Electrical: The Rules the Exam Asks For

A feeder is all the circuit conductors between the service equipment, the source of a separately derived system, or another power supply source and the final branch-circuit overcurrent device. On a house, that is the run from the main panel to a subpanel.

Electrical Code § art100

A branch circuit is the circuit conductors between the final overcurrent device protecting the circuit and the outlet or outlets. A multiwire branch circuit has two or more ungrounded conductors with voltage between them and one neutral with equal voltage to each, connected to the system neutral.

Electrical Code § art100

A grounding electrode is a conducting object that makes a direct connection to earth. The grounding electrode conductor (GEC) connects the system grounded conductor or the equipment to a grounding electrode, or to a point on the grounding electrode system.

Electrical Code § art100

The main bonding jumper is the connection at the service between the grounded circuit conductor (in a dwelling, the neutral) and the equipment grounding conductor, the supply-side bonding jumper, or both. A separately derived system, a power supply output other than a service with no direct connection to another source except through grounding and bonding, gets the same connection through its own system bonding jumper.

Electrical Code § art100

A service lateral is the underground conductors between the utility's electric supply system and the service point. A service drop is the overhead conductors between the utility and the service point. The service point is where the utility's facilities connect to the premises wiring.

Electrical Code § art100

A dwelling unit needs two or more 20-ampere small-appliance branch circuits for the receptacle outlets the kitchen-receptacle section requires. It also needs at least one 20-ampere laundry circuit with no other outlets, and one or more 120-volt, 20-ampere bathroom circuits supplying the required bathroom receptacle outlets and any countertop or similar work-surface receptacle outlets, with no other outlets, except that a circuit serving a single bathroom may also supply other equipment in that bathroom. It also needs at least one 120-volt, 20-ampere garage circuit for the receptacle outlets of an attached garage or a powered detached garage, with no other outlets, except that it may supply outdoor receptacle outlets and, where it serves a single-vehicle-bay garage, other equipment in that garage. Garage receptacle outlets beyond the required ones may be served by additional branch circuits rated 15 amperes or greater.

Electrical Code § 210.11

In the kitchen, pantry, breakfast room, dining room, and similar areas of a dwelling unit, for the 125-volt, 15- and 20-ampere receptacle outlets this section governs, the two or more 20-ampere small-appliance circuits that 210.11(C)(1) requires serve all the wall, floor, and countertop receptacle outlets and the receptacle outlets for refrigeration equipment; in addition to those required receptacles, a receptacle outlet serving a specific appliance may be supplied from an individual branch circuit rated 15 amperes or greater. Those small-appliance circuits have no other outlets, except a receptacle installed solely to supply an electric clock in those rooms and receptacles for the supplemental equipment and lighting on gas-fired ranges, ovens, or counter-mounted cooking units. Receptacles serving kitchen countertops must be supplied by at least two small-appliance circuits, and no small-appliance circuit may serve more than one kitchen. In addition to the required receptacles, a switched receptacle permitted by the lighting-outlet rule, 210.70(A)(1) Exception No. 1, may be fed from a general-purpose 15- or 20-ampere circuit.

Electrical Code § 210.52

Receptacles are placed so that no point along the floor line of any wall space is more than 6 feet from a receptacle outlet. For receptacle spacing, wall space includes any wall 2 feet or wider, measured around corners and unbroken along the floor line by doorways, fireplaces, stationary appliances, or fixed cabinets without countertops. It also includes the space occupied by fixed panels in walls, but not sliding panels, and the space at fixed room dividers such as bar-type counters or railings. A receptacle that is part of a luminaire or appliance, controlled by a listed wall-mounted control device, inside a cabinet or cupboard, or more than 5-1/2 feet above the floor does not count toward the required outlets. A floor receptacle counts only if it is within 18 inches of the wall. A factory-installed or manufacturer-supplied receptacle on a permanently installed electric baseboard heater may serve as the required outlet for that wall space, provided it is not connected to the heater circuit.

Electrical Code § 210.52

Every multiwire branch circuit must have a means that simultaneously disconnects all its ungrounded conductors at the point where the circuit originates. All conductors of a multiwire circuit originate from the same equipment containing its overcurrent devices, except as the wiring-methods article permits.

