Service Load Calculations — Worked Examples (Article 120 Parts III–IV, 310.12, 230.42, Table 250.66, 450.5)
Services & SDS is the Master exam's biggest calculation block (8 of 30 scored calc items; Journeyman 4). Every problem is one of: the dwelling standard method, the dwelling optional method, the existing dwelling table, the multifamily optional table, a commercial building (lighting + receptacles + kitchen equipment + motors), sizing the service conductors / neutral / GEC, or a transformer primary/secondary. 2026 changes that move the answers: Article 220 → 120; dwelling general lighting 2 VA/ft² (was 3); optional-method first tier 8 kVA; EVSE at nameplate or 7200 VA; existing-dwelling Table 12
NFPA 70 National Electrical Code, 2026 edition · Reviewed 2026-09-19
Services & SDS is the Master exam's biggest calculation block (8 of 30 scored calc items; Journeyman 4). Every problem is one of: the dwelling standard method, the dwelling optional method, the existing dwelling table, the multifamily optional table, a commercial building (lighting + receptacles + kitchen equipment + motors), sizing the service conductors / neutral / GEC, or a transformer primary/secondary. 2026 changes that move the answers: Article 220 → 120; dwelling general lighting 2 VA/ft² (was 3); optional-method first tier 8 kVA; EVSE at nameplate or 7200 VA; existing-dwelling Table 120.83 rewritten. Written from the 2026 text (viewer p.81–90, 119–120, 223, 151, 422–424).
1. Dwelling — standard method (Article 120 Part III)
| Step | Rule | Amount |
|---|---|---|
| General lighting | 120.41 | 2 VA/ft² of floor area (outside dimensions; exclude open porches, unfinished spaces not adaptable, detached garages) |
| Small appliance | 120.52(A) | 1500 VA × each 20 A small-appliance circuit (minimum two) |
| Laundry | 120.52(B) | 1500 VA |
| Demand on the three above | Table 120.45 | first 3000 VA at 100 %; 3001–120,000 VA at 35 %; remainder 25 % |
| Fastened-in-place appliances | 120.53 | nameplate; 75 % where four or more (not ranges, dryers, space heating, A/C, EVSE) |
| Dryers | 120.54 / Table 120.54 | 5000 W or nameplate, whichever larger; 1–2 at 100 %, 3–5 at 80 %, 6 at 75 %… |
| Ranges / cooking > 1¾ kW | Table 120.55 | Column C: one range ≤ 12 kW = 8 kW; Note 1: + 5 % per kW over 12 kW |
| Heating vs A/C | 120.6 / 120.51 / 120.50 | the larger of the two (noncoincident); heat at 100 %; A/C per 440 |
| Motors | 120.50 | 125 % of the largest motor (430.24) |
| EVSE | 120.57 | nameplate, or 7200 VA where none |
Example A — 2400 ft² dwelling, two small-appliance circuits, laundry, 12 kW range, 5 kW dryer, 4.5 kW water heater, 1.2 kW dishwasher, 0.8 kW disposal, 1 kW microwave (fastened), 10 kW electric heat, 4 kW (17 A) A/C, 120/240 V:
This is where the public part ends.
The rest of this lesson, its quiz, all 8 lessons in the module and every mock exam open with the 7-day pass for $9. If you stay, it comes off lifetime.