# How do you calculate the required transformer capacity (in kVA) rating for a 3 phase transformer?

**Issue:**

Calculation of kVA capacity for a Three Phase Transformer, based on Winding Voltage and Amperage information.

**Product Line:**

Low Voltage (LV) Transformers

**Environment:**

Applies to all Three Phase Transformers.

**Cause:**

kVA sizing must often be calculated from Primary or Secondary Winding Voltage and Amperage information.

**Resolution:**

To do this you must have at least two pieces of information:

- the load line-to-line voltage (
**V**) - the maximum load phase current (
**I**)

**kVA = (V * I * 1.732) / 1000**

where 1.732 is the simple numerical value for the square root of 3 (1.7320508...)

Then round up to the next standard 3ph kVA rating as found in Section 14 of SquareD/Schneider Electric Catalog, Digest 176.

**Example:** V = 208, I = 175; this calculates to 63+ kVA, thus we round up to 75kVA. From the Digest, a EE75T3H will satisfactorily serve this load.

**Note:** This is a simple kVA calculation and does not take into account possible special load requirements, such as found with motors or some medical equipment. For assistance, contact Product Marketing for support.

**Example:** For this, V = 208 (the load line-to-line voltage); I = 175 (175 amps per phase conductor)

kVA = (208 * 175 1.732) / 1000 = 63..05kVA Thus, round up to a 75kVA transformer. In this example, an EE75T3H.