How to Determine the Proper Cable & Wire Size for a Given Load?īelow are solved examples demonstrating how to find the proper cable size for a given load.įor a given load, cable size may be determined using various IEC and NEC tables (such Article 310 – Table – 310.15 (B) 16. How to Determine the Suitable Size of Inverter for Home Appliances?.How to Size a Generator? Portable, Backup & Standby for Home & Commercial Applications.If the calculated value of voltage drop is greater than the value calculated in step (1) (Maximum allowable voltage drop), than calculate voltage drop for the next (greater in size) cable and so on until the calculated value of voltage drop became less than the maximum allowable voltage drop calculated in step (1).If the calculated value of voltage drop is less than the value calculated in step (1) (Maximum allowable voltage drop), than the size of selected cable is proper.This is the value of Volt drop in the cables when load current flows through it.Load factor = Load Current to be taken by Cable/ Rated Current of Cable given in the table. Now multiply this calculated value of volt drop by load factor where.(Actual length of circuit x volt drop for 100ft) /100 => to find volt drop in 100 feet. (Actual length of circuit x volt drop for 1m) /100 => to find Volt drop in per meter. Now, calculate the voltage drop for the actual length of the wiring circuit according to its rated current with the help of following formulas.(Stay cool :) We will follow both methods and systems for finding voltage drops (in meters and 100 feet) in our solved example for whole electrical installation wiring). From Table 1, find the voltage drop in meter or 100 feet (what system you prefer) according its rated current.Now, according to the load current, select a proper cable (which current rating should be nearest to the calculated load current) from table 1. First of all, find the maximum allowable voltage drop.To find voltage drop in a cable, follow the simple steps given below. what would be the voltage drop in a one meter cable which caries one Ampere current? Normally, Voltage drop in tables is described in Ampere per meter (A/m) e.g. In electrical wiring circuits, voltage drops also occur from the distribution board to the different sub circuit and final sub circuits, but for sub circuits and final sub circuits, the value of voltage drop should be half of that allowable voltage drops (i.e. Refer to the NEC Code – 310-16 which stats 20% of additional ampacity for every 100 feet of distance should be added to counter the voltage drop in the circuit. Similarly, if the supply voltage is 120V AC, the allowable voltage drop should be no more than 3V for separate branch circuit (120V x 2.5%) and 5% for feeder and branch circuits (120V x 5%). If the supply voltage is 230V AC, then the value of allowable voltage drop should be
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