Electrical Code § 210.4

In kitchens, pantries, breakfast rooms, dining rooms, and similar areas of dwelling units, countertop and work surfaces 12 inches or wider get 125-volt, 15- or 20-ampere receptacle outlets that do not count toward the general wall-space outlets. Along a countertop wall, no point along the wall line may be more than 24 inches horizontally from a receptacle outlet, except that none is required directly behind a range, counter-mounted cooking unit, or sink in the configuration the code's figure shows, and where a required outlet cannot go in the wall areas the figure shows, it goes as close as practicable to the countertop it serves without reducing the count. An island or peninsula need not have a receptacle, but if none is installed, provisions for adding one later are required. Countertop receptacles are located on or above the surface but not more than 20 inches above it, or in listed countertop or work-surface receptacle assemblies; receptacles made not readily accessible by appliances fastened in place, appliance garages, sinks or rangetops in the behind-the-range-or-sink configuration of Exception No. 1, or appliances occupying assigned spaces do not count as required outlets. Each 12 inches of multioutlet assembly containing two or more receptacles, installed in individual or continuous lengths, counts as one outlet.

Electrical Code § 210.52

On a single-phase circuit, current in amperes equals power in watts divided by voltage in volts. Two of the three quantities are given; the third is found from them. Example: a 1,500-watt heater on a 120-volt circuit draws 1,500 ÷ 120 = 12.5 amperes, assuming a resistive load with a power factor of 1.

Standard trade practice

In dwelling units, all 125- through 250-volt receptacles supplied by single-phase branch circuits rated 150 volts or less to ground need GFCI protection in these locations: bathrooms; garages and accessory buildings with a floor at or below grade level used for storage or work; outdoors; crawl spaces at or below grade; basements; kitchens; areas with sinks and permanent provisions for food preparation, beverage preparation, or cooking; within 6 feet of the top inside edge of a sink bowl; boathouses; within 6 feet of the outside edge of a bathtub or shower stall; laundry areas; and indoor damp and wet locations. Distances are measured along the shortest path a cord would follow without passing through a wall, floor, ceiling, or fixed barrier. The GFCI must be installed in a readily accessible location.

Electrical Code § 210.8

Two of the four exceptions to the dwelling GFCI locations: a receptacle that is not readily accessible and is on a branch circuit dedicated to electric snow-melting, deicing, or pipeline and vessel heating may follow those articles' own ground-fault rules instead, and a factory-installed receptacle mounted inside a bathroom exhaust fan assembly and not readily accessible is exempt unless its instructions or listing require GFCI.

Electrical Code § 210.8

For dwellings, all outdoor outlets, not only receptacles, on single-phase branch circuits rated 150 volts or less to ground and 50 amperes or less need GFCI protection, including outlets in garages with floors at or below grade, accessory buildings, and boathouses. If the equipment an outdoor outlet supplies is replaced, the outlet gets GFCI protection. The same not-readily-accessible receptacles on branch circuits dedicated to snow-melting, deicing, or pipeline and vessel heating are excluded, lighting outlets are excepted except that crawl-space lighting outlets at 120 volts or less still need GFCI under 210.8(C), and listed HVAC equipment was excepted only until September 1, 2026, the date on which the code says that exception expires.

Electrical Code § 210.8

GFCI protection is required for the branch circuit or outlet supplying certain appliances rated 150 volts or less to ground and 60 amperes or less, single- or three-phase, wherever they are installed: dishwashers, electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, microwave ovens, sump pumps, drinking water coolers and bottle-fill stations, vending machines, automotive vacuum machines, tire inflation machines, and high-pressure spray washing machines.

Electrical Code § 210.8

In dwelling units, all 120-volt, single-phase, 10-, 15-, and 20-ampere branch circuits supplying outlets or devices in kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, and similar areas need AFCI protection by one of the listed means. A listed combination-type AFCI protecting the whole branch circuit is the first of those means. Exception: an individual branch circuit supplying a fire alarm system installed per the fire-alarm article, run in metal raceway, metal auxiliary gutter, steel-armored cable, or Type MC or AC cable, with metal boxes, conduit bodies, and enclosures, needs no AFCI.

Electrical Code § 210.12

Where the wiring of a 120-volt, single-phase, 10-, 15-, or 20-ampere branch circuit in any location where AFCI is required — the 210.12(B) dwelling-unit rooms (kitchens, bedrooms, living areas, hallways, closets, laundry areas, and similar), dormitory-unit bedrooms, living rooms, hallways, closets, bathrooms, and similar rooms (not dormitory kitchens or laundry areas), hotel and motel guest rooms and suites, areas used exclusively as patient sleeping rooms in nursing homes and limited-care facilities, and areas designed for use exclusively as sleeping quarters in fire, police, ambulance, rescue, and ranger stations — is modified, replaced, or extended, the circuit must be AFCI-protected: either by one of the listed means, or by a listed outlet branch-circuit-type AFCI at the first receptacle outlet of the existing branch circuit. The AFCI itself is listed and installed in a readily accessible location.

