Calculate Amperage

When calculating the amperage on a branch circuit, you must know if it is a single or a three phase circuit. In case of a 3 phase circuit, you will have a constant multiplier that you'll need to use in the formula. Look at the examples below, and how the formula is used.

Calculating Amperage - 1 Phase

I (Amperage - also known as Current)

VA (Volt Amp - also known as Watt)

V (Volt)

Formula to Use:

I = VA / V

Example 1:

Find the Amperage of an 2400 VA load on a 120 Volt, 1 phase branch circuit.

Use the formula above, and substitute the given values.

I = 2400 / 120 = 20 Amps

Example 2:

Find the Amperage of an 5600 VA load on a 240 Volt, 1 phase branch circuit.

Use the formula above, and substitute the given values.

I = 5600 / 240 = 23.34 Amps

Calculating Amperage - 3 Phase

I (Amperage - also known as Current)

VA (Volt Amp - also known as Watt)

V (Volt)

1.732 (Multiplying Factor to use for 3 Phase circuits; Sometimes this is represented as the square root of 3)

Formula to Use:

I = VA / (V * 1.732)

Find the Amperage of an 2400 VA load on a 240 Volt, 3 phase branch circuit.

Use the formula above, and substitute the given values.

I = 2400 / (240 * 1.732) = 5.78 Amps

Example 2:

Find the Amperage of an 7600 VA load on a 480 Volt, 3 phase branch circuit.

Use the formula above, and substitute the given values.

I = 7600 / (480 * 1.732) = 9.15 Amps

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