Residential Load Calculations
General lighting loads, demand factors, voltage drop calculations, the K-factor formula, and single-phase circuit sizing under the 2026 NEC.
- Calculate general lighting load at 2 VA per square foot for dwelling units per 2026 NEC
- Apply 2026 NEC Article 120 load calculation rules (relocated from Article 220)
- Use the voltage drop formula VD = 2 x K x I x D / CM
- State the 3% branch circuit and 5% total voltage drop recommendations
- Identify the K value for copper conductors in voltage drop calculations
Lección 1
General Lighting Load - 2 VA Per Square Foot (2026 NEC)
The Foundation of Residential Load Calculations
Every residential service sizing calculation starts with the general lighting load. Under the 2026 NEC, the unit load for dwelling units is 2 VA per square foot of floor area (reduced from 3 VA/sq ft in prior editions). This value covers general-purpose receptacles and lighting outlets throughout the home. The relevant code reference is now in Article 120 (load calculations relocated from Article 220 in the 2026 NEC).
Pre-2026 NEC (Article 220)
General lighting: 3 VA per sq ft
Load calculation: NEC Table 220.12
2026 NEC (Article 120)
General lighting: 2 VA per sq ft
Load calculation: NEC Article 120
Floor Area Calculation
The floor area is measured from the outside dimensions of the building and includes:
- All habitable space on every floor
- Finished basements and attic spaces adaptable for future use
- Unfinished areas that are wired
It does not include:
- Open porches
- Garages
- Unfinished, unwired spaces
Adding Required Circuit Loads
In addition to the general lighting load, the following must be included:
| Load | VA Value |
|---|---|
| General lighting | 2 VA x floor area (sq ft) - 2026 NEC |
| Each small appliance circuit (min 2) | 1,500 VA per circuit |
| Laundry circuit | 1,500 VA |
Example for a 2,000 square foot home under the 2026 NEC:
- General lighting: 2,000 x 2 = 4,000 VA
- Small appliance circuits (2): 2 x 1,500 = 3,000 VA
- Laundry circuit: 1,500 VA
- Subtotal: 8,500 VA
Exam Tip - Always Include All Three
When calculating the general lighting and receptacle load under the 2026 NEC, always add together: (1) the 2 VA/sq ft lighting load (Article 120), (2) the small appliance circuits at 1,500 VA each, and (3) the laundry circuit at 1,500 VA. Then apply demand factors to the total.
Per the 2026 NEC Article 120, the general lighting load for dwelling units is 2 VA per square foot (reduced from 3 VA/sq ft in prior NEC editions). Always add the small appliance circuits (1,500 VA each, minimum 2) and laundry circuit (1,500 VA) before applying demand factors.