Raceways & Enclosures

Raceways & Enclosures — Arkansas Master Electrician Exam (2023 NEC)

Learning Objectives

By the end of this chapter, you will be able to:

1.1 Raceway Types and Permitted Uses (Chapter 3)

The NEC classifies raceways as channels designed expressly for holding wires, cables, or busbars. For the master exam, you must know not just what a raceway is, but where each type is permitted and prohibited.

Rigid Metal Conduit (RMC) — Article 344. RMC is the heavy-wall galvanized steel conduit. Permitted in all atmospheric conditions and occupancies, including hazardous locations (Class I, II, III) when threaded. Minimum size is ½ inch. For service conductors, RMC is the gold standard for physical protection.

Intermediate Metal Conduit (IMC) — Article 342. Lighter than RMC but same threading characteristics. Permitted wherever RMC is permitted, except where specific corrosion conditions exist. IMC is a cost-effective alternative for commercial work.

Electrical Metallic Tubing (EMT) — Article 358. Thin-wall, not threaded. Permitted for exposed or concealed work in dry, damp, or wet locations (with corrosion protection). Prohibited in hazardous locations where physical damage is severe, and in the presence of corrosive vapors. EMT is the workhorse for commercial branch circuits and feeders.

Flexible Metal Conduit (FMC) — Article 348. Permitted for the final 6 feet of connection to motors and equipment that vibrate. The equipment grounding conductor must be installed inside if the conduit is used as the sole grounding path and the circuit exceeds 6 feet or the overcurrent device exceeds 20 A for lighting/appliance circuits.

Liquidtight Flexible Metal Conduit (LFMC) — Article 350. Used for wet locations, outdoor equipment, and where oil or coolant is present. The 6-foot rule applies similarly, but LFMC is permitted for longer runs if supported every 4.5 feet.

Rigid PVC Conduit (PVC) — Article 352. Schedule 40 and 80. Permitted for direct burial, concrete encasement, and corrosive environments. Prohibited in hazardous locations (unless listed for that use) and where subject to physical damage. Expansion fittings are required where the length change due to temperature exceeds ¼ inch (Table 352.44).

Electrical Nonmetallic Tubing (ENT) — Article 362. For use in buildings of any height, but not permitted in exposed locations, in plenums (unless listed), or where subject to physical damage. ENT is common for concealed work in residential and light commercial.

Surface Raceways — Article 386 (metal) and 388 (nonmetallic). Used for additions to existing installations. The total cross-sectional area of conductors must not exceed 20% of the raceway interior (for surface raceways with a base and separate cover).

Wireways — Article 376 (metal) and 378 (nonmetallic). These are troughs with hinged or removable covers. Fill is limited to 20 conductors (derating applies beyond 30 conductors per 376.22). Wireways are not raceways for the purpose of the 40% fill rule; they use a different fill calculation based on conductor cross-section area.

Busways — Article 368. Used for high-current feeders (400 A to 5000 A). Overcurrent protection is required at the point where the busway receives its supply, unless the tap rules of 368.17 apply.

1.2 Conduit Fill and Sizing (Chapter 9)

The master must calculate conduit fill correctly — this is a common exam calculation and a frequent field inspection failure.

The 40% Rule (Table 1, Chapter 9). For one conductor, fill is 53% of the interior cross-section. For two conductors, fill is 31%. For three or more conductors, fill is 40%. These percentages apply to the total cross-sectional area of all conductors.

Conductor Area (Table 5, Chapter 9). Use the approximate area in square inches for THHN/THWN-2. For example, a #12 THHN is 0.0133 in², #10 is 0.0211 in², #8 is 0.0366 in², #4 is 0.0973 in², and #1/0 is 0.1855 in². These are for compact-stranded conductors; if you use a different insulation type, use the appropriate column.

Conduit Area (Table 4, Chapter 9). For EMT, the 40% fill area for ¾ inch is 0.213 in², for 1 inch is 0.346 in², for 1¼ inch is 0.598 in², and for 2 inch is 1.342 in².

Calculation Example (for your reference): Three #4 THHN and one #6 ground in 1¼ inch EMT. #4 area = 0.0973 in² × 3 = 0.2919 in². #6 area (Table 5) = 0.0507 in². Total = 0.3426 in². The 40% fill for 1¼ inch EMT is 0.598 in² — this passes. But check the number of conductors for derating: four current-carrying conductors require derating per Table 310.15(C)(1).

