FAQ Search

How do you calculate the required transformer capacity (in kVA) rating for a 3 phase transformer? Example: 3ph 480 delta to 208Y/120, 175 amps of simple lighting load

To do this you must have at least two pieces of information:  1) the load line-to-line voltage (V), and 2) 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 the Digest 172.

Example:  V = 208, I = 175; this calculates to 63+ kVA, thus we round up to 75kVA.  From the Digest, a 75T3H 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, a 75T3H.


CTA-ID : 2006359
FA101694  |  25-Jun-2012  | Selection
  • Please rate the content of this information
    Unhelpful 1 2 3 4 5 Helpful