NEC 400-427, 455-480 — Electrical Equipment (Washington)

NEC 400-427, 455-480 — Electrical Equipment (Washington Journeyman)

Learning Objectives

1.1 Flexible Cords and Cables (Article 400)

400.4 requires cords and cables to conform to the description in Table 400.4. 400.5(A) supplies ampacity through Table 400.5(A)(1) in general and Table 400.5(A)(2) for not more than three current-carrying conductors. In ambient temperatures other than 30°C (86°F), apply the Table 310.15(B)(1)(1) factors matching the cord's temperature rating, and 105°C cords use the 90°C column. Above three current-carrying conductors, reduce from the three-conductor rating per Table 400.5(A)(3).

A neutral carrying only its own circuit's unbalanced current is not counted, but the common conductor of a 3-wire circuit made up of two phase conductors and the neutral of a 4-wire, 3-phase, wye-connected system is a current-carrying conductor, and so is the neutral of a 4-wire, 3-phase wye circuit whose major portion of load is nonlinear (the keys say more than 50 percent), where harmonic currents flow in the neutral.

400.6(A) requires a printed tag attached to the coil, reel, or carton carrying the 310.8(A) information — maximum rated voltage, type letters, manufacturer's identification, and AWG size or circular mil area — plus durable surface marking at intervals not exceeding 610 mm (24 in.) with type designation, size, and number of conductors, and the maximum operating temperature.

1.2 Fixture Wires (Article 402)

Fixture wire ampacity comes from Table 402.5, never from the general conductor tables:

402.6 sets the floor at 18 AWG solid or stranded copper or 16 AWG solid copper-clad aluminum, so 20 AWG is below the minimum size. Type letters carry the temperature limit: 75°C and 90°C for FFH-2 and FFHH-2, 150°C for the ECTFE types HF and HFF. 402.10 permits fixture wire in luminaires where enclosed or protected and not subject to bending or twisting in use, and for connecting luminaires to their branch-circuit conductors. 402.12 forbids the rest: fixture wires shall not be used as branch-circuit conductors except as permitted elsewhere in the Code, so they never serve as service-entrance conductors, feeders, grounding electrode conductors, or branch-circuit conductors feeding receptacles. Protection follows 402.14 and 240.5, holding a 14 AWG fixture wire at its 17-ampere listing.

1.3 Switches and Circuit Breakers (Article 404)

404.6 governs damp and wet locations: surface-mounted switches or circuit breakers shall be enclosed in weatherproof enclosures or cabinets that comply with 312.4, and flush-mounted switches are equipped with weatherproof covers.

404.8(A) requires single-throw knife switches to be placed so that gravity will not tend to close them; a switch approved for the inverted position must have an integral mechanical means to keep the blades open when set. 404.9 requires general-use and motor-circuit switches, circuit breakers, and molded-case switches mounted in an enclosure as described in 404.5 to indicate, where visible when accessing the external operating means, whether they are open (off) or closed (on), and where the handles are operated vertically rather than rotationally or horizontally the up position of the handle shall be the closed (on) position. 404.10 keeps switches readily accessible and 404.20 requires current, voltage, and horsepower markings.

1.4 Wiring Devices and Receptacles (Article 406)

406.11(A) requires receptacles to be marked with the manufacturer's name or identification and voltage and ampere ratings; 406.11(B) sets the floor at not less than 15 amperes, 125 volts, or 15 amperes, 250 volts, of a type not suitable for use as lampholders. 406.11(C) identifies the isolated ground receptacle — one incorporating an isolated equipment grounding conductor connection as permitted in 250.146(D) — by an orange triangle located on the face of the receptacle. 406.11(D) requires nonlocking-type, 125-volt, 15- and 20-ampere controlled receptacles to be permanently marked with the symbol of Figure 406.11(D) and the word "controlled," on the receptacle face and visible after installation. 406.11(E) requires a 125-volt, 15- or 20-ampere receptacle that additionally provides Class 2 power to be listed and built so that the Class 2 circuitry is integral with the receptacle.

