Your electric service to your building is sized to handle the electrical load required by the building. As needs change, equipment is added, building an addition, or equipment requires different voltages; changes or upgrades may be required.
The electric service to a building supplies all the power to the building. Standard voltages are 120/208 and 277/480 in our area. Both single phase and three phase are usually available but three phase is typically used for any commercial or industrial building. Sizing of the electrical service is dependent on the load served. Design of the service requires a list of all electrical loads planned for the building including lighting, HVAC systems, production machinery, and any other equipment in the building. Electrical code dictates how to calculate the required service size based on equipment loads and a demand factor which is a way to determine how long the load would be present on the service in any given time period. Power from the utility grid can be delivered to the building with either primary or secondary voltage. In the case of primary supply, the building would have a pad mounted transformer rated for the power company grid voltage. That voltage is transformed to the building service voltage and brought into the building service panels on secondary conductors from the transformer. in the case of secondary supply, the transformers would be installed by the power company on their poles, and secondary supply is brought into the building service panel at the service voltage. An electrical service sized larger than 400 amps is usually required to have a pad mount transformer and would normally be less expensive.