UNIT 2.3 — LOAD CALCULATIONS

Branch circuits and dwelling load basics

CERT 2 · Residential Wiring · ~12 min

Community content — not verified by a licensed electrician. Lessons and questions here are written for study practice and pinned to NEC 2023. Code editions and local amendments vary by jurisdiction. Always confirm against your adopted code book and your licensing board's published exam outline before test day.

A dwelling's service size comes from a standard load calculation. It starts with general lighting at 3 VA per square foot of habitable area (NEC Table 220.12): a 1 500 ft² home starts at 4 500 VA before anything is plugged in.

Fixed minimums stack on top: two 20 A small-appliance branch circuits for the kitchen at 1 500 VA each (220.52), plus one 1 500 VA laundry circuit (220.53) — 4 500 VA of mandatory allowance in almost every exam problem. Critically, these are added to the lighting load BEFORE demand factors are applied.

Because not everything runs at once, demand factors discount the total (NEC 2023 Table 220.45; the same table was numbered 220.42 in the 2017 and 2020 editions). The tiers are: first 3 000 VA at 100%, from 3 001 to 120 000 VA at 35%, and anything above 120 000 VA at 25%. Most dwellings never reach the third tier, but exams include it. Fixed appliances, ranges, dryers, and HVAC are then added under their own rules.

Exam focus: the 3 VA/ft² figure, the 1 500 VA circuits, and the 3 000 VA / 35% demand split. Write every calculation vertically, one operation per line.

General lighting

3 VA / ft²

Small appliance + laundry

3 × 1 500 VA

Demand tiers

100% / 35% / 25%

Knowledge check

Quiz — 3 questions

1. General lighting load for a 2 000 ft² dwelling:

2. The minimum small-appliance branch circuits required in a dwelling kitchen:

3. Under the standard method, dwelling load from 3 001 to 120 000 VA counts at:

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