Terminations sit in 406.10: unmarked devices may terminate copper or copper-clad aluminum but never aluminum, and wiring devices with screwless push-in terminals shall be installed on not greater than 15-ampere branch circuits and connected with 14 AWG solid copper conductors only. The bank prints that rule as _406.11(3)_; the 2026 edition states it in 406.10(3). 406.12(A) requires receptacles on 15- and 20-ampere branch circuits to be of the grounding type, except as provided in 406.12(D) for non-grounding, tamper-resistant, weather-resistant, and controlled replacements; 406.12(B) and 406.12(C) connect equipment grounding conductor contacts to equipment grounding conductors in accordance with 250.146.

1.5 Panelboards, Switchboards, and Switchgear (Article 408)

408.36 requires a panelboard to be protected by an OCPD rated not greater than the panelboard, within or on the supply side. Part (C) forbids connecting a 3-phase disconnect or OCPD to the bus of any panelboard having less than 3-phase buses and forbids delta breakers in panelboards. Part (D) requires a backfed plug-in-type OCPD or main lug assembly to be secured by an additional fastener that requires other than a pull to release the device. 408.37 sends panelboards in damp or wet locations to 312.4, and neither 404.6 (switches) nor 314.16 (box fill) answers a panelboard question. 408.38 requires dead-front construction, and where the available fault current is greater than 10,000 amperes the panelboard and enclosure combination shall be evaluated for the application. 408.39 requires fuses of any type in panelboards to be installed on the load side of any switches, with service equipment fuses permitted by 230.94 allowed on the line side of the service switch. 408.52 caps instrument and potential-transformer circuits at standard OCPDs of 15 amperes or less.

408.54 is a counting exercise: a panelboard shall have physical means to prevent installing more OCPDs than the number for which it was designed, rated, and listed, and a 2-pole circuit breaker or fusible switch counts as two OCPDs, a 3-pole as three. 408.55(A) sizes top and bottom wire-bending space per Table 312.9(B)(2), Exception No. 1 permitting either space per Table 312.9(A) for a panelboard rated 225 amperes or less containing not over 42 OCPDs. 312.9 sets gutter width where conductors are deflected, and 314.16 is box fill under Table 314.16(B).

1.6 Luminaires (Article 410)

410.10(A) requires luminaires in wet or damp locations to be installed so water cannot enter or accumulate in wiring compartments, lampholders, or other electrical parts: wet locations take luminaires marked suitable for wet locations, damp locations those marked suitable for wet or damp locations.

410.16 governs clothes closets. Part (A) sets the storage space as the volume bounded by the walls and planes from the floor up to 1.8 m (6 ft) or the highest clothes-hanging rod, parallel to the walls at 600 mm (24 in.), then to the ceiling at 300 mm (12 in.) or the shelf width, whichever is greater. Part (B) permits only surface-mounted or recessed incandescent or LED luminaires with completely enclosed light sources, and surface-mounted or recessed fluorescent luminaires. Part (C) excludes open or partially enclosed lamps and pendants. Part (D) sets clearances: 300 mm (12 in.) for surface-mounted incandescent or LED luminaires with a completely enclosed light source, and 150 mm (6 in.) for surface-mounted fluorescent or recessed luminaires.

410.36 governs support. Part (A) permits support from outlet boxes or fittings installed as required by 314.23 and complying with 314.27(A)(1) and 314.27(A)(2), which requires a luminaire over 23 kg (50 lb) to be supported independently of the outlet box unless the box is listed for not less than the weight to be supported. Part (B) requires framing members of suspended ceiling systems used to support luminaires to be securely fastened to each other and to the building structure, with the luminaire fastened by mechanical means such as bolts, screws, or rivets or by listed clips; where the grid is not identified as a support, the answer is independent support wires tied to the building structure as described in 300.11(B)(2), installed in addition to the grid support wires and secured at both ends.

