How to calculate amps in a three phase circuit

Written by james wiley
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How to calculate amps in a three phase circuit
(transformers 2 image by Kate Jones from

When dealing with large and powerful electrical equipment such as transformers, it is important to be able to accurately calculate the amps of the circuit or circuits involved, so that proper tools are used to operate the devices. The two most common types of transformers circuits are one phase and three phase amps. Calculating the amount of three phase amps requires knowledge of the total transformer size (kVA capacity of the circuit), as well as the line to line voltage. Transformers typically have their line to line voltage posted and sizes posted, and if they are not appropriately labelled contact the local electric company, who will have access to such information.

Skill level:
Moderately Easy

Things you need

  • Calculator

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  1. 1

    Multiply the total kVA by 1,000. It is important to note that if the transformer is labelled as 3- 100 kVA, the total kVA is 300 (3 x 100), since you are dealing with a three phase circuit.

  2. 2

    Multiply the line to line voltage by the constant of 1.732.

  3. 3

    Divide the number computed in Step 1 by the number calculated in Step 2. The resulting number will be the total amps in the three phase circuit. The formula for a 3- 100 kVA 240 volt transformer would look like this: 300 x 1,000/ 1.732 x 240= 721.71 amps

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