Enter the CT ratio and the secondary current (amps) into the calculator to determine the Primary Current From CT Ratio. 

Primary Current From CT Ratio Formula

The following formula is used to calculate the Primary Current From CT Ratio. 

Ip = CT * Is

  • Where Ip is the Primary Current From CT Ratio (amps)
  • CT is the CT ratio 
  • Is is the secondary current (amps) 

How to Calculate Primary Current From CT Ratio?

The following two example problems outline how to calculate the Primary Current From CT Ratio.

Example Problem #1:

  1. First, determine the CT ratio. In this example, the CT ratio is measured to be 40.
  2. Next, determine the secondary current (amps). For this problem, the secondary current (amps) is calculated to be 5.
  3. Finally, calculate the Primary Current From CT Ratio using the formula above: 

Ip = CT * Is

Inserting the values from above and solving the equation with the imputed values gives: 

Ip = 40 * 5 = 200 (amps)


Example Problem #2: 

Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:

CT ratio = 60

secondary current (amps) = 3

Entering these values into the formula or calculator above gives us:: 

Ip = 60* 3 = 180 (amps)