1.7 Appliances and Fixed Electric Heating (Articles 422, 424, 426, 427)

422.11(E) covers a single non-motor-operated appliance: overcurrent protection shall not exceed the rating marked on the appliance, shall not exceed 20 amperes where the rating is unmarked and the appliance is rated 13.3 amperes or less, and shall not exceed 150 percent of the appliance rated current where the appliance is rated over 13.3 amperes. A 12-ampere appliance is therefore served from a 15-ampere branch circuit. 422.10 sets branch-circuit ratings at 125 percent of the marked rating for a continuous-load appliance unless the device and assembly are listed for 100 percent continuous loading. 422.16(B) permits cord-and-plug connection for in-sink waste disposers with a cord of 450 mm (18 in.) to 900 mm (36 in.), for built-in dishwashers and trash compactors with cords of 0.9 m (3 ft) to 1.2 m (4 ft) for compactors or 2.0 m (6.5 ft) for dishwashers, and for wall-mounted ovens, counter-mounted cooking units, and range hoods. A central heating furnace and a fixed electric space heater take permanent wiring. Household cooking appliances take a receptacle sized by the branch circuit under 210.21(B)(1): a range on a 50-ampere circuit takes a 50-ampere receptacle and cord-and-plug connection.

Article 424 lists heating equipment under 424.2, governs reconditioned equipment (424.3), caps branch circuits supplying two or more fixed electric space-heating outlets at 30 amperes and permits fixed infrared heating equipment in other than dwelling units on circuits rated not over 50 amperes (424.4), and states that fixed electric space-heating equipment and any associated motors shall be considered a continuous load (424.5). Continuous means 125 percent: a 3,000-watt, 240-volt heater drawing _12.5_ amperes needs an ampacity of not less than _15.625_, rounded to _15.6_ amperes, and a 10 kW, 240-volt unit drawing _41.67_ amperes needs not less than _52.08_ amperes, landing on the next standard rating of 60 amperes. Conductor size then comes from Table 310.16, where 10 AWG copper at 75°C carries 35 amperes and 12 AWG at 75°C carries 25 amperes. The bank labels the continuous-load rule _424.3(B)_; it is stated in 424.5, and the bank's heating cable item labelled _424.9_ points at the listing requirement of 424.2 with the installation rules in 424.11 through 424.13, so heating cable must be listed for the application and installed per the manufacturer's instructions, not restricted to concrete slabs. 426.4 treats fixed outdoor deicing and snow-melting equipment as a continuous load, and 427.4 governs branch-circuit sizing for heating equipment for pipelines, vessels, and trace heating.

1.8 Phase Converters and Capacitors (Articles 455 and 460)

455.1 states the scope of Article 455, and Article 100 defines a phase converter as a device that converts single-phase power to 3-phase electric power. 455.4 requires a permanent nameplate giving the manufacturer's name, rated input and output voltages, frequency, rated single-phase input full-load amperes, and single-load and total-load kVA or horsepower ratings. 455.6(A)(1) requires single-phase supply conductors with an ampacity of not less than 125 percent of the nameplate single-phase input full-load amperes for variable loads, 455.6(A)(2) giving the fixed-load alternative of 250 percent of the 3-phase motor full-load currents plus other loads; 455.6(B) requires the manufactured phase conductors to be distinctively marked at all accessible locations. 455.7 applies overcurrent protection at not more than 125 percent of the nameplate single-phase input full-load amperes, and 455.8 requires a disconnecting means that simultaneously disconnects all ungrounded single-phase supply conductors, readily accessible and in sight from the converter per 455.8(A), rated not less than 115 percent of the maximum single-phase input full-load amperes per 455.8(C). A 10 kVA converter on a 480-volt input draws _20.83_ amperes and 125 percent is _26.04_ amperes; the same unit on a 240-volt input draws _41.67_ amperes and 125 percent is _52.08_ amperes. The bank's listing and location items carry the older labels _455.2_.

Article 460 covers capacitors. 460.4(A) requires capacitors with more than 11 L (3 gal) of flammable liquid to be vaulted or fenced outdoors per Article 110 Part III. 460.6 requires a means of discharging stored energy and, at 1000 volts or less, reduces the residual voltage to 50 volts, nominal, or less within 1 minute after disconnection. 460.8 requires capacitor conductors with an ampacity of not less than 135 percent of the rated current of the capacitor; 460.9 requires an OCPD in each ungrounded conductor for each bank; and 460.10 requires a disconnecting means in each ungrounded conductor that opens all of them simultaneously and is rated not less than 135 percent of the capacitor rated current. A capacitor item labeled _460.2_ points at the enclosing-and-guarding text now printed as 460.4, and working space at a 480-volt capacitor bank is the general rule of 110.26(A)(1): 900 mm (3 ft) under Condition 1, 1.0 m (3 ft 6 in.) under Condition 2, and 1.2 m (4 ft) under Condition 3 for 151–600 volts to ground.

