What NEC article covers load calculations?

NEC Article 220 covers branch circuit, feeder, and service load calculations. The Optional Method for dwellings is in 220.82.

What NEC article covers grounding?

NEC Article 250 covers grounding and bonding, including service grounding electrode system, equipment grounding conductors, and bonding requirements.

What NEC article covers transformers?

NEC Article 450 covers transformers, including overcurrent protection requirements in Table 450.3(B).

NEC Code Quick Reference — NEC 2023 Article Lookup

Art. 220

Branch-Circuit, Feeder, and Service Load Calculations

The primary load calculation article. Covers demand factors, optional method for dwellings, and general lighting loads.

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NEC Article 220 governs how electrical loads are calculated for branch circuits, feeders, and service entrances. The Standard Method (Part II) and Optional Method (Part IV) produce different service sizes for the same dwelling.

220.12General lighting load: 3 VA/ft² for dwelling units, 2 VA/ft² for warehouses, 3.5 VA/ft² for offices.

220.42Demand factors for general lighting: first 3,000 VA at 100%, next 117,000 VA at 35%, over 120,000 VA at 25%.

220.52Small appliance branch circuits: 1,500 VA per circuit, minimum 2 circuits. Laundry circuit: 1,500 VA.

220.54Dryer demand: 5,000 W or nameplate, whichever is larger. 5+ dryers: Table 220.54 DF applies.

220.55Range/oven demand per Table 220.55: single 12 kW range = 8 kW demand.

220.82Optional Method for single-family dwellings: 100% of first 10 kVA + 40% of remainder. Simpler than Standard Method.

220.84Multi-family dwelling demand factors per Table 220.84. 10 units: 43%, 30 units: 35%, 50+ units: 26–28%.

Art. 210

Branch Circuits

Requirements for individual and multi-outlet branch circuits including GFCI, AFCI, conductor sizing, and outlet spacing.

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210.8GFCI protection required: bathrooms, garages, outdoors, crawl spaces, unfinished basements, kitchens (all countertop receptacles), boathouses, rooftops, boat hoists.

210.11Minimum 2 small appliance circuits (20A) and 1 laundry circuit (20A) required for dwelling units.

210.12AFCI protection required for all 120V, 15/20A branch circuits in dwelling unit bedrooms, family rooms, living areas, hallways, closets.

210.19(A)Conductor ampacity must be ≥ 125% of continuous load + 100% of non-continuous load.

210.20(A)Branch circuit OCPD rating ≥ 125% of continuous load.

210.52Dwelling receptacle spacing: every 12 ft along walls (6 ft from any point). Kitchen counters: every 4 ft, within 2 ft of ends.

Art. 310

Conductors for General Wiring

Ampacity tables, temperature ratings, insulation types, and installation rules for conductors in conduit, cable, and free air.

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310.15(A)Base ampacity from NEC Table 310.16 assumes ≤3 current-carrying conductors in a raceway at 30°C ambient.

310.15(B)Temperature correction factors: ambient above 30°C reduces allowable ampacity. Use correction factor from NEC Table 310.15(B)(1).

310.15(C)Conduit fill adjustment: 4–6 conductors = 80%, 7–9 = 70%, 10–20 = 50%, 21–30 = 45%, 31–40 = 40%, 41+ = 35%.

310.15(E)Neutral conductors carrying only unbalanced current do not count as current-carrying for fill derating.

110.14(C)Termination temperature limits: most equipment rated 60°C or 75°C, so 90°C wire must be sized using 75°C column value.

Art. 300

Wiring Methods — General Requirements

Installation rules for all wiring methods: conduit fill, wet/dry locations, protection requirements, and conductor bundling.

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300.3All conductors of a circuit (including neutral and EGC) must be installed in the same raceway, cable, or trench.

300.5Underground burial depths: 24 in. for direct burial, 18 in. in RMC/IMC, 12 in. for residential branch circuits under ≤120V, ≤20A with GFCI.

300.11Raceways and cables must be securely fastened. Ceiling grid wires cannot support wiring methods unless listed for that use.

300.14Minimum 6 inches of free conductor at each outlet box, with 3 inches extending outside box.

Art. 334

Non-Metallic Sheathed Cable (NM / Romex)

Installation requirements for NM-B cable in residential and light commercial applications including permitted uses and prohibited locations.

