Commercial and Industrial Calculations

James G. Stallcup

Commercial and industrial facilities such as offices, banks, stores, restaurants, welding shops, and refineries have diverse electrical loads. These loads are considered to be either continuous or noncontinuous, and demand factors, under certain specified conditions, are permitted. Continuous load is defined in Article 100 of the National Electrical Code®, as any load “where the maximum current is expected to continue for 3 hours or more.” Demand factor is defined as the ratio of the maximum demand load to the total connected load, or simply put, a factor applied to a load that is less than 100 percent. Loads must be calculated based on the type of occupancy and the requirements of the equipment supplied. Either the standard or the optional calculation can be used to calculate the loads in volt-amps or amps to size a feeder and service conductors and associated distribution equipment. How the lighting, receptacle, and equipment loads are utilized in a specific occupancy determines how they are grouped and classified in order to apply the correct calculation requirement.