How do you find cable size with given kilowatts?

Answer 1

To select the proper cable size you need to know all of the following:

circuit ampacity needed

ambient temperature

length of circuit from point 1 to point 300

number of conductors in the raceway or cable

type of insulation being used

voltage: whether above or below 380 volts

and for some pieces of equipment, the manufacturer's instructions.

Answer 2

If you know the kilowatt rating of the load you need to either know the supply voltage or the impedance of the load in order to find out the amperage required, which is what dictates the size of conductor needed. It is more likely you would know what the supply voltage is (likely 120 or 240 Volts).

To find amperage use the formula:

I = P/E

where I is Amperage, P is power in watts, and E is voltage

Example:

1200 Watt load on a 120 Volt line

I = 1200/120

=10 Amps

When you know the required amperage you need to look at the type of wire needed. IE inside your home, in a wet location, in an attic etc. (in the Canadian Electrical Code this is table 19)

Once you have selected a wire type then you can select a wire (in the Canadian Electrical Code this is table 2)

Answer 3

If you are asking how do you determine an appropriate cable to supply a given load in kilowatts, then you need to know the supply voltage in order to determine the current drawn by the load. You then need to check the appropriate cable tables (in your electrical code book) -but you will also need to know the number of cores, the type of conductor, the type of insulation, how it is to be installed, etc., as well as the load current.