12.2 Flexible Conduits, ENT, Wireways, Auxiliary Gutters & Surface Raceways
Key Takeaways
FMC and LFMC must be secured within 12 in. of each box or fitting and at intervals not exceeding 4½ ft, with exceptions for fished runs and short lengths at terminals where flexibility is needed (348.30 and 350.30).
ENT is permitted exposed or concealed in buildings of three floors or less above grade, and concealed behind a 15-minute finish rating in taller buildings (362.10).
Conductors in a metal wireway may not fill more than 20% of its interior cross-sectional area, and splices and taps may not fill more than 75% at any point (376.22 and 376.56).
Ampacity adjustment factors apply to wireways and auxiliary gutters only when more than 30 current-carrying conductors are present at any cross section (376.22(B) and 366.23).
Metal wireways must be supported at intervals not exceeding 5 ft horizontally and 15 ft vertically (376.30).
Flexible raceways
| Wiring method | Article | Key uses and limits | Securing and supporting |
|---|---|---|---|
| Flexible metal conduit (FMC) | 348 | Dry locations; not in wet locations, hoistways (with exceptions), storage battery rooms, hazardous locations (except as permitted), underground, embedded in concrete, or where subject to physical damage; minimum trade size ½ (⅜ in specific cases, such as luminaire and motor whips not over 6 ft) | Within 12 in. of each box and every 4½ ft |
| Liquidtight flexible metal conduit (LFMC) | 350 | Where flexibility or protection from liquids, vapors, or solids is needed; direct burial where listed and marked; not where subject to physical damage | Within 12 in. and every 4½ ft |
| Liquidtight flexible nonmetallic conduit (LFNC) | 356 | Where flexibility and liquidtight protection are needed; outdoors and direct burial where listed and marked; not where subject to physical damage or above its temperature rating | Within 12 in. of each box and every 3 ft |
| Flexible metallic tubing (FMT) | 360 | Dry locations, concealed or accessible, branch circuits; trade sizes ⅜ to ¾ | Per its listing and Article 360 |
Common exceptions to support: fished runs; lengths of not more than 3 ft at terminals where flexibility is necessary; and lengths of not more than 6 ft from the last support to a luminaire or other equipment within an accessible ceiling. Listed fittings may count as a means of securement.
Bends: the total of bends between pull points may not exceed 360 degrees (and the 2026 NEC 300.24 applies that limit across transitions between raceway types).
Grounding: FMC and LFMC may serve as the EGC only within the limits of 250.118: fittings listed for grounding, 6 ft maximum total flexible length in the ground return path, circuits of 20 A or less (FMC and ⅜–½ LFMC) or 60 A or less (¾–1¼ LFMC), trade size not over 1¼, and not where flexibility after installation is required. Otherwise run a wire-type EGC. LFNC is nonmetallic and always needs an EGC.
Electrical nonmetallic tubing (ENT, Article 362)
ENT is a pliable, corrugated raceway that can be bent by hand.
| Rule | Requirement |
|---|---|
| Buildings three floors or less above grade | Exposed or concealed |
| Buildings over three floors | Concealed in walls, floors, and ceilings that provide a thermal barrier with at least a 15-minute finish rating |
| Concrete | Embedded in concrete slabs or poured concrete, with fittings identified for the purpose |
| Wet locations | Indoors, and in concrete slabs on or below grade, with fittings identified for the purpose |
| Not permitted | Hazardous (classified) locations, except as permitted elsewhere; as support for luminaires and other equipment; ambient temperatures above its rating; direct burial; exposed in theaters and places of assembly, except as permitted; exposed to direct sunlight unless identified as sunlight resistant |
| Support (362.30) | Within 3 ft of each box and every 3 ft |
Wireways (Articles 376 and 378) and auxiliary gutters (Article 366)
A wireway is a sheet-metal or nonmetallic trough with a hinged or removable cover, used to house and protect conductors laid in after the wireway is installed. An auxiliary gutter supplements the wiring space at switchboards, meter centers, distribution centers, and similar equipment, and may not extend more than 30 ft beyond the equipment it supplements.
| Rule | Metal wireway (376) | Auxiliary gutter (366) |
|---|---|---|
| Conductor fill | 20% of interior cross-sectional area | 20% |
| Splices and taps | Conductors, splices, and taps not over 75% of the area at that point | 75% |
| Ampacity adjustment | Table 310.15(C)(1) factors apply only where more than 30 current-carrying conductors are at any cross section | Same 30-conductor rule |
| Support | Horizontal: at each end or joint (unless listed otherwise) and every 5 ft; vertical: every 15 ft, with not more than one joint between supports | Sheet-metal gutters every 5 ft |
| Bending space | Where conductors are deflected, Table 312.6(A) applies | Same |
Wireways may not be used where subject to severe physical damage, and nonmetallic wireways (Article 378) have their own temperature and sunlight limits.
Surface raceways (Articles 386 and 388)
Surface metal raceways are permitted in dry locations and in Class I, Division 2 locations as permitted by Article 501; they are not permitted where subject to severe physical damage, where voltage exceeds 300 V between conductors (unless the metal is at least 0.040 in. thick), in hoistways, or where concealed (with limited exceptions). The number of conductors may not exceed the number the raceway is designed for. Ampacity adjustment is not required in surface metal raceways when all of these are true: the cross-sectional area exceeds 4 in², there are not more than 30 current-carrying conductors, and fill does not exceed 20%.
Worked example: wireway fill
A 4 in. × 4 in. metal wireway has an interior cross section of 16 in².
- Maximum conductor fill: in².
- Maximum fill at a splice point: in².
- 500 kcmil THHN has an area of 0.7073 in² (Chapter 9, Table 5). The wireway can hold , so 4 conductors of 500 kcmil THHN.
- With 4 current-carrying conductors (not more than 30), no Table 310.15(C)(1) adjustment applies.
What is the maximum spacing between supports for a horizontal run of trade size ½ flexible metal conduit, excluding the permitted exceptions?
4½ ft
3 ft
6 ft
10 ft
A metal wireway contains 36 current-carrying conductors at one cross section. What does 376.22(B) require?
No ampacity adjustment, because wireways are exempt
Apply the Table 310.15(C)(1) adjustment factors
Reduce the conductor fill to 10% of the wireway's cross section
Install a second wireway so neither holds more than 30
A seven-story office building needs branch-circuit raceways in its upper floors. Under 362.10, how may ENT be installed above the third floor?
Exposed anywhere in the building, if it is supported every 3 ft
Only in hazardous locations
Concealed behind a thermal barrier with a 15-minute finish rating
ENT is prohibited above the third floor of any building
Sections you finish are checked off in the contents.