Calculates a single-family dwelling's electrical service demand load using either the NEC Article 220 Part III Standard Method (general lighting/small-appliance/laundry loads with Table 220.42 demand factors, fixed appliances per 220.53, range per Table 220.55, dryer per 220.54, and HVAC per 220.60) or the 220.82 Optional Method (all other loads summed at nameplate with a single 10kVA/40% demand step, HVAC handled separately), then recommends a minimum standard service size.
Standards followed
NEC 220.12 — general lighting load (3 VA/sq ft, dwelling occupancy)NEC 220.52 — small-appliance and laundry branch-circuit loadsNEC Table 220.42 — general lighting/small-appliance/laundry demand factorsNEC 220.53 — fixed-appliance demand factor (75% for 4 or more)NEC Table 220.55 — electric range demand loadNEC 220.54 — electric dryer demand loadNEC 220.60 — non-coincident (heating/cooling) loadsNEC 220.82 — Optional Method for a single dwelling unit
What it can do
- Standard Method: full Table 220.42 tiered demand factor, 220.53 fixed-appliance rule, simplified Table 220.55 range demand, 220.54 dryer minimum.
- Optional Method: single 10kVA/40% demand step per 220.82(B), with a user-selectable HVAC demand factor per 220.82(C) (100% A/C or heat pump; 65% electric heat, fewer than 4 units; 40% electric heat, 4 or more units).
- EV charger load included per NEC 220.57 at 7200 VA or the nameplate rating, whichever is larger.
- Recommended minimum standard service size from the computed demand amps.
Example problem
Standard Method: 2000 sq ft, 2 small-appliance circuits, 1 laundry circuit, 3 other fixed appliances totaling 4500VA, 10kW range, 5000VA dryer, 4800VA cooling / 10000VA heating, 240V, no EV.
- General loads = 6000+3000+1500 = 10,500 VA → demand = 3000 + (10500−3000)×0.35 = 5625 VA
- Fixed appliances (only 3, under 4) = 4500 VA at 100%
- Range ≤12kW → 8000 VA (Table 220.55). Dryer = max(5000, 5000) = 5000 VA. HVAC = max(4800, 10000) = 10,000 VA
- Total = 5625+4500+8000+5000+10000 = 33,125 VA → 33125/240 ≈ 138.0A → 150A recommended service
≈138.0A demand, 150A recommended minimum service.
This targets the common single-family-dwelling case and simplifies several Article 220 edge cases: it assumes a single range and single dryer, doesn't auto-detect the heat-pump/electric-heat 220.82(C) branch (you select the applicable demand factor directly), and doesn't cover multi-family or mixed-occupancy calculations. Always verify against the full Article 220 text and the code edition adopted by the AHJ for a final service size.