Split Phase Power Calculator

Split-phase power is the standard residential electrical service in North America, providing both 120 V (for general outlets and lighting) and 240 V (for large appliances) from a single-phase transformer secondary. The term 'split-phase' refers to the transformer secondary winding being center-tapped, creating two 120 V legs (L1 and L2) that are 180° out of phase with each other and a neutral at center potential.

The standard residential service panel receives three conductors from the utility transformer: L1 (120 V to neutral), L2 (120 V to neutral, 180° out of phase with L1), and a neutral (N). Between L1 and L2 the voltage is 240 V, used for electric dryers, ranges, water heaters, central air conditioners, and EV chargers. The neutral carries the difference current between L1 and L2 loads.

Understanding split-phase power is essential for residential electricians, homeowners planning circuit additions, and engineers sizing service entrance equipment. A 200 A split-phase service delivers a maximum of 200 A on each leg, for a total apparent power of 200 A × 240 V = 48 kVA. However, the actual usable power depends on the balance of loads across L1 and L2 and their power factors.

The neutral current is the vector difference of L1 and L2 currents. For balanced loading (equal currents on both legs), the neutral carries zero current — the ideal condition that minimizes neutral conductor heating and voltage imbalance. When loads are heavily unbalanced, the neutral must carry the full difference current, which is why the neutral conductor in residential wiring is sized the same as the line conductors.

For 240 V-only loads (water heaters, EV chargers), current flows from L1 through the load to L2 with no neutral connection. Both legs carry equal current, and neutral current is zero for that load. The power calculation for such loads uses the full 240 V: P = 240 × I × PF.

Load balancing across the two legs of a split-phase service is good electrical practice. Panel manufacturers typically alternate circuit breaker positions to encourage balanced loading, but the final distribution depends on which circuits are loaded simultaneously. Electricians use a clamp meter to measure L1 and L2 currents at the panel and rearrange circuits if imbalance exceeds 10%.