Quality Assurance

What is the purpose of mechanical testing? Power cables, typically installed underground, in ducts, or on overhead structures, are often subject to mechanical stresses such as tension, compression, bending, and twisting. Hence it is important that cables are put through stringent tests to ensure they can withstand the mechanical stresses that they will be subjected to during installation, operation, and maintenance. One of the categories we test for in mechanical testing, is the Tensile Elongation test, which affirm that cables manufactured are equipped with mechanical capabilities including flexibility and load-bearing capabilities. By subjecting the cable’s insulation and sheath to tensile elongation test, we can compare it against predetermined minimum elongation and tensile strength based on standards to identify potential weaknesses in the cable’s design or materials to optimise performance. This is fundamental to providing our customers with reliable cables. As cables are meant to operate over a lifespan of 20 to 30 years under normal use conditions, how can we ensure that cables continue to retain mechanical integrity even after long term use? The Tensile Elongation Test We subject our cables to Tensile Elongation to determine whether they can retain tensile strength and elongation after being exposed to a tension load. This assessment determines the cable’s ability to maintain mechanical integrity at ambient temperatures, and is one of the key mechanical tests our cables need to withstand. In this test, a tubular or dumb-bell control sample is prepared and placed in an electromechanical or universal testing machine with 2 clamps and pulled from each end until its breaking point. The test measures the amount of force (N) applied and elongation when the sample breaks (∆L).  Tensile strength – Amount of force (N):  Strength needed to pull the material of the cable until it breaks. The maximum strength it can tolerate Elongation(∆L):  The length that the material of the cable can be stretched until it breaks Subsequently, the control sample is used as a baseline and compared with an aged sample placed in the oven and thereafter subjected to the Tensile Elongation test. Read on to find out more about how we age cable samples. Ageing Conditions Samples To ensure that the cables can maintain mechanical integrity over a 20–30-year lifespan, we subject the materials to accelerated ageing conditions to verify that prolonged use does not negatively affect the cable. It is important to conduct comparison tests with non-aged samples after an accelerated ageing process. To perform the ageing test, the cable is placed in an oven to accelerate the ageing process, simulating decades of usage. This is in line with IEC 60811- 401:2012 standards, which typically applies to crosslinked and thermoplastic compounds used for insulating and sheathing materials in the ageing oven process. The samples placed in the oven are called aged samples. The Importance of Testing  A successful outcome provides assurance that the cables will have a long and reliable service life, which is critical for the safe, efficient operation of electrical power systems, and minimise waste as a result of cable longevity. If a cable is unable to withstand mechanical testing, it can lead to unsafe situations at project sites.  At Keystone Cable, mechanical testing is a standard component of our cable testing regimen. This is our assurance to you that our cables are reliable and adhere to international specifications.   For more information, please reach out to our sales team.