Exam Trap: Do not forget that the equipment grounding conductor counts for fill but not for derating. However, neutrals count for derating if they carry unbalanced current (which they do in a 3-phase, 4-wire wye system).

Bends and Pull Points (Articles 344.24, 358.24, etc.). The total of all bends between pull points must not exceed 360°. A pull point (junction box) must be provided if the raceway exceeds 360° of bends. For EMT, the maximum number of quarter bends is four (4 × 90° = 360°). For RMC, the same rule applies.

Raceway Support (Tables 344.30(B), 358.30). EMT must be supported within 3 feet of each outlet box and every 10 feet thereafter. RMC must be supported within 3 feet and every 14 feet (for ½ through 1 inch) or 16 feet (for 1¼ through 2 inch). PVC must be supported every 3 feet and within 3 feet of boxes.

1.3 Enclosures — Sizing and Working Clearance (Article 110)

Enclosures include panelboards, junction boxes, pull boxes, and service equipment. The master must verify that the enclosure is large enough for conductor bending space and that the working space is compliant.

Minimum Working Space (Table 110.26(A)(1)). For equipment operating at 0–150 V to ground, the minimum clear distance is 3 feet. For 151–600 V, the distance depends on the conditions: 3 feet for condition 1 (exposed live parts on one side, grounded on the other), 3.5 feet for condition 2 (exposed live parts on both sides), and 4 feet for condition 3 (exposed live parts on both sides, with a grounded surface on the other). For service equipment rated 1200 A or more, the working space must be at least 6 feet wide (110.26(A)(2)).

Headroom (110.26(A)(3)). The minimum headroom is 6.25 feet (6 feet 3 inches) for equipment operating at 600 V or less. However, if the equipment is a panelboard mounted such that the top is not more than 6.25 feet above the floor, the headroom requirement is waived for that panelboard.

Enclosure Size for Conductors (Article 314). For pull boxes and junction boxes, Table 314.28(A) provides minimum dimensions based on the largest raceway size. For a straight pull, the length of the box must be at least 8 times the trade size of the largest raceway. For an angle pull, the distance to the opposite wall must be at least 6 times the trade size of the largest raceway, plus the sum of the diameters of all other raceways on the same wall.

Example: A junction box with a 2-inch EMT entering on the left and exiting on the right (straight pull) must be at least 16 inches long. If the 2-inch enters on the left and exits on the top (angle pull), the distance from the left wall to the top wall must be at least (6 × 2) + 0 = 12 inches, but you must also check the other dimension.

Exam Trap: For angle pulls, the sum of the diameters of all other raceways on the same wall is added. If you have a 2-inch and a 1-inch raceway on the same wall, the distance is (6 × 2) + 1 = 13 inches.

1.4 Services and Service Equipment (Article 230)

Service conductors and equipment have specific rules that a master must enforce.

Service Disconnect (230.71). For a service with multiple disconnects, the disconnects must be grouped and each must be labeled. The maximum number of service disconnects is six (for services over 600 V, the rule is different — see 230.71(B) for the 2023 change allowing more than six for certain high-voltage services).

Service Overcurrent Protection (230.90). Each ungrounded service conductor must have overcurrent protection. The rating of the service disconnect must not be less than the calculated load per Article 220. The service disconnecting means must have a rating of at least 100 A for a one-family dwelling (230.79(C)).

Service Grounding and Bonding (250.24). The grounded conductor (neutral) must be bonded to the service equipment enclosure and to the grounding electrode conductor. The bonding jumper must be sized per Table 250.102(C)(1) based on the area of the largest ungrounded service conductor.

Service Entrance Conductors (230.42). The minimum size of service entrance conductors must be 100 A for a one-family dwelling, but the ampacity must be sufficient for the calculated load. For 3-phase services, the neutral is sized per 220.61 — it can be reduced if the maximum unbalanced load is known, but it must not be smaller than the grounding electrode conductor required by 250.66.

