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Electrical Service Sizing
Dwelling unit and multifamily building service calculations per NEC Article 220. ← Back to Tools
Project Information (optional · click to expand)
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Firm
Project
Fields populate the Load Letter output (opening paragraph, project info table, building systems summary, transformer / CT cabinet / 800A boilerplate). Firm info can be remembered per-device; project info is per-project (not saved). Tool is generic — enter your own firm details.
Step 1 · Project Type
New Construction or Addition
New construction routes through §220.82 / §220.82×N+Part III / §220.84 based on dwelling-unit count and §220.84 qualification. Addition routes through §220.83 with auto-detected (A) vs (B) path based on whether new AC or electric heat is being installed.
Step 2 · Existing Service
Existing Service & §220.83 Path
Step 2 · Unit Types & Loads
Units
Each card is one dwelling-unit TYPE (set qty to the number of identical units in the building) or the common-area. Expand a card to configure SF, HVAC, appliances, and EV. Method auto-detects from total dwelling-unit count + §220.84 qualification (electric cooking + electric HVAC per §220.84(A)).
House Load · Common Area · §220.84(B) Part III
Common-area loads (corridors, basement, elevators, fire pump, common HVAC and pumps, common-area EV chargers) calculated under Article 220 Part III. For single-family work leave it empty; for multifamily it gets added to the dwelling demand per §220.84(B).
Step 3 · Service Voltage
Service Voltage & Sizing
Per PSE&G IRES Table 2-1. 3Φ supply is not normally available for residential service per IRES Tables 6-1/6-2 footnote; selecting 3Φ for §220.82/83/84 will surface a warning. Transformer service type auto-derived from the recommended kVA: overhead/UG up to 100 kVA (1Φ) / 300 kVA (3Φ); pad-mount above that to 167 / 1500 / 3000 kVA; customer-owned above the pad-mount cap. Voltage class affects amperage calc, CT cabinet threshold, max service size, and transformer sizing.
LED lighting, EVSE, electronic ballasts/drivers, VFDs, switching power supplies. Per NEC §310.15(E)(3), when the major portion of the load is nonlinear, the neutral counts as a current-carrying conductor due to harmonics. Auto-set based on new-construction status and EVSE presence — toggle to override.
Wire sizing per NEC §310.12 (one-family / dwelling-unit 83 % rule) and Table 310.16 (75 °C Cu THWN-2). Current-carrying conductor (CCC) count per raceway is auto-derived from the service voltage and nonlinear-load toggle per §310.15(E). Above 3 CCCs / 30 °C ambient triggers §310.15 adjustment — Table 310.16 is used in that case instead of §310.12. GEC sized per Table 250.66 with §250.66(A)/(B)/(C) caps when the listed electrode is the sole electrode (concrete-encased cap = 4 AWG, rod/pipe/plate = 6 AWG, ground ring = 2 AWG).
Results
Output format:
Per 2020 NEC per N.J.A.C. 5:23-3.16 — Article 215 (§215.2), Article 220 Parts II–IV (§§220.12, 220.42, 220.52, 220.53, 220.54, 220.55, 220.60, 220.82, 220.83, 220.84), Article 230 (§§230.42, 230.79), Article 240 (§240.6), Article 250 (§§250.50, 250.52, 250.66 + Table 250.66), Article 310 (§§310.10(G), 310.12, 310.15, 310.16), Article 430 (§430.24), Article 625 (§§625.41, 625.42), and N.J.A.C. 5:23-3.16. Verify all calculations against current adopted code edition. Service entrance and feeder conductor sizing per Article 310 is included for copper at 75 °C THWN-2; verify aluminum or other temperature ratings against manufacturer ampacity tables. Green Stories LLC is a building design and consulting firm.