I want formula to calculate cable size as per load given in
kw & amp.I searched many sites but didn't right answer.Plz
reply me asap.

Answer Posted / engr. abed alraheem

dear you can calculate the size of the cable as follow:

first you need to measure the current capacity and it's low as follow:
Kw/(P.F * Voltage that we wanna use)= current

so when you get the current capacity for the load you can get the size from catalogs there is tables gives you the rating of current and how much the size for every rate for this current.

and this current will be ok if we dont have a voltage drop in line of distance between the source and the load.

actually all the distance between the load and the source have a voltage drop so we have to use this law in order to measure the percentage Voltage drop and it has be 2.5% from the load to panels:

V.D = {((x sin@ + Y cos @) x I x L)/ V } x 100%

I is the current that you measured.
L is the distance between the load and the panel.
V is the voltage that we use.
X is the AC resistance.
y is the AC reactance but sometime we ignore it.
X,Y it is depends on the size of cable so when you chose size this factors will control the voltage drop and you can change it sometimes to get the voltage drop rate as 2.5%

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