Exam Trap: For a 3-phase, 4-wire service, the neutral is considered a current-carrying conductor for derating purposes only if it carries the unbalanced current. In a balanced 3-phase load, the neutral carries little or no current, so it may not count for derating — but it always counts for conduit fill.

1.5 Separately Derived Systems (Article 250.30)

Transformers and generators that create a new grounded system are "separately derived systems." The master must ensure proper grounding and bonding.

Grounding Electrode (250.30(A)). The system must be connected to a grounding electrode (building steel, ground ring, or concrete-encased electrode) via a grounding electrode conductor sized per Table 250.66. The conductor must be connected to the grounded conductor (neutral) at the system's grounding electrode conductor terminal.

Bonding (250.30(A)(2)). The grounded conductor must be bonded to the equipment grounding conductor and the enclosure of the transformer or generator. The bonding jumper must be sized per Table 250.102(C)(1).

Impedance Grounding (250.36). For high-impedance grounded systems (used for continuity of service in industrial plants), the grounding impedance is connected between the neutral point and ground. The neutral must be fully insulated, and the system must have a ground detection system.

Generator Transfer Switches (Article 702). For optional standby systems, the transfer switch must be listed and must prevent parallel operation. The generator must have its own grounding electrode if it is a separately derived system (i.e., if the neutral is switched).

1.6 Feeder Sizing and Overcurrent Protection (Articles 215 and 240)

Feeder conductors must have an ampacity of at least the calculated load, and the overcurrent device must protect them.

Feeder Ampacity (215.2). The minimum feeder ampacity is the sum of the noncontinuous load plus 125% of the continuous load. For a 3-phase feeder, the load is calculated using the line-to-line voltage and the square root of 3 (√3 ≈ 1.732).

Example: A 3-phase, 208 V feeder serving 50 A of continuous load and 20 A of noncontinuous load requires an ampacity of (50 × 1.25) + 20 = 82.5 A. The next standard size overcurrent device (per 240.6) is 90 A, and the conductor must have an ampacity of at least 82.5 A — typically #3 THHN (85 A at 75°C) or #2 THHN (95 A at 75°C).

Overcurrent Protection Coordination (240.12). For emergency systems, legally required standby systems, and critical operations power systems (COPS), overcurrent devices must be coordinated so that a fault on a branch circuit does not take out the feeder. This is a selective coordination requirement — the master must ensure that the time-current curves of the upstream and downstream devices do not overlap.

Transformer Secondary Protection (240.21(C)). The secondary conductors of a transformer can be protected by the primary overcurrent device if the primary device is sized at or below 125% of the primary rated current (for transformers with a secondary voltage of 600 V or less). For transformers over 600 V, the primary device must be at or below 250% of the primary current.

1.7 Motor and Generator Applications (Article 430)

Motors are a major part of commercial and industrial work. The master must know the branch-circuit, feeder, and overload rules.

Motor Branch Circuit (430.52). The branch-circuit short-circuit and ground-fault protective device must be sized per Table 430.52. For a standard inverse-time breaker, the maximum is 250% of the motor's full-load current (FLC). For a non-time-delay fuse, the maximum is 300%. If the motor will not start with these settings, the next higher standard size is permitted, but not above 400% for inverse-time breakers.

Motor Overload Protection (430.32). The overload device must be sized at no more than 125% of the motor's full-load current for motors with a service factor of 1.15 or more, or a temperature rise of 40°C or less. For other motors, the maximum is 115%.

Motor Feeder (430.24). The feeder must have an ampacity of at least 125% of the largest motor's FLC plus the sum of the FLCs of all other motors on the feeder.

Motor Disconnect (430.102). A disconnecting means must be located within sight of the motor and the driven machinery. The disconnect must be capable of being locked in the open position.

Generators (Article 445). Generators must have overcurrent protection for the conductors. If the generator is a separately derived system, the neutral must be grounded per 250.30. The generator must have a disconnecting means that is capable of being locked.

1.8 Code Navigation — Quick Reference

1.9 Inspection and Supervision Points

As a master, you are responsible for the work of others. On site, verify the following:

1.10 Common Exam Traps

This chapter covers the core raceway and enclosure rules for the Arkansas Master exam. Always verify the specific article in the 2023 NEC during the open-book exam — the table numbers and section references above are your map, but the code text is the law.