Maximum Demand

Not all electrical loads in an installation operate simultaneously. A building with a 100 kW total connected load might only ever draw 60 kW at any one time because lighting, heating, and socket outlets are used at different times and never all at once. Maximum demand assessment estimates the realistic peak load by applying diversity factors to each circuit type. For domestic installations, standards like BS 7671 Table 1A provide specific allowances — the first 10A of lighting at 66%, cooking appliances with progressive reduction, and socket outlets with significant diversity. For commercial and industrial installations, demand factors depend on building use, occupancy patterns, and load characteristics. After-diversity maximum demand (ADMD) is commonly used for multi-dwelling developments. Accurate assessment avoids two expensive errors: undersizing, which causes overloading and nuisance tripping, or oversizing, which wastes capital on unnecessarily large cables, switchboards, and transformers. Load monitoring of similar existing installations provides the most reliable data for new designs.