Keystone Academy

In our previous Keystone Academy blog, ‘What is the Difference Between FRT and FR Cable?’, we shared that Fire Resistant (FR) cables are a fire safety product, which means they not only reduce the spread of fire but will also maintain circuit integrity in the presence 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. In addition to complying with LSZH flame retardant (FRT) tests (IEC 60332, IEC 60754, and IEC 61034), LSZH FR cables are also tested to IEC 60331-21, BS 6387 or SS 299 to ensure that the fire-resistant cables maintain circuit integrity under fire conditions. In this article, we introduce the differences among the 3 common LSZH FR test standards. Resistance to Fire: SS 299 Singapore Standard SS 299 specifies tests for fire-resistant cables. This standard was updated in September 2021, and it is a modified adoption of British Standard BS 6387:2013, ‘Test method for resistance to fire of cables required to maintain circuit integrity under fire conditions’.  FR cables must pass protocols C, W, and Z test parameters to be considered fully compliant. For information on the old standard, SS 299-1:1998, refer to the blog “SS299:2021 Updates – Fire Resistant Test Standard”. Resistance to Fire: BS 6387 British Standards BS 6387 is the most commonly recognised FR cable test standard. Based on the latest standards update BS6387:2013, an FR cable is considered compliant only if it passes the BS 6387 Cat. CWZ requirement: • Resistance to fire alone, Category C (950 °C ±40 °C for 3 hours) • Resistance to fire with water, Category W (650 °C ±40 °C 15 mins flame, 15 mins water) • Resistance to fire with mechanical shock, Category Z (950 °C ±40 °C 15 mins flame, mechanical shock every 30s) Keystone Cable’s fire-resistant range complies with all of the above international standards. Contact us if you would like to find out more about the cable types to choose for your cabling requirement.

The conductor resistance (CR) test is basic, but one of the most important tests in quality testing of cables. It can verify whether the amount or quality of conductor material in a cable is sufficient. The CR test is done on either a complete length of cable or on a cable sample of at least 1m in length in accordance with IEC 60228. The test measures the DC resistance of the copper or aluminium conductor, which indicates how easily current can flow through the conductor; the higher the resistance, the less current flow. When the resistance is too high, the heat generated may cause premature insulation failure, resulting in a fire or short circuit. CR is influenced by the conductor dimensions, construction, temperature, and resistivity. Out of these factors, it is worth highlighting that because of the sensitivity of the reading to temperature, it is important to keep the sample in the test area for sufficient time to ensure that the conductor temperature has stabilized, which allows for an accurate test. The measured resistance is then converted to an equivalent resistance at standard temperature — 20°C according to IEC 60228 — and length. To ensure that the conductor resistance meets the standard, the observed resistance Rt is compared against the maximum conductor resistance at 20°C (R20) where: Rt = Observed Resistancekt = Temperature Correction Factor (Table 1)L = Length of the specimen in mR20 = Maximum Standard Resistance at 20°C (Table 2) If you come across a high conductor resistance reading (> R20), here are possible calculation adjustment factors to first consider before exploring actual conductor issues:  1. Incorrect conductor temperature (a higher conductor temperature >20°C would result in a higher observed resistance, Rt) 2. Incorrect length of cable (a longer length of cable would result in a higher observed resistance, Rt) Otherwise, there may be a case of: 3. Insufficient conductor purity (e.g. where the copper is less than 99.9% pure) 4. Insufficient conductor quantity (e.g. thinner or shortage of strands of wires resulting in a smaller conductor cross-sectional area) At Keystone Cable, the CR test is a routine test we conduct on every finished cable to ensure that the results comply with international specifications. For more enquiries, please contact our team. Contact Us The conductor resistance (CR) test is basic, but one of the most important tests in quality testing of cables. It can verify whether the amount or quality of conductor material in a cable is sufficient. The CR test is done on either a complete length of cable or on a cable sample of at least 1m in length in accordance with IEC 60228. The test measures the DC resistance of the copper or aluminium conductor, which indicates how easily current can flow through the conductor; the higher the resistance, the less current flow. When the resistance is too high, the heat generated may cause premature insulation failure, resulting in a fire or short circuit.   CR is influenced by the conductor dimensions, construction, temperature, and resistivity. Out of these factors, it is worth highlighting that because of the sensitivity of the reading to temperature, it is important to keep the sample in the test area for sufficient time to ensure that the conductor temperature has stabilized, which allows for an accurate test. The measured resistance is then converted to an equivalent resistance at standard temperature — 20°C according to IEC 60228 — and length. To ensure that the conductor resistance meets the standard, the observed resistance Rt is compared against the maximum conductor resistance at 20°C (R20) where:   Rt = Observed Resistancekt = Temperature Correction Factor (Table 1)L = Length of the specimen in mR20 = Maximum Standard Resistance at 20°C (Table 2) If you come across a high conductor resistance reading (> R20), here are possible calculation adjustment factors to first consider before exploring actual conductor issues:  1. Incorrect conductor temperature (a higher conductor temperature >20°C would result in a higher observed resistance, Rt) 2. Incorrect length of cable (a longer length of cable would result in a higher observed resistance, Rt) Otherwise, there may be a case of: 3. Insufficient conductor purity (e.g. where the copper is less than 99.9% pure) 4. Insufficient conductor quantity (e.g. thinner or shortage of strands of wires resulting in a smaller conductor cross-sectional area) At Keystone Cable, the CR test is a routine test we conduct on every finished cable to ensure that the results comply with international specifications. For more enquiries, please contact our team. Contact Us