What are the steps involved in cable sizing?



The major steps involved in the process of cable sizing are

1.Gather Data about the cable,its installation conditions,the load that it will carry.

Load Data-

Number of phases - Single phase or three phase.

Voltage - Rated voltage,allowed voltage

Full load current (A) or power

Full load power factor

Length of line- From source to load.This length should be as close as possible to the actual route of the cable and include enogh contigency for the vertical drops/rises and termination of the cable tails.

Basic Cable Data

Type of conductor material - Cu or Al

Insulation of the cable - PVC,XLPE,EPR (IEC cables)
TW,THHW,XHH (NEC cables)

Number of cores - 1X,2X … or 3G,4G …

Cable Installation

Installation Methods- cable tray/ladder,in conduit / raceways,on a wall,in air,directly etc
Environmental condition - Ambient or soil temperature at the installation site.

Cable grouping-Number of other cables bunched together or installed in the same area.

Cable spacing - whether cables are installed touching or spaced.

Soil thermal resisitivity - For underground cable

2.Determine the minimum cable size based on current rating

3.Determine the minimum cable size based on voltage drop.

4.Determine the minimum cable size based on inrush current.

5.Determine the minimum cable size based on short circuit temperature rise.

6.Select the cable based on the largest of the sizes calculated in the steps above.