1.9 Resistors, Reactors, and Stationary Batteries (Articles 470 and 480)

470.1 covers separate resistors and reactors, reconditioned reactors being permitted and reconditioned resistors prohibited (470.3). 470.10 requires them not to be placed where exposed to physical damage, 470.11 requires a thermal barrier where the space between the resistors or reactors and any combustible material is less than 305 mm (12 in.), and 470.12 requires insulated conductors between resistance elements and controllers to be suitable for not less than 90°C. A resistor item labeled _470.2_ refers to the location rule now stated in 470.10.

Article 480 covers stationary batteries with a capacity greater than 3.6 MJ (1 kWh) (480.1). 480.2 requires stationary batteries and battery management equipment to be listed, excepting vented lead-acid and nickel-cadmium types, and 480.7 requires dc disconnecting means for ungrounded conductors from a battery over 60 volts dc. 480.9 requires the structure supporting a battery with corrosive electrolyte to resist deterioration, using nonconducting support members or continuous insulating material. The clearance the bank keys as a 480.9 item, 6 inches (150 mm) between a storage battery and combustible material, belongs to the battery location rules now stated in 480.10.

Under 480.10(A), provisions appropriate to the battery technology shall be made for sufficient diffusion and ventilation of gases from the battery, if present, to prevent the accumulation of an explosive mixture — a performance rule tied to the technology. 480.10(C) requires spaces about stationary batteries to comply with 110.26 and 110.34, measured from the edge of the cabinet, rack, or tray, with 25 mm (1 in.) between a cell container and a wall not requiring servicing access. 480.11 requires a flame arrester on each vented cell and a pressure-release vent on sealed cells that could accumulate excessive internal pressure.

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Summary

Articles 400 through 427 and 455 through 480 govern equipment rather than premises wiring methods, and each follows one pattern: scope, listing, ratings, installation rules, and a few numbers worth memorizing. Article 400 controls cords and cables through Table 400.4 types, the ampacity tables of 400.5(A), the reduction of Table 400.5(A)(3), ambient correction through Table 310.15(B)(1)(1) with 105°C cords on the 90°C column, and the 400.6(A) tag of 310.8(A) information with 610 mm (24 in.) surface marking. Article 402 keeps fixture wire small and purpose-built, with Table 402.5 ampacities, an 18 AWG copper minimum, permitted uses in 402.10, and a prohibition on branch-circuit use in 402.12.

Articles 404 and 406 cover switches, devices, and receptacles: 404.6 for damp and wet locations with 312.4 weatherproof enclosures, 404.8(A) for gravity-open knife switches, 404.9 for open and closed indication with the up position closed on vertical handles, 406.10 for terminations, 406.11 for marking, rating, isolated ground identification, controlled receptacles and integral Class 2 circuitry, and 406.12 for grounding-type installation. Article 408 governs panelboards: the supply OCPD may not exceed the panelboard rating, damp panels comply with 312.4, enclosures are dead-front with the combination evaluated above 10,000 amperes, fuses stay on the load side of switches except under 230.94, instrument circuits are protected at 15 amperes or less, OCPDs are counted with 2-pole and 3-pole devices counting as two and three, and wire-bending space follows Table 312.9(B)(2). Article 410 places luminaires under 410.10(A), limits clothes closet fixtures under 410.16 with 300 mm (12 in.) or 150 mm (6 in.) clearances, and requires support per 410.36 with 314.27(A)(2) governing luminaires over 23 kg (50 lb). Articles 422 and 424 supply the everyday arithmetic — 422.11(E) protection for a single appliance, 422.16(B) cord-and-plug provisions, and the 125 percent continuous-load rule of 424.5 — while Articles 455 through 480 carry their own percentages: 125 percent conductors and 115 percent disconnect for phase converters, 135 percent for capacitor conductors and disconnects with discharge to 50 volts or less in 1 minute, a 305 mm (12 in.) thermal barrier and 90°C insulation for resistors and reactors, and ventilation, spacing, and flame arresters for batteries over 3.6 MJ (1 kWh).