Electrical Code § 210.12

The exception: an extension of the existing conductors of not more than 6 feet that adds no outlets or devices other than splicing devices needs no AFCI, and conductor length inside enclosures, cabinets, or junction boxes is not counted.

Electrical Code § 210.12

When a receptacle is replaced at an outlet that the code requires to be GFCI-protected, the replacement must provide GFCI protection, and the GFCI must be listed. Where the box is too small for a GFCI receptacle, a receptacle of the existing type may be installed if GFCI protection is provided upstream and the receptacle is marked "GFCI Protected" and "No Equipment Ground" as applicable. Replacement AFCI and GFCI receptacles go in readily accessible locations. Replacing a receptacle in the areas 210.12(A), (B), or (C) name — dwelling units and dormitory units, not the other sleeping occupancies of 210.12(D) — needs a listed outlet branch-circuit AFCI receptacle, a receptacle protected by one, or protection by a listed combination-type AFCI breaker. The 210.12(E) short-extension exception does not excuse AFCI on a receptacle replacement.

Electrical Code § 406.4

Where circuit conductors are spliced or terminated in a box, all equipment grounding conductors in the box are connected together. The connections are arranged so that removing a receptacle, luminaire, or other device does not break the equipment grounding path, which means a pigtail to the device rather than a daisy-chain through it. In a nonmetallic box, the equipment grounding conductors are arranged to connect to any device or fitting in the box that needs one.

Electrical Code § 250.148

An equipment bonding jumper is the connection between two or more portions of the equipment grounding conductor. A bonding jumper generally is a conductor that ensures the required electrical conductivity between metal parts that are required to be electrically connected, and bonding itself means connected to establish electrical continuity and conductivity.

Electrical Code § art100

A building or structure supplied by a feeder or branch circuit needs its own grounding electrode system, unless a single branch circuit with an equipment grounding conductor supplies it. The feeder carries an equipment grounding conductor to the building's disconnecting means and to its electrodes. The grounded conductor (neutral) is not connected to the equipment grounding conductor or to the electrodes at that building. Exception for older work: where an installation made under a previous edition that permitted it has no equipment grounding conductor run with the supply, no continuous metallic paths bonded between the buildings, and no ground-fault protection of equipment on the supply side, the grounded conductor may keep serving as the ground-fault return path.

Electrical Code § 250.32

A single rod, pipe, or plate electrode must be supplemented by an additional electrode of another type the code recognizes in 250.52(A)(2) through (A)(8), unless the single electrode has a measured resistance to earth of 25 ohms or less. Rod, pipe, and plate electrodes are free of nonconductive coatings and, if practicable, embedded below permanent moisture level. Where multiple rod, pipe, or plate electrodes are installed to meet the rule, they are at least 6 feet apart.

Electrical Code § 250.53

A rod or pipe electrode is installed with at least 8 feet in contact with the soil and driven to at least 8 feet. Where rock bottom is met, it is driven at an oblique angle no more than 45 degrees from vertical, or, where rock is met at that angle too, buried in a trench at least 30 inches deep. The upper end is flush with or below ground level unless the above-ground end and the grounding electrode conductor attachment are protected against physical damage.

Electrical Code § 250.53

A metal underground water pipe used as a grounding electrode must be supplemented by an additional electrode of another type the code recognizes in 250.52(A)(2) through (A)(8). The grounding path may not depend on water meters or filters for continuity. If the supplement is a rod, pipe, or plate, it follows the rod rules.

Electrical Code § 250.53

Equipment likely to need work while energized, at 1,000 volts nominal or less to ground, needs working space in front of it. The depth, measured from the exposed live parts or the enclosure front, comes from Table 110.26(A)(1) by voltage to ground and by what faces the equipment, except where the reliefs in 110.26(A)(1)(a) through (c) or another rule of the code allow less. The width is the equipment's width or 30 inches, whichever is greater, and must allow doors or hinged panels to open 90 degrees. The height runs from the floor to 6-1/2 feet or the equipment's height, whichever is greater; within that height, other equipment or support structures associated with the installation and located above or below the electrical equipment, such as concrete pads, may extend up to 6 inches beyond its front. Of the height rule's three exceptions, the one a remodeler meets: in an existing dwelling unit, service equipment or an enclosed panelboard rated 200 amperes or less may sit where the working-space height is less than 6-1/2 feet.