In our previous Keystone Academy blog, ‘What is the Difference Between FRT and FR Cable?’, we shared that Fire Resistant (FR) cables are fire safety products which maintain circuit integrity in the presence of fire, while Flame Retardant (FRT) cables reduce the spread of fire. This is critical so that life-saving electrical installations, such as fire alarms, smoke detectors, PA systems, and emergency lighting, can perform their functions in the event of a fire. Keystone low-smoke, zero-halogen (LSZH) flame retardant (FRT) cables comply with IEC 60332, IEC 60754, and IEC 61034, which ensure that the flame retardant cables reduce flame propagation, prevent the release of toxic gases, and control smoke emission under fire conditions. This article breaks down the standard LSZH FRT test methods in more detail. Flame Propagation Tests: IEC 60332-1-2, IEC 60332-3 Flame retardant cables prevent flame propagation during a fire emergency. The cable’s protective material includes additives such as aluminium hydroxide or magnesium hydroxide. When the material comes into contact with fire, the byproduct from the endothermic reaction is gaseous water which will help envelop the flame and thereby exclude oxygen from the fire. IEC 60332-1-2 is the test for vertical flame propagation for a single insulated wire or cable. During the test, a single-core cable with a length of approx. 0.6m is mounted vertically using two clamps, and a flame is applied to the bottom end for 60 seconds (or 120 seconds if the cable’s overall diameter is >25mm). Passing Criteria: After removing the flame, the burning cable extinguishes itself, and the fire damage is at least 50mm below the upper mounting clamp. IEC 60332-3 tests vertical flame spread of vertically mounted bunched wires or cables. This test is conducted as it cannot be assumed that bunched cables will behave the same way in the fire as single cables. This is because flame propagation along a vertical bunch of cables depends on other factors, such as the volume of combustible material exposed and the geometrical configuration of the cables. Passing Criteria: After the burning ceased, the charred portion does not exceed a height of 2.5 meters. Acid Gas Emission Tests: IEC 60754 When fire comes into contact with polyvinyl chloride (PVC) or other chlorine-containing materials, hydrogen chloride gas is released. Hydrogen chloride gas forms corrosive hydrochloric acid (HCl) on contact with water found in body tissues. This irritates the eyes, mouth, throat, nose, and lungs, thus making escape more difficult. At Keystone Cable, all our fire-resistant and flame-retardant cables use Low Smoke Zero Halogen (LSZH) compounds to prevent the formation of HCl gases from burning cables. International standard IEC 60754 specifies tests for determining the degree of acidity of gases generated during the combustion of materials from electric cables by measuring the pH and conductivity. Passing Criteria: The weighted pH value is not less than 4.3 when related to 1 litre of water, and the weighted value of conductivity is not more than 10μS/mm when related to 1 litre of water. Smoke Emission Tests: IEC 61034 This test measures the smoke density of electric cables burning under defined conditions. The “3-meter cube test” measures the amount of smoke generated by cables in the event of a fire. The cables are placed in a 3m3 enclosure. A tray containing alcohol is supported above the ground surface to permit air circulation around and beneath the tray. The test pieces (cables or bundles) touched horizontally and centred above the tray. Air circulation will begin, and the alcohol (1 litre) will be ignited. A beam of light is transmitted from one window of the chamber to the opposite window. The light intensity is measured between the light source and the photocell. The test is considered done when there is no decrease in light transmittance for 5 minutes after the fire source has been extinguished or when the test duration reaches 40 minutes. Passing Criteria: The recorded light transmittance is at a minimum 60%, which means the smoke density has a maximum value of 40%. For more information, please contact our team. Contact Sales In our previous Keystone Academy blog, ‘What is the Difference Between FRT and FR Cable?’, we shared that Fire Resistant (FR) cables are fire safety products which maintain circuit integrity in the presence of fire, while Flame Retardant (FRT) cables reduce the spread of fire. This is critical so that life-saving electrical installations, such as fire alarms, smoke detectors, PA systems, and emergency lighting, can perform their functions in the event of a fire. Keystone low-smoke, zero-halogen (LSZH) flame retardant (FRT) cables comply with IEC 60332, IEC 60754, and IEC 61034, which ensure that the flame retardant cables reduce flame propagation, prevent the release of toxic gases, and control smoke emission under fire conditions. This article breaks down the standard LSZH FRT test methods in more detail.   Flame Propagation Tests: IEC60332-1-2, IEC60332-3 Flame retardant cables prevent flame propagation during a fire emergency. The cable’s protective material includes additives such as aluminium hydroxide or magnesium hydroxide. When the material comes into contact with fire, the byproduct from the endothermic reaction is gaseous water which will help envelop the flame and thereby exclude oxygen from the fire. IEC 60332-1-2 is the test for vertical flame propagation for a single insulated wire or cable. During the test, a single-core cable with a length of approx. 0.6m is mounted vertically using two clamps, and a flame is applied to the bottom end for 60 seconds (or 120 seconds if the cable’s overall diameter is >25mm). Passing Criteria: After removing the flame, the burning cable extinguishes itself, and the fire damage is at least 50mm below the upper mounting clamp. IEC 60332-3 tests vertical flame spread of vertically-mounted bunched wires or cables. This test is conducted as it cannot be assumed that bunched cables will behave the same way in the fire as single cables. This is because flame propagation along a vertical bunch of cables depends on other factors, such as the volume of combustible material exposed and the geometrical configuration of the cables. Passing Criteria: After the

What is the purpose of cable insulation? Cable insulation is an important protective material for cable conductors. It is non-conductive, used to resist electrical leakage, prevents cable conductors from contact with other conductors, and protects the conductor from environmental threats such as heat, water, and chemicals. Poor or damaged insulation may result in short circuit, electric shock, or fire. Because the insulation of a cable is so important in determining the cable’s safety and electrical conductivity, at Keystone Cable, we ensure that all our cables are subject to passing the insulation resistance (IR) test (as part of our many tests) before product delivery to customers. What is Insulation Resistance (IR) Test? An insulation resistance (IR) test measures the resistance to current flow across it on a completed cable; it applies a test voltage to determine how effective the insulation is in preventing the flow of electric current out of the insulation. This is analogous to how you would pump pressurized water in a water pipe to identify leaks. Since insulation starts to age after it is made, over time, the performance of a high quality insulation material versus one of lower quality will become more apparent. Hence it is important that after the cable is manufactured there is a good pass rate for the IR test to help ensure the longevity of your cable. Insulation Resistance Test Process IR test is conducted using an IR tester. The IR tester is a portable ohmmeter (MΩ.km) with a built-in generator that produces a high DC voltage. The DC voltage usually measures 500V and causes a current to flow around the surface of the insulation. This resistance reading measures leakage current; a high IR reading means very little current is escaping through the insulation and a low IR reading indicates stronger current leakage and may indicate a break in the insulation. At Keystone’s quality control laboratory, we adhere to International Standards IEC 60502-1 for our IR tests. To pass, the cables would need to obtain a minimum insulation resistance constant Ki (refer to the table below) while tested at its maximum operating temperature (e.g. 70 °C for PVC insulated cables and 90 °C for XLPE and rubber insulated cables). For single core cables, the cables are tested in water while for multi core cables they are tested in air. Test results will also vary for cables across different types of insulation, length of run and ambient temperature. To be certain for your cable type, feel free to check in with our team on the IR tests we perform for your cables.