Cable Size

4295 WordsAug 15, 201318 Pages
Cable Sizing Calculation From Open Electrical Jump to: navigation, search Contents[hide] * 1 Introduction * 1.1 Why do the calculation? * 1.2 When to do the calculation? * 2 General Methodology * 2.1 Step 1: Data Gathering * 2.1.1 Load Details * 2.1.2 Cable Construction * 2.1.3 Installation Conditions * 2.2 Step 2: Cable Selection Based on Current Rating * 2.2.1 Base Current Ratings * 2.2.2 Installed Current Ratings * 2.2.3 Cable Selection and Coordination with Protective Devices * 2.2.3.1 Feeders * 2.2.3.2 Motors * 2.3 Step 3: Voltage Drop * 2.3.1 Cable Impedances * 2.3.2 Calculating Voltage Drop * 2.3.3…show more content…
The component parts that make up the cable (e.g. conductors, insulation, bedding, sheath, armour, etc) must be capable of withstanding the temperature rise and heat emanating from the cable. The current carrying capacity of a cable is the maximum current that can flow continuously through a cable without damaging the cable's insulation and other components (e.g. bedding, sheath, etc). It is sometimes also referred to as the continuous current rating or ampacity of a cable. Cables with larger conductor cross-sectional areas (i.e. more copper or aluminium) have lower resistive losses and are able to dissipate the heat better than smaller cables. Therefore a 16 mm2 cable will have a higher current carrying capacity than a 4 mm2 cable. Base Current Ratings Table 1. Example of base current rating table (Excerpt from IEC 60364-5-52) International standards and manufacturers of cables will quote base current ratings of different types of cables in tables such as the one shown on the right. Each of these tables pertain to a specific type of cable construction (e.g. copper conductor, PVC insulated, 0.6/1kV voltage grade, etc) and a base set of installation conditions (e.g. ambient temperature, installation method, etc). It is important to note that the current ratings are only valid for the quoted types of cables and base installation conditions. In the absence of any guidance, the following reference based current ratings may be
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