Where a delta bank of three transformers is installed to serve a load that is comprised mostly of 120-volt loads, all three transformers must be the same size.

• A. True
• B. False
• C. Depends on the load
• D. Not specified

Answer: (B)

In a delta-connected bank of three transformers, nothing forces all three units to be the same size. Each transformer is connected between two lines, and the current it carries depends on how the load is distributed across the three line pairs. If the loads are unbalanced or you’re delivering a lot of 120 V loads from particular line pairs, you can select different VA ratings for the transformers to match that specific demand. The important point is delivering the required three-phase voltages and total kVA while properly coordinating protection and impedance; identical sizing is not a strict requirement.

So, it isn’t necessary for all three transformers to be the same size; that’s why the statement is false.