[kmills25jhu]

I am trying to understand how you calculate electric load requirements for commercial properties - how do I know if 120/208 or 277/480 is right and how do I convert needs for one service into another?

[stanfortyman]

Your electrical contractor or EE should be able to tell you. This is nothing the customer should be concerned with from a construction standpoint, and is VERY far away from DIY work.

The actual answer is a to do a load calculation.

[KISS]

In somewhat simpler terms, a building with a large number or high HP motors for HVAC will inevitably mean 277/480. 277 will be used for lighting. 480 for the motor loads.

208/120 will of/course be necessary for other loads. e.g 208 for a small machine shop on property

Transformers convert the voltages. Higher voltages mean less current, which means less copper, which means less cost.

[jpen455]

Good response. Large loads do tend to indicate that the customer should use higher voltage, reducing amperage which reduces the size of the conductors (wires) and costs less. A transformer will convert (step down) the higher voltage (480/277v).