How to select Electrical power cable sizing?

The cables in electrical systems are used to transport electrical currents. The core of these cables is usually made of copper or aluminum in order to conduct current with minimal voltage drop. The majority of cables have protective insulation that protects both the cable and living beings from dangerous voltages. If the cables are different types, they are divided into the following categories:

  • Current goes through (cable size)
  • Purpose they are used
  • Place (indoor or outdoor)
  • Protection level required

Selection criteria for Cables:

Voltage drops:

A voltage drop is a decrease in voltage in an electrical circuit between a source and a load. When a cable is selected to receive the current for a particular machine, IEEE regulations require that the cable voltage drop be less than 4% of its rated supply.

All successive drops must be included in the total voltage drop. The maximum permissible voltage drop of the cable must be 4%. Factors affecting the voltage drop are:

Cable’s Resistance for 1m length (Voltage drop for 1m- [v/Am]) - Vc

I- Rated current of the cable (or carrying current)

L- Length of the cable

So Vd(Voltage drop of the cable) can be calculated as,

Vd= ILVc

Derating Factors:

In standard conditions, all cables on the market are marked with a current that they can carry. However, in a construction, these standard conditions cannot always be maintained. There may be current variations if a cable is chosen based on the (current) requirements according to our assembly method. Power reduction factors are factors that influence previous variations. They are, indeed.

  • Ambient temperature
  • Ground temperature
  • Depth of lying
  • Soil Thermal resistivity

Current ratings of cables:

The classification of electric wires differs from manufacturers; however, they are almost similar. The approximate current ratings for wire sizes are shown below

Calculating the Cable for a given load:

For calculating the proper cable, we have to know the power consumption Known input voltage. And also, the distance between the power supply and load (L) is provided.

Then steps include:

  • Determine the load current using the information provided.
  • Then multiply the selected wire’s rated current by all of the derating factors.
  • Determine whether or not Iwire x derating factors I
  • If this is the case, choose the next larger wire size. If not, choose that wire.
  • Next, calculate the wire voltage drop and the nominal voltage drop to see if everything is in order.