Electrical Panel Schedule Calculator

Article 220 of NFPA 70 (the National Electrical Code) assumes lighting and receptacle circuits are rarely all drawing full current simultaneously once a building is large enough, so this calculator applies the standard first-10,000-VA-at-100%-then-50% discount to both Lighting load (VA) and Receptacle load (VA). HVAC load (VA) is treated as continuous, code-required capacity and counted at a full 100% with no discount, which is why a large HVAC load pushes Total demand (VA) up more directly than an equally large lighting or receptacle load.

No -- Total demand (VA) and Total connected (VA) are pure volt-ampere sums of the four load inputs and never reference Panel voltage (V) or Phases (1 or 3). Those two inputs only come into play when converting the demand load from VA into amperes (Demand load amps (A)), where three-phase divides by voltage times the square root of 3 instead of voltage alone.

This calculator selects the smallest bus rating from a standard table (100 A up to 2,000 A) and the smallest panel space count from another (12 up to 42 spaces). The flag reads 1 whenever EITHER table is exceeded, and the two cases are very different -- check Bus loading (%) to tell them apart. If Bus loading (%) is at or under 100%, only the panel space count exceeded its table: Min bus rating (A) is still a safe, real recommendation, and you likely just need more circuit spaces (e.g. a subpanel). If Bus loading (%) is over 100%, the bus itself is undersized: Min bus rating (A) is only the largest table entry shown for reference, not a safe recommendation, and you need a custom switchgear design from an electrical engineer instead.

Bus loading (%) is Adjusted amps (125%) divided by the selected Min bus rating (A). It normally stays at or under 100% because the calculator selects a bus rated at least as large as the adjusted load. If your combined loads are large enough that no standard bus size (up to 2,000 A) is big enough, the calculator falls back to the largest available size and Bus loading (%) can read over 100% -- check Exceeds Standard Sizing in that case, since the displayed bus rating is undersized for the actual load.