3 Phase Motor Cable Size Calculator

If we make the connection of electricity, then one thing comes to mind that how many mm2 of cable will have to be used to connect the meter to the pole. To answer this, first, the rating of the cable depends on how many kW of load the connection will be connected to the meter. That is, the size of the cable depends on how many kw of sanction load / connected load / maximum demand. If the connection is of domestic mode or commercial mode and the load is 5 kw then a single phase 2 core PVC cable will be used and if the connection is in 3 phase motor or industrial mode then 3 or 4 core 3 phase PVC cable will be used. This 3 phase motor cable size calculator can be used for calculating PVC cable size for connecting motor (kw/ hp) to supply point.

What is PVC cable –

The full form of PVC is Polyvinyl Chloride and as we know that PVC is a thermoplastic polymer chemical material, the polymeric property of PVC provides stability to the cable at high and low temperatures and the insulation of the cable is the same in both cases. remains the same. The polymeric property of PVC helps prevent degradation where protection against UV light is required. Apart from this, the main property that makes this PVC cable unique is the PVC insulation. PVC cable is used primarily on locations that require minimum corona effect resistance, and low and medium-voltage motor or electrical equipment, and low-frequency insulation. PVC Cable is available at low cost and also has excellent aging properties and this cable can be easily used for 25 to 30 years.

How to Calculate Cable Size in sq mm Formula for motor-

In the case of LV/ low voltage system or load, the cable size and rating can be selected based on its current carrying capacity and the voltage drop across the cable length but in the case of the Medium and high voltage system, the cable short circuit capacity is an important and final factor. That is, in the case of the HT motor, the short circuit current capacity of the cable plays a major role in determining the size of the cable. So in the case of HT motor, cable short circuit current capability solely is sufficient to finalize the cable size, as the other two parameters will be adjusted automatically.

Cable Size Calculation of 90 Kw LT Motor

Motor KW = 90 kw 

Pf = 0.8, Efficiency = 94%

System Voltage, V1 = 415

Cable length = 100 m

P = √3 x V x I Cos Φ for 3 phase load 

P = V x I Cos Φ for 1 phase load 

Rated Load Current = P / (1.732 x V x Pf x Eff) 

I= 90000 / (1.732 x 415 x 0.8 x .99 )

=90000/540= 157 amp

~ 157 A

in ideal case 157 amp shall be current capacity of cable and if we look at the cable size chart we will find that for 157 amp the current rating cable size 70mm2 cable size would be perfect. 

But, The rating of the PVC cable also depends on many other factors, which increase the current rating capacity of the cable and derate the cable. the factor which affects or lower the rating of cable from the ideal case are as follow-

  1. Variation In Ambient Air Temperature
  2. Depth Of Laying For Cables Laid Direct In The Ground 
  3. Ground Temperature For Cables In Ducts

In the case of copper wire PVC cable derating factor due to the above three causes would be 1.30.

So actual current rating shall be- 1.30x 157 amp= 205 amp

Now in actual if we look at the chart given below then a 95 mm2 PVC cable would be perfect to use for connecting the motor to the supply point.

Cable size chart for motor –

If we calculate the current capacity of the motor or get the current capacity from the name plate of the motor, then through the cable size chart given below, we can get the size of the cable (mm2). by using the above 3 phase motor cable size calculator we can also get cable size without calculation.

PVC size Cross Section area  (mm2)Approximate cable Overall Diameter (mm)Current Rating of cable For single Phase (Amps) Current Rating of cable   For Three Phase (Amps)

kW to cable size chart-

If we have available kw / hp rating of motor or maximum load /sanction load of domestic (light fan connection) then in such case how many mm2 of cable should be used from pole to meter, cab be got through the chart given below. by using 3 phase motor cable size calculator we can also get cable size without calculation.

HPkWAmpsCable Size (AL)Cable Size (Cu)

9 thoughts on “3 Phase Motor Cable Size Calculator”

  1. Excellent work. Solves lengthy calculations in seconds. I found it practictically feasible. Enough for engineers and technicians deployed on installation work.

  2. Thanks for sharing your experience, I just wanted to know why the cable length is not considered in the motor cable size calculator and how the type of motor starter (i.e. DOL or VFD) can affect it as well. Thanks


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