Typically when you need to know this information you're dealing with an industrial building where power is critical due to the use of machines or in an area that will house servers for a large computer network.
Go to the main power distribution panel / breaker box, in most industrial buildings it will be in the warehouse, there will be a placard with that information stated clearly on it, you need to find the main panel however, the sub panels will be labeled as well and a common mistake of new or inexperienced commercial agents is to combine or select the wrong panel.
Understanding voltage and wiring configuration and the phase is important as well. Have an electrician walk you through the process once so you fully understand.
May 17, 2012