Final answer:
Commercial installations are commonly provided with three-phase electrical service to handle large power loads. Economies of scale make it more efficient for a single company to supply this service to avoid duplicative investments.
Step-by-step explanation:
Commercial installations are typically supplied with three-phase service. This is due to the demands of commercial enterprises, which often require higher power loads for equipment such as HVAC systems, computers, and machinery. In addressing economies of scale, commercial entities tend to be served more effectively by a single power company. The installation of infrastructure by one entity reduces the marginal cost and prevents costly duplication of services that would occur if multiple companies provided the same utility to an area.