NEC 220 Residential Service Load Calculator
Deterministic 120/240V single-phase electrical service load calculation per NEC Article 220.82. Computes general lighting (3 VA/sq ft), small appliance branch circuits, continuous EV supply equipment (125% per NEC 625), HVAC heat pump auxiliary strips, and NEC Table 310.16 75°C service conductor gauges.
NEC Calculation Principles & Statutory Code
1. NEC 220.82(B) General Loads Demand Factor
The optional method combines general lighting (3 VA/sq ft), small appliance circuits (1,500 VA each, min 3), and nameplate ratings of cooking, laundry, and water heating appliances. The first 10,000 VA is assessed at 100%; all remaining load is derated to 40% based on empirical residential non-coincidence factors.
2. Continuous Duty Loads (NEC 625 & 210.20)
Electric vehicle supply equipment (EVSE) draws maximum rated current for 3 or more continuous hours. Under NEC 625.42 and 210.20, branch circuits and feeder sizing must apply a 125% continuous duty multiplier (a 40A EVSE is calculated at 50A / 12,000 VA).
3. HVAC Interlock & Auxiliary Heat (NEC 220.82(C))
For central heat pumps with supplemental electric strip heat, compressor rated load current (RLA) is assessed at 100%, and supplemental electric resistance heating is assessed at 65% demand factor under NEC 220.82(C)(3) when the compressor and strips operate concurrently.
4. Service Conductor Table 310.16 (75°C Ampacity)
• 150A: #1 AWG Cu / 2/0 AWG Al
• 200A: 2/0 AWG Cu / 4/0 AWG Al
• 300A: 350 kcmil Cu / 500 kcmil Al
• 400A: Parallel 3/0 AWG Cu / Parallel 250 kcmil Al