AC Cable Size & Voltage Drop Calculation. Sizing of ac cable.

Hello everyone, this video is about calculating the size of ac cable for your application.
I have explained it with an example. After watching this video you will be able to calculate cable size and voltage drop for your project or application.

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Cable Sizing
1) Factors affecting the current carrying capacity of the cable.
a. Temperature
b. Cable laying
i. Induct
ii. In-ground: depth and thermal resistance of the soil.
iii. In open-air
c. Distance between the cables
d. Cable grouping factor

2) Calculate the full load current of your system
I = (Power in W)/3 x Voltage x Cos) for 3 phase
3) Calculate the correction factor K.
a. Depending upon your laying consideration whether it be underground or in open air or duct, select the correction factor from the cable datasheet.
b. Consider temperature factor for air or ground as per your application.
c. Consider the grouping factor if there are any existing cables or you have more number of runs of cable for this application.
d. Consider cable distance factor, generally speaking, consider 130mm to 200mm distance in between 2 cables. Refer datasheet for more details.
e. Soil resistivity factor if you are laying underground
4) Divide your full load current by K.
5) Find the cable that can provide current equal to or above the current value calculated at step 4.
6) Check voltage drop for that cable by formula,
Voltage Drop of Cable = (1.732x Current x (R cos +j sin) x Cable Lengthx100) / (Line Voltage x No of Runx1000)
Note: If mV/amp/m value is given on datasheet of cable then simply multiply that factor to your full load current and cable length to get voltage drop.

If the voltage drop is below permissible limit then ok, if not then increase run of cable or increase the size of cable depending upon which is economical.
7) Before finalization of cable,
Check this 2 things:
1. Cable Derating Amp should be higher than Full Load Current of Load.
2. Cable Short Circuit Capacity should be higher than System S.C Capacity at that Point.
This you need to calculate fault current or you can get refer to existing cable rating or breaker short ckt current rating.



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