Overview of Chapter 2
Chapter 2 covers the design and protection of the electrical distribution system from the utility service point through feeders and branch circuits to the final outlets. It includes some of the most calculation-heavy material in the NEC, particularly load calculations for branch circuits and feeders. Mastery of this chapter is essential for the exam.
Exam Tip: Expect numerous calculation questions drawn from Articles 210, 215, 220, and 230. Practice computing branch-circuit loads, feeder loads, and service sizes until the process is second nature.
Branch Circuits (Article 210)
Branch circuits are the final link between the overcurrent protective device and the utilization equipment. Article 210 establishes ratings, permissible loads, required circuits, and receptacle outlet requirements.
Branch Circuit Ratings
Standard branch circuit ratings are 15, 20, 30, 40, and 50 amperes. The rating is determined by the ampere rating of the overcurrent device.
- 15A and 20A circuits: General-purpose lighting and receptacle circuits. A 15A receptacle is permitted on a 20A circuit but not vice versa.
- 30A circuits: Typically used for specific appliance loads such as dryers.
- 40A and 50A circuits: Used for cooking equipment, large appliances, and similar loads.
Required Branch Circuits
Dwelling units require at minimum:
- Two or more 20A small-appliance branch circuits serving the kitchen, dining room, pantry, and similar areas.
- At least one 20A branch circuit for bathroom receptacle outlets.
- At least one 20A branch circuit for laundry receptacle outlets.
GFCI and AFCI Protection
Article 210.8 requires ground-fault circuit-interrupter (GFCI) protection for receptacles in bathrooms, kitchens, garages, outdoors, crawl spaces, basements, laundry areas, and other specified locations. Article 210.12 requires arc-fault circuit-interrupter (AFCI) protection for most branch circuits in dwelling unit living areas.
Feeders (Article 215) and Load Calculations (Article 220)
A feeder supplies one or more branch-circuit panelboards. Feeder conductors must be sized to carry the calculated load as determined by Article 220.
Standard Calculation Method
- General lighting: Calculated at 3 VA per square foot for dwellings. Apply demand factors from Table 220.42 for loads over 3000 VA.
- Small-appliance and laundry loads: Each small-appliance circuit is calculated at 1500 VA; laundry at 1500 VA.
- Fixed appliances: Four or more fastened-in-place appliances (other than ranges, dryers, HVAC) may use a 75% demand factor.
- Range loads: Use Table 220.55 demand factors.
Services (Article 230)
The service is the point where the utility supply connects to the premises wiring. Article 230 covers everything from service drops and laterals to service equipment and disconnects.
- Generally only one service is permitted per building, with limited exceptions.
- The service disconnecting means must be installed at a readily accessible location nearest the point of entrance of the service conductors.
- A maximum of six disconnects (the “six-throw rule”) is permitted for each service or set of service-entrance conductors.
- Service conductors must have overcurrent protection, and service equipment must be listed and suitable for the purpose.
Overcurrent Protection (Article 240)
Article 240 establishes requirements for overcurrent protective devices (fuses and circuit breakers) to protect conductors and equipment from overcurrent conditions.
- Conductors must be protected at their ampacity per the applicable tables, with exceptions for tap conductors and specific equipment circuits.
- Standard overcurrent device ratings are: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, and higher (240.6(A)).
- The next standard size up rule (240.4(B)) allows the next higher standard overcurrent device rating when the ampacity of the conductor does not correspond to a standard device rating, subject to certain limitations.
Grounding and Bonding (Article 250)
Article 250 is one of the most extensive and frequently tested articles in the NEC. It addresses system grounding, equipment grounding, bonding, and grounding electrode systems.
- System grounding establishes a reference to earth and limits voltage imposed by lightning or line surges.
- Equipment grounding conductors (EGCs) provide a low-impedance fault-current path to facilitate overcurrent device operation.
- The grounding electrode system must include all electrodes present at a building, bonded together: metal water pipe, metal building frame, concrete-encased electrode (Ufer ground), ground rings, and rod or pipe electrodes.
Key Rule: The equipment grounding conductor and the grounded (neutral) conductor must not be connected together on the load side of the service disconnecting means, except in separately derived systems.
Surge Protection (Article 285)
Article 285 covers surge-protective devices (SPDs) installed on premises wiring systems rated up to 1000 volts. SPDs protect equipment from transient voltage surges caused by lightning, utility switching, or other events.