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334.10Permitted in one- and two-family dwellings, multi-family buildings (wood-framed), other structures not exceeding 3 floors above grade.

334.12Not permitted: in commercial garages, theaters, motion picture studios, storage battery rooms, hazardous locations, embedded in poured concrete.

334.15Must be protected from physical damage. Exposed in attics and crawl spaces: guard strips required within 6 ft of access.

334.30Secure within 12 in. of every box, and every 4.5 ft throughout run.

Art. 240

Overcurrent Protection

Rules for fuses and circuit breakers including standard sizes, conductor protection, and location requirements.

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240.4(D)Maximum OCPD for small conductors: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A. These are hard limits — cannot be exceeded.

240.6(A)Standard ampere ratings: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000A.

240.21Tap conductors: 10-ft tap rule (10 ft max, ampacity ≥ 10% of upstream OCPD), 25-ft tap rule (terminated in single OCPD ≤ feeder ampacity).

240.24Overcurrent devices must be readily accessible, not in bathrooms, not over steps, not in clothes closets.

Art. 110

General Requirements for Electrical Installations

Fundamental requirements including interrupting ratings, working space clearances, and conductor termination temperature limits.

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110.9Equipment must have interrupting rating not less than available fault current at the point of installation.

110.14(C)Termination temp limits: ≤100A or 14–1 AWG = 60°C unless marked 75°C. Over 100A or 1/0 AWG and larger = 75°C unless marked otherwise.

110.26(A)Working space depths: Condition 1 = 3 ft (no exposed live parts opposite), Condition 2 = 3.5 ft, Condition 3 = 4 ft. For 601–2500V: 4/5/6 ft.

110.26(C)Dedicated equipment space: 6 ft wide × height of equipment for electrical panels. No piping, ducts, or foreign equipment in this space.

110.34Over 1000V working clearances: minimum 3 ft for <2.5 kV. Includes elevation of unguarded live parts.

Art. 250

Grounding and Bonding

Complete grounding requirements including grounding electrode system, equipment grounding conductors, and bonding for piping and structures.

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250.24Service grounding: neutral must be grounded at service entrance. Grounded conductor must be routed with phase conductors.

250.50Grounding electrode system: all available electrodes (metal water pipe ≥10 ft, building steel, concrete-encased electrode, ground ring) must be bonded together.

250.52Permitted electrodes: metal underground water pipe ≥10 ft, metal building structure, concrete-encased (Ufer) — 20 ft of ≥½ in. rebar, ground ring, rod/pipe/plate.

250.53Ground rod: minimum 8 ft driven into earth. If resistance >25Ω, second electrode required. Most inspectors require dual rods by default.

250.66GEC sizing per Table 250.66: based on largest service-entrance conductor. 2/0 Cu service → 4 AWG Cu GEC min.

250.122EGC sizing per Table 250.122: based on OCPD rating. 100A OCPD → 8 AWG Cu EGC min. 200A → 6 AWG Cu.

250.104Metal water and gas piping must be bonded at first point of entry or at service equipment.

Art. 450

Transformers and Transformer Vaults

Installation and protection requirements for transformers 600V and below, including NEC Table 450.3(B) overcurrent protection limits.

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450.3(B)Transformers ≤600V: primary OCP ≤ 125% of primary FLA (with secondary protection), or ≤ 250% (primary-only protection).

450.3(B)Secondary OCP: ≤ 125% of secondary FLA. Secondary conductors ≤ 10 ft to a panelboard may qualify for tap rule exception.

450.9Ventilation: transformers must have adequate ventilation. Dry-type transformers >112.5 kVA in fire-resistant rooms only.

450.14Disconnecting means required within sight of transformer, or lockable in open position.

Art. 230

Services

Service entrance conductor requirements, service disconnect location, number of services, and service conductor sizing.

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230.42Service conductors must have ampacity ≥ the calculated load per Art. 220. Minimum 100A for one-family dwellings (230.79(C)).

230.70Service disconnect must be installed at a readily accessible location nearest the entrance of service conductors into the building.

230.71Maximum 6 disconnects for a single service. Six-circuit rule (one-hand rule) applies.

230.79(C)Minimum 100A service for any one-family dwelling.

Art. 430

Motors, Motor Circuits, and Controllers

Motor branch circuit sizing, overload protection, disconnecting means, and controller requirements.

