified number of cycles (e.g., 5,000 cycles) at a frequency of 0.5 Hz, under a specified tensile load. The test is monitored for conductor breakage, insulation cracking, and sheath damage. We report the number of torsion cycles to failure and the failure mode.
• Torsion test at different temperatures (NTC 5321 – variant of torsion test at low and high temperatures) – the torsion test is performed at -10 °C, 23 °C, and 60 °C to evaluate the effect of temperature on the cable's resistance to torsion, which is relevant for cables used in diverse climatic conditions.
• Torsion test with visual and electrical inspection (NTC 5322 – combined method) – after the torsion test, the cable is subjected to a dielectric strength test (1 kV, 50 Hz) and a continuity test to verify the integrity of the insulation and conductors. We report the results of the electrical tests after torsion.
• Torsion test for cables in robotic applications (ISO 1458 – variant, NTC 5323) – the cable is subjected to a torsion angle of ±90° per cycle, at a rate of 60 cycles per minute, for 10,000 cycles. The test is performed under a tensile load of 20 N. We report the number of cycles to failure and the failure mode.

Bend and Flex Testing after Environmental Aging – Evaluating Long-Term Durability

Cables are exposed to heat, humidity, UV radiation, ozone, and chemicals during their service life, which can degrade their flexibility and increase the risk of failure. Our tests evaluate the effect of environmental aging on cable flexibility, simulating the conditions of the Colombian climate and industrial environments, and are essential for assessing the long-term durability of cables used in outdoor and harsh industrial settings.

• • Flexing test after thermal aging (ASTM D573 / ISO 188 / NTC 5330) – the cable is aged in an oven at 70 °C for 7, 14, and 28 days, and then subjected to the repeated bending test (IEC 60227-2). We report the reduction in flex life (number of cycles to failure) after thermal aging, and the retention of flexibility (%).
  • Flexing test after UV aging (ASTM G154 / NTC 5331 – UV exposure and flexing) – the cable is exposed to UV radiation (UVA-340) and condensation for 500 hours, and then subjected to the repeated bending test. We report the flex life after UV aging and the change in appearance (color, surface cracking).
  • Flexing test after ozone aging (ASTM D1149 / ISO 1431-1 / NTC 5332) – the cable is exposed to an ozone atmosphere (50 ppb) at 40 °C for 48 hours, and then subjected to the bending test. We report the condition of the cable after ozone exposure (cracking, brittleness) and the flex life.
  • Flexing test after immersion in chemicals (ASTM D471 / NTC 5333 – for cables exposed to oils and solvents) – the cable is immersed in mineral oil, hydraulic fluid, or a specified solvent for 7 days, and then subjected to the repeated bending test. We report the flex life after chemical exposure and the change in mass and hardness.
  • Flexing test after moisture and salt spray aging (ASTM B117 / NTC 5334 – for cables used in coastal areas) – the cable is exposed to salt spray for 240 hours, and then subjected to the bending test to evaluate the effect of corrosion on flexibility. We report the flex life after salt spray exposure and the presence of corrosion on conductors and shielding.

Complementary Tests – Conductor Integrity and Insulation Resistance after Flexing

To ensure that the cable's functionality is not compromised after bending, we perform complementary tests to verify the integrity of the conductors, the insulation, and the electrical characteristics of the cable. These tests are essential for the certification of cables used in safety-critical applications, such as in power distribution, control systems, and automotive wiring, and are required by the RETIE and the SIC for cable certification in Colombia.

• Conductor continuity test (IEC 60227-2 / NTC 5340) – after the bending test, a continuity test is performed with a multimeter (or a low-resistance ohmmeter) to verify that all conductors are intact and that there are no breaks. We report the continuity of the conductors.
• Insulation resistance test (ASTM D257 / NTC 5341 – megohmmeter test after bending) – after the bending test, the insulation resistance between the conductors and between the conductors and the sheath is measured with a 500 V or 1000 V megohmmeter. We report the insulation resistance (in MΩ), and verify that it exceeds the minimum requirements (typically > 100 MΩ for cables with PVC insulation).
• Dielectric strength test (IEC 60227-2 / NTC 5342 – high-voltage test after bending) – after the bending test, the cable is subjected to a dielectric strength test (2 kV, 50 Hz for 1 minute) between the conductors and between the conductors and the sheath, to verify that the insulation has not been damaged by flexing. We report the result of the dielectric test (pass/fail).
• Optical attenuation test for fiber optic cables (IEC 60794-1-2 / NTC 5343) – after the bending test, the optical attenuation of the fiber optic cable is measured and compared with the initial value. We report the increase in attenuation (dB) and verify that it is below the specified limit (typically < 0.5 dB).
• Visual and microscopic inspection of the flexed area (ASTM E1508 / NTC 5344 – SEM inspection of the cable cross-section) – the flexed area of the cable is examined visually and with a scanning electron microscope (SEM) to detect micro-cracks, conductor damage, separation of insulation layers, or fatigue of the conductor strands. We report the observations and any evidence of damage.
• Measurement of conductor resistance after bending (ASTM B193 / NTC 5345 – four-point probe method) – the resistance of the conductors is measured before and after the bending test, to detect any increase in resistance caused by cracking or thinning of the conductors. We report the resistance increase (%).

Test Report and Recognition in the Colombian Electrical Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (bending test machines, mandrels, megohmmeters, dielectric strength testers, etc.) and traceability to international standards (NIST, PTB). Our test reports are issued in Spanish and include:

• Full identification of the cable sample (type, manufacturer, lot, cross-section, insulation material, voltage rating, construction).
• Detailed description of the test method applied (IEC/ASTM/NTC standard, bending radius, load, frequency, temperature, number of cycles).
• Numerical results: number of bend cycles to failure, minimum bending radius (mm or as a multiple of cable diameter), insulation resistance (MΩ), dielectric strength (pass/fail), conductor continuity, and flex life retention after aging (%).
• Comparative tables against the values specified by the client or against the limits of the NTC 5300 (Repeated bending), NTC 5310 (Minimum bending radius), and the requirements of the RETIE and the SIC for cable certification.
• Photographs and micrographs (SEM) of the cable before and after the tests, showing cracks, damage, or failure points.
• Recommendations for design improvement (selection of more flexible insulation materials, increasing the strand count of conductors, optimizing the cable construction) and for proper installation and handling.
• Expanded uncertainty (k=2) for all key measurements (flex life, bending radius, insulation resistance), calculated according to the ISO/IEC 98-3 Guide.

These reports are fully accepted by the Superintendencia de Industria y Comercio (SIC) for product registration and quality certification, by the Ministerio de Minas y Energía (MinMinas) and the Retie for the verification of electrical safety standards, and by the Dirección de Impuestos y Aduanas Nacionales (DIAN) for tariff classification and quality verification in the import of cables and electrical components. Additionally, we offer consulting services for the selection of cables with high flexibility and durability, the optimization of cable designs for specific applications, and the implementation of quality control programs, contributing to the safety, reliability, and competitiveness of electrical products in the diverse and demanding Colombian market, from the coastal regions to the high-altitude Andean zones.