General Lighting & Receptacle Branch-Circuit Calculator
Size general lighting and receptacle branch circuits under NEC Articles 210 and 220 — with occupancy VA/ft² lookup, custom VA entry, continuous-load factor, receptacle and dedicated-load configuration, and a circuit designer with self-test mode.
Overview
General lighting and receptacle branch circuits are among the first circuits sized on any commercial or residential project, and Articles 210 and 220 are among the most frequently referenced NEC sections in daily design practice. This calculator sizes branch circuits for general illumination and receptacle loads: enter floor area and select the occupancy type to pull the correct NEC Table 220.12 VA/ft² value (or enter a custom VA/ft²), configure general receptacle loads (15 A at 120 V, or special receptacle), and add dedicated loads. The continuous-load rule (125% on the circuit breaker and minimum conductor ampacity) is applied automatically, with an option to specify mixed continuous and non-continuous portions. The Loads tab provides a breakdown of connected load vs. calculated load vs. sizing load — three distinct values that are routinely confused. The Designer tab presents a branch-circuit layout tool showing how loads distribute across circuits. The Trace tab walks through the NEC Article 210 / 220 calculation sequence with code citations. A Self-Test tab runs the calculation logic against deterministic test cases. Five preset occupancy scenarios cover Small Office, Retail Space, Classroom, Receptacle-Heavy, and Dwelling Unit, with an Undersized scenario for learning what a violation looks like. The Learn tab covers the critical distinctions between connected load, calculated load, and sizing load; common branch-circuit mistakes; continuous vs. non-continuous load treatment; and NEC edition changes (2017, 2020, 2026). Supports NEC Articles 120, 210, and 220.
App preview
A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.
Inside the lab
What you'll do
- 01Look up the general lighting VA/ft² value from NEC Table 220.12 for a given occupancy type and calculate the total general lighting load for a defined floor area
- 02Distinguish connected load, calculated load, and sizing load and explain why all three values are different and matter
- 03Apply the 125% continuous-load multiplier to both the minimum conductor ampacity and the overcurrent device rating for a circuit serving continuous loads
- 04Configure a 15 A branch circuit for general receptacle loads and verify that the circuit loading does not exceed the 80% continuous-load limit
- 05Identify at least three common branch-circuit sizing mistakes the tool guards against and explain the NEC provision each mistake violates
- 06Compare how NEC 2017, 2020, and 2026 editions differ in their treatment of general lighting and receptacle branch-circuit requirements
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