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430.6(A)Use NEC Table 430.248/250 FLA values (not nameplate amps) for branch circuit and feeder sizing.

430.22Branch circuit conductors: ≥ 125% of motor FLA (from 430.248/250 tables).

430.32Overload protection: ≤ 115% of FLA for motors marked "service factor" ≥ 1.15 or temp rise ≤ 40°C. Otherwise ≤ 125%.

430.52Branch circuit OCPD per Table 430.52: inverse time breaker = 250% of FLA (max starting protection).

430.102Disconnect required within sight of motor controller and within sight of motor (or lockable in open position).

Art. 500–503

Hazardous (Classified) Locations

Class/Division and Zone classification system for locations with flammable gases, vapors, dusts, and fibers. Equipment selection and installation rules.

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500.5Class I: flammable gases/vapors. Class II: combustible dust. Class III: ignitable fibers. Division 1: normally present. Division 2: abnormal conditions only.

501.10Class I, Div. 1 wiring: threaded RMC, threaded steel IMC, or Type MI cable with listed fittings only.

500.8Equipment must be listed and labeled for the class, division, and gas group (A, B, C, D for Class I).

501.15Seals required: within 18 in. of explosion-proof enclosures, at boundary between classified and unclassified areas.

Art. 700–702

Emergency, Legally Required Standby, and Optional Standby Systems

Requirements for emergency lighting, legally required standby power, optional standby systems, and automatic transfer switches.

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700.3Emergency systems must be tested periodically. Acceptance test required. AHJ may witness test.

700.12Emergency sources: storage battery, UPS, generator, separate service, fuel cell. Must supply power within 10 seconds.

700.26Emergency circuits must be kept entirely independent of all other wiring. Cannot share raceways, boxes, or cabinets with normal wiring.

702.5Optional standby systems: capacity must be sufficient to supply all loads intended to operate simultaneously.

Art. 690

Solar Photovoltaic (PV) Systems

Installation requirements for PV arrays, inverters, conductors, disconnects, rapid shutdown, and utility interconnection.

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690.12Rapid shutdown required for PV systems on buildings. Conductors within the array boundary must be de-energized within 30 seconds.

690.15Disconnecting means required for each inverter, charge controller, and AC/DC module. Must be accessible and within sight.

690.8PV circuit conductor sizing: use 125% of maximum circuit current. Multiply Isc by 125% for conductor and OCPD sizing.

690.64Point of connection: the sum of 125% of inverter output + main breaker rating cannot exceed 120% of the busbar rating.

Art. 625

Electric Vehicle (EV) Charging Systems

EVSE installation requirements, branch circuit sizing, ventilation, and load calculation rules for EV charging stations.

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625.17EVSE branch circuit: must be a dedicated circuit. Conductor sized at 125% of the maximum EVSE load (continuous load rule).

625.42Personnel protection: EV charging outlets must have GFCI protection for Level 1 and Level 2 equipment in garages and outdoor locations.

625.54Indoor charging: sealed battery systems that produce hydrogen require ventilation or listed sealed equipment.

220.57EV load calculation for dwelling: 7,200 VA or nameplate, whichever is larger, at 100% for load calculations.

Sec. 8

Circuit Loading and Demand Factors

CEC Section 8 — service ampacity calculation, dwelling-unit and commercial demand factors, basic and additional loads.

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Section 8 governs the calculation of circuit and feeder loads for single dwellings, apartments, and commercial occupancies. The Calculated Load is compared against service rating per Rule 8-104.

8-102Voltage drop ≤3% on branch circuits and ≤5% on feeder + branch combined.

8-104Maximum continuous load: 80% of conductor ampacity / OCP rating (matches NEC 210.20(A)).

8-106Use of demand factors for service / feeder calculation. Optional method for dwellings.

8-108Number of branch circuits required — small-power circuits, kitchen receptacle circuits, laundry.

8-200Single-dwelling calculated load — basic load 5,000 VA on first 90 m², additional 1,000 VA per 90 m² over.

8-202Apartment / row-housing: 100% of largest unit + 65% of next four + 40% of remainder.

8-210Schools, hotels, hospitals — Table 14 demand factors apply on general lighting and small power.

