Every building needs electricity, and getting the right amount of power into the right places is a sizing problem that architects must understand. This topic covers how electrical service enters a building, how power gets distributed from the main switchgear down through panels to individual circuits, and the critical decisions about transformer sizing and voltage selection that shape the entire distribution system.

The process starts with load calculations: adding up every connected load in the building, applying demand factors to account for the reality that not everything runs simultaneously, and then sizing equipment to handle that calculated demand plus room for future growth. The NEC (NFPA 70) governs the rules, but the architect needs to understand the sizing logic because electrical rooms, transformer vaults, and panel locations directly affect floor plans, structural loads, and coordination with other building systems.

Voltage selection drives the entire distribution strategy. Smaller buildings might receive 120/208V single-phase service directly from the utility. Larger commercial buildings typically receive medium-voltage primary service (often 13.2 kV or 4.16 kV) that gets stepped down through transformers to 480/277V for distribution, then further reduced to 208/120V at branch panels. The choice between these systems affects equipment size, conductor sizing, and ultimately the space you need to allocate for electrical infrastructure.

On the ARE, this objective tests your ability to apply standard sizing procedures to project scenarios. You need to understand how load calculations drive equipment selection, when different voltage levels are appropriate, and how spare capacity requirements affect system planning.