Cable selection

LSZH Flame Retardant (FRT) and LSZH Fire Resistant (FR) cable are two distinct types of cable properties, although these terms are often misused. Flame and Fire can be used interchangeably, but confusion occurs between Retardant and Resistant. Knowing what these cable properties mean can help ensure you get the suitable cable for your application. LSZH Flame Retardant (FRT) Cable LSZH FRT cable is a cable that does not promote the spread of fire. But the cable will not maintain circuit integrity in the presence of fire. The international standards on flame propagation are IEC 60332-1-2 for a single insulated wire or cable or IEC 60332-3 for vertically mounted bunched wires or cables under fire conditions.  To ensure safety during a fire, FRT cable typically uses LSZH material. LSZH produces little smoke or acidic gas when burned**, so LSZH FRT cable also undergoes acid gas emission tests to IEC 60754 or BS EN 60754 and smoke emission tests to IEC 61034 or BS EN 61034.  LSZH FRT cable is a vital cable to be used in enclosed areas with high foot traffic, such as underground passenger systems, airports, schools, hotels, hospitals, and high-rise buildings.  LSZH Fire Resistant (FR) Cable LSZH FR cable is a fire safety product, which means it not only reduces the spread of fire, it will maintain circuit integrity in the presence of fire. FR cable has a layer of mica tape around individual copper conductors. Mica is an incombustible natural inorganic mineral with high dielectric strength and excellent heat resistance. Hence during a fire, the mica acts as a fire barrier to the conductor and maintains circuit integrity. In addition to LSZH FRT tests (IEC 60332, IEC 60754, and IEC 61034), LSZH FR cable is also tested to SS 299, SS299-1, BS 6387, IEC 60331. These tests cover the cable’s resistance to fire, resistance to fire with water and resistance to fire with mechanical shock. LSZH FR cable is an important cable to be used when you require critical electrical installations to perform during a fire evacuation: fire alarm systems, voice alarm systems, and emergency lighting systems. At Keystone, we ensure that our LSZH FR cables fulfil BS 6387 Cat. CWZ provides the highest performance and safety levels for such cables. **What is Low Smoke Zero Halogen (LSZH)?  To understand the properties of LSZH, we compare it to the most commonly used cable material, PVC or polyvinyl chloride. In the event of a fire where PVC burns, black carbon smoke and hydrogen chloride gas (HCl) are released. Black smoke impedes general vision. And when gaseous hydrogen chloride comes in contact with moisture, such as a person’s eyes, mouth, throat and nose, it dissolves to form hydrochloric acid, causing extreme irritation and choking, hindering escape. (CH2CHCl)n + O2 → CO2 + CO + HCl + H2O LSZH, because of inorganic additives such as aluminium hydroxide or magnesium hydroxide, releases gaseous water when burned, which helps envelop the flame and exclude oxygen from the fire. In this chemical reaction, the decomposed products are non-toxic and the mineral phases MgO and Al2O3 are alkaline, reducing the likelihood of acidic gas irritations. When burned, LSZH also emits less optically dense smoke, thus allowing better vision and escape.  Mg(OH)2 → MgO + H2O or 2Al(OH)3 → Al2O3 + 3H2O For more information on LSZH cables, please get in touch with our sales team.

In our line of work, we get many good questions on suitable cable sizes. We have distilled here some of the key considerations we recommend looking into to determine the suitable cable size.  This article primarily references low-voltage power cables with copper conductors. *TIP: To keep the information handy, we also recommend reaching out to our sales team, who will take you through a step-by-step cable sizing example using Current-Carrying Capacity Method, Voltage Drop Method and how to apply the correction factors described in this article. The guide includes a comprehensive list of cable sizing tables for your calculation references.  The guiding principle in choosing the right cable size is how well your cable can carry the required current load in your installation environment without causing excessive voltage drop from your supply voltage. Once you know the load the cable will carry (Ampere), here are some conditions that would affect the ultimate cable size you choose. Going through the considerations below may bring you to different recommended conductor sizes. The key is that the minimum conductor size you select must at least be the minimum allowable cable size that can cover all the conditions you have looked into. With that in mind, here are five questions we would typically ask: 1. Installation Method This is the first thing we look at because how and where the cable will be installed directly affects whether a cable could be overloaded (e.g. in conduit, on cable tray, in free air, grouping, spacing, trefoil, laid flat). Generally, the more enclosed the cables are (e.g. in conduit versus. in free air), the more you may need to use a larger cable size to ensure it can withstand the current and allow proper heat dissipation. 2. Cable Material  Cable insulation material (the extruded layer after the conductor) is important in cable sizing because it directly affects your cable’s maximum operating temperature. For your reference, we have placed common insulation materials: PVC, XLPE, and EPR in the guide.  In standard cable materials, PVC has a maximum operating temperature of 70˚C, XLPE 90 ˚C and EPR 90 ˚C. You may wonder why, for instance, we would choose PVC vs XLPE, given the lower maximum operating temperature for PVC. This relates to other material properties that work better in your installation environment. For instance, PVC is much more flexible than XLPE and may be a better choice where you would require the cable to bend in tighter spaces.  You may also choose between single-core or multi-core cables depending on the installation requirement, which would also affect the current carrying capacity of the cable. A single-core cable would be able to dissipate heat better than a multi-core cable and hence would have a higher current carrying capacity. However, you may still choose the multi-core cable as installing the required conductors at go could be easier. 3. Cable Length We require cable length to assess Voltage Drop, which is the loss of electrical potential along your cable run. In Singapore, we follow the SS638 (formerly known as CP5) wiring regulations, where the voltage drop of a cable run must not exceed 4%. For instance, if a supply voltage is 415V, then the maximum permissible voltage drop cannot exceed 4% of 415V = 16.6V The cable size and length of a cable line mainly determine the voltage drop of a circuit. The smaller the cable size or, the longer the cable length required for your circuit, the greater the voltage loss. If you find that the voltage drop of the circuit has exceeded the 4% stated, you would need to upsize your cable. 4. Ambient Temperature Our tables assume a standard ambient temperature of 30˚C in free air or a ground temperature of 15˚C with a depth of 0.5m. Do note that cable routing and ventilation will directly affect your ambient temperature, so it is important to consider the installation condition along the entire length of the cable laid. If there is a deviation from the standard temperature, you must apply a correction factor to the current load your cable is expected to carry. The higher your ambient temperature from the standard, the larger your cable size may be needed to carry the required load.  5. Number of circuits Our tables assume that you are laying one circuit single-phase or three-phase. If you intend to group circuits in your installation, it is crucial to apply a cable grouping correction factor so that you select the appropriate cable size that would prevent overheating issues. The more circuits you intend to group, the harder the heat dissipation; hence you may need to upsize the cables accordingly.  We hope this article has given you a general idea of some key factors to consider when determining the minimum allowable cable size. To reiterate, you may choose the minimum economic size to cover all the conditions you have looked into to ensure the cable does not get overloaded. To help with your cable size estimates, please refer to the free guide below, where we take you through a step-by-step example and include cable sizing tables for your calculations.  For more information, please contact us.