Sec. 4

Conductors — Ampacity and Selection

CEC Section 4 — ampacity tables (T1, T2, T4), termination temperature, ambient and bundling derating, neutral sizing.

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Section 4 is the CEC equivalent of NEC Article 310. The choice between Tables 1, 2, 4 depends on installation method (free air, raceway, cable). T5A/T5C provide ambient and bundling correction factors.

R4-004Ampacity of conductors in raceway / cable — use Table 2 (90 °C insulation, ≤3 conductors).

R4-006Terminations limited to 75 °C rating on most equipment ≤100 A.

R4-008Single conductors in free air — use Table 1.

R4-024Neutral conductor sizing — full or reduced per balanced harmonic content.

T5AAmbient correction factors when not 30 °C; multiply ampacity by factor before comparison.

T5CBundling correction factors for >3 current-carrying conductors in a raceway / cable.

Sec. 14

Protection and Control

CEC Section 14 — overcurrent protection, breaker/fuse interrupting rating, series rating, GFCI / AFCI requirements.

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Section 14 sets requirements for protective devices including breakers, fuses, and ground-fault devices. Mirrors NEC Article 240 but uses Table 13 for standard sizes.

R14-100Each ungrounded conductor must be protected from overcurrent. Tap-rule exceptions per R14-100(2).

R14-104Breaker / fuse not larger than conductor ampacity; next standard size up where ampacity does not match.

R14-200Interrupting rating must be ≥ available fault current at the point of installation.

R14-308Series-rated combinations: only when tested and listed; field labeling required.

T13Standard breaker / fuse ratings: 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 125 A... ≤6000 A.

Sec. 10

Grounding and Bonding

CEC Section 10 — system grounding, equipment bonding, grounding-electrode conductor, bonding jumper sizing.

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Section 10 governs the establishment of a fault-clearing path and equipotential bonding. Mirrors NEC Article 250 in scope and intent.

R10-100System grounding required at service for all systems below 750 V to ground.

R10-204Grounding electrode — minimum two ground rods or alternate per R10-700.

R10-806Bonding-conductor size — based on largest ungrounded supply conductor; Table 16.

R10-808Equipment bonding jumper inside service equipment.

T16Minimum bonding conductor sizes; T17 for grounding-electrode conductor.

Sec. 24

Patient Care Areas — Healthcare Facilities

CEC Section 24 — basic / intermediate / critical care area requirements, isolated power systems, redundant grounding.

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Section 24 references CSA Z32 for healthcare facilities. Patient-care areas are classified by risk (basic, intermediate, critical) which drives redundant grounding, isolated power, and emergency power requirements.

R24-102Classification: Basic, Intermediate, Critical care area definitions per CSA Z32.

R24-104Receptacles in patient-care areas — hospital-grade, redundant grounding.

R24-202Isolated power systems in critical care — LIM (Line Isolation Monitor) required.

R24-300Essential electrical system — Class 1 (critical) restored ≤10 s.

Sec. 46

Emergency Power Supply and Life-Safety Systems

CEC Section 46 — emergency / standby power, transfer-time classes, fire-alarm circuits, exit/emergency lighting.

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Section 46 specifies wiring methods and circuit isolation for emergency / standby systems. Coordinated with CSA C282 (generators) and CAN/ULC-S524 (fire alarm installation).

R46-100Application — emergency lighting, fire alarm, smoke control, elevators required by code.

R46-108Wiring of emergency systems — separated from normal feeders by 600 mm or barrier.

R46-204Emergency / exit lighting — minimum 30 min duration (typ. 60-120 min per OBC).

R46-300Fire-alarm circuits — installed per CAN/ULC-S524, supervised, dedicated branch from life-safety panel.

Sec. 26

Installation of Electrical Equipment

CEC Section 26 — panelboards, distribution boards, transformers, capacitors, ESA Bulletin 2-9-9 working space.

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Section 26 governs installation of distribution and utilization equipment. ESA Bulletin 2-9-9 clarifies working-space requirements (Rule 2-308) for Ontario.

R2-308Working space in front of equipment 750 V or less — min 1.0 m clearance; 600 mm width.

R26-110Distribution boards / panelboards — installation, accessibility, identification.

R26-242Transformer overcurrent protection — primary 125-300% based on impedance; secondary as required.

T50Transformer OCP multipliers — primary / secondary.

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