Electrical Code § 110.26

Open equipment doors may not impede access to or egress from the working space; access is impeded if opened doors leave less than 24 inches wide and 6-1/2 feet high. Three reliefs sit in the same subsection. No working space is required behind or beside a dead-front assembly whose connections and fuses are all reachable from elsewhere, though 30 inches of horizontal space is required at the rear where the back must be opened to work on nonelectrical parts. A smaller space may be allowed by special permission where all exposed live parts are 30 volts rms, 42 volts peak, or 60 volts dc or less. And in an existing building where equipment is being replaced, Condition 2 clearance may be used between dead-front switchboards, switchgear, enclosed panelboards, or motor control centers located across an aisle from each other, where written procedures prohibit opening both sides at once and only authorized qualified persons service them.

Electrical Code § 110.26

Working space about electrical equipment may not be used for storage, and where normally enclosed live parts are exposed for inspection or servicing in a passageway or open space, the working space is guarded. At least one entrance of sufficient area gives access to and egress from the working space. Where equipment containing overcurrent, switching, or control devices is rated 1,200 amperes or more and is over 6 feet wide, or where service disconnecting means grouped under 230.71(B) have a combined rating of 1,200 amperes or more and a combined width over 6 feet, an entrance at least 24 inches wide and 6-1/2 feet high is required at each end of the working space. A single entrance is permitted where the location gives a continuous and unobstructed way of egress, or where the working space is twice the required depth and the distance from the equipment to the nearest edge of the entrance is at least the Table 110.26(A)(1) minimum clear distance for that voltage and condition.

Electrical Code § 110.26

Where equipment rated 800 amperes or more contains overcurrent, switching, or control devices, whatever its width, and a personnel door intended for entrance to and egress from the working space is less than 25 feet from the nearest edge of the working space, that door opens at 90 degrees in the direction of egress and has listed panic hardware or listed fire-exit hardware. Indoor working spaces about service equipment, switchboards, switchgear, enclosed panelboards, and motor control centers are illuminated; automatic controls may not control all of that illumination, and no additional lighting outlet is required where an adjacent light source, or a switched receptacle permitted by 210.70(A)(1), Exception No. 1, already illuminates the space.

Electrical Code § 110.26

Table 110.26(A)(1): at 0 to 150 volts to ground, the minimum clear depth is 3 feet in every condition. At 151 to 600 volts it is 3 feet for Condition 1, 3 feet 6 inches for Condition 2, and 4 feet for Condition 3. Condition 1 is live parts on one side and nothing live or grounded on the other, or live parts on both sides effectively guarded by insulation. Condition 2 is live parts on one side and grounded parts on the other; concrete, brick, and tile walls count as grounded. Condition 3 is exposed live parts on both sides.

Electrical Code § table-110.26-a-1

Terminal connections are tightened to the torque values marked on the equipment or given in the manufacturer's instructions, using an approved means to reach that value, such as a torque tool or a breakaway device with a visual indicator.

Electrical Code § 110.14

Overcurrent protective devices may not be located near easily ignitible material, such as in clothes closets, and may not be located in bathrooms, showering facilities, or locker rooms with showers, other than supplementary overcurrent protection. They may not be located over the steps of a stairway.

Electrical Code § 240.24

Breakers and fused switches must be readily accessible, with the handle's center no more than 6 feet 7 inches above the floor or working platform in its highest position, with exceptions: supplementary overcurrent protection is exempt; so are busway devices and the service and outside-feeder disconnects their own articles cover; a device adjacent to the utilization equipment it supplies may be reached by portable means such as a ladder; and a tool may be used to open listed industrial control panels, hazardous-location enclosures, or environmental enclosures, though the devices inside must still meet the accessibility and 6-foot-7 rules once the enclosure is open.

Electrical Code § 240.24

Where a cable or raceway runs through bored holes in joists, rafters, or other wood members, the edge of the hole stays at least 1-1/4 inches from the edge of the member. Where that distance cannot be kept, the cable or raceway is protected from nails and screws by a steel plate or bushing at least 1/16 inch thick covering the wiring, except that rigid metal conduit, intermediate metal conduit, rigid PVC, RTRC, and EMT need no plate, and a listed and marked thinner plate giving equal or better protection is allowed.

Electrical Code § 300.4