Electrical demand and feeder sizing for PE Architectural Engineering

Begin with the system, not the arithmetic

Identify whether the load is single-phase or three-phase, the applicable line-to-line or line-to-neutral voltage, and whether the question asks for connected load, demand load, current, or equipment rating.

Demand factors, continuous-load treatment, efficiency, and power factor serve different purposes. Apply only the factors supported by the stated condition and controlling reference.

Reliable solution sequence

• Inventory loads and units before applying factors.
• Separate continuous and noncontinuous portions when required.
• Apply demand or diversity rules only to eligible load categories.
• Convert power to current with the correct phase and voltage relationship.
• Check conductor, overcurrent protection, equipment, and coordination implications separately.

Common failure modes

Frequent errors include using line-to-line voltage for a line-to-neutral load, applying the square-root-of-three factor to a single-phase circuit, confusing demand with power factor, or applying a demand factor twice after it is already reflected in the stated load.