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The service conductor sizing calculator determines the minimum service entrance conductor size for residential, commercial, and industrial electrical services per NEC Article 230. Service conductors connect the utility supply to the service entrance equipment (meter socket and main disconnect), and must be sized to safely carry the total calculated load demand current.
Service conductor sizing follows a three-step process: calculate total connected load, apply demand factors to determine maximum demand current, then select conductors from NEC Table 310.12 (or manufacturer specifications for service entrance cable). NEC Article 220 provides detailed load calculation methods, including general lighting loads (3 VA/sq ft residential), appliance loads, HVAC loads, and special loads.
Demand factors account for the statistical reality that not all electrical loads operate simultaneously at full capacity. NEC Article 220 specifies demand factors for different load types. Residential demand factors: first 3000 VA at 100%, next 117,000 VA at 35%. Large motor demand may add 25% of the largest motor FLA to the total. Actual demand monitoring (with smart meters) often reveals demand factors of 40-60% for residential applications.
For single-phase services, current I = VA / V. For three-phase services, I = VA / (√3 × V). Standard service sizes for residential: 100A (minimum per NEC 230.79), 150A, 200A, 400A. Commercial and industrial services may be 400A, 800A, 1200A, 2000A, or higher for large facilities.
Aluminum conductors are almost universally used for service entrance conductors in residential construction due to their lower cost and lighter weight. However, aluminum connections require anti-oxidant compound and rated terminals. The NEC minimum service size of 100A (for single-family dwellings) requires AWG 4 aluminum or AWG 6 copper service entrance conductors.
Demand current = total VA × demand_factor / (V for single-phase, √3 × V for three-phase). Service rating is rounded up to the nearest standard size (25, 30, 40, 50, 60, 100, 125, 150, 175, 200, 225, 400A). Conductor AWG is selected from NEC Table 310.12 as the smallest gauge with ampacity ≥ demand current.
Select the service equipment (meter, main breaker, panel) rated at the calculated service amps. The service conductors must have ampacity ≥ demand current. For residential, 200A is standard for modern homes with EV charging, heat pumps, and high-demand appliances. Commercial facilities should include 25% spare capacity for future load growth.
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48 kVA total load at 80% demand on 240V single-phase gives 160A demand — use 175A service with 2/0 copper or 3/0 aluminum service entrance conductors.
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150 kVA at 75% demand on 208V three-phase gives ~312A — requires 350A service (next standard size above 325A) with 350 kcmil copper conductors.
NEC 230.79(C) requires a minimum 100A service for any single-family dwelling or individual apartment in a multi-family building. Most modern homes need 150-200A due to EV chargers, heat pumps, and other high-demand loads.
A demand factor is the ratio of maximum demand to total connected load. Since not all loads operate simultaneously, the actual maximum current is typically lower than the sum of all individual loads. NEC Article 220 specifies standard demand factors by load type.
Aluminum is significantly less expensive and lighter than copper. Service entrance conductors are large (AWG 4/0 to 750 kcmil) where aluminum's cost advantage is greatest. Proper termination with anti-oxidant compound and AL-rated lugs eliminates corrosion concerns.
NEC 230.79(A)-(C) allows smaller services for limited loads: 15A for single branch circuit loads, 60A for multi-circuit dwellings with no electric heating. But 230.79(C) requires 100A for single-family dwellings. Local amendments may require 200A.
Use NEC Article 220 Part III (optional method for existing dwellings) or Part II (standard method). Standard: 3 VA/sq ft general lighting + 3000 VA small appliance circuits + actual nameplate loads for fixed appliances, HVAC, EV chargers, etc.
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