11.3 Securing & Supporting, Plenums, Firestopping & Raceway Installation (Article 300)
Key Takeaways
Under the 2026 NEC 300.13, ceiling grid support wires may not be the only support for wiring above a suspended ceiling unless they are independent support wires installed in addition to the grid wires and distinguishable from them.
Cable ties used to secure and support cables or flexible raceways must be listed and identified for securement and support (2026 NEC 300.13(E)).
No wiring of any type may be installed in ducts used to transport dust, loose stock, or flammable vapors (300.25(A) in the 2026 NEC).
Openings around electrical penetrations through fire-resistance-rated walls, floors, or ceilings must be firestopped by approved methods that maintain the fire resistance rating.
Copper conductors 6 AWG through 1/0 AWG in a vertical raceway need a support at least every 100 ft, and aluminum every 200 ft.
Securing and supporting (300.13, formerly 300.11)
| Rule | Requirement |
|---|---|
| (A) Secured in place | Raceways, cable assemblies, boxes, cabinets, and fittings must be securely fastened in place |
| (B) Above suspended ceilings | Ceiling-support wires that are part of the ceiling grid may not be the only support. Independent support wires added for the electrical work may serve as the sole support if secured at both ends. In fire-rated ceilings they must be distinguishable from the fire-rated design's wires by color, tagging, or other effective means |
| (C) Raceways as support | A raceway may not support other raceways, cables, or nonelectrical equipment, unless it is identified as a means of support, or it supports Class 2 cables that control the equipment the raceway supplies, or boxes as permitted in Article 314 |
| (D) Cables as support | Cables may not be used to support other cables, raceways, or nonelectrical equipment |
| (E) Cable ties (2026) | Cable ties used to secure and support cables, flexible conduit, and flexible tubing must be listed and identified for securement and support; any cable tie fixing device must also be listed. An Informational Note identifies Type 2S and 21S cable ties as evaluated for this use |
Each wiring method article also sets its own support distances, such as within 3 ft of each box and every 10 ft for EMT, or within 12 in. of each box and every 4½ ft for NM cable.
Other Article 300 installation rules
- Damaged wiring (300.4(C), new in 2026): conductors and wiring methods no longer suitable for use because of overheating, fire, corrosion, or water damage must be replaced. Informational Notes point to NEMA GD 1 (water-damaged equipment) and NEMA GD 2 (fire- and heat-damaged equipment).
- Corrosion protection (300.6, 2023 numbering): ferrous raceways, boxes, and fittings must be protected against corrosion by an approved coating. In laundries, canneries, dairy processing, and other indoor wet locations, and where walls are frequently washed, the wiring system must be mounted with at least ¼ in. of airspace from the wall.
- Wet locations above grade (300.11 in the 2026 NEC): the interior of these raceways is a wet location, so conductors must be listed for wet locations. The 2026 NEC adds a requirement for drainage in raceways installed in indoor wet locations.
- Complete raceway systems (300.18, 2023 numbering): raceways must be installed complete between outlet, junction, or splicing points before conductors are installed. Welding to a raceway is not permitted unless it is designed for that use.
- Bends (300.24, new in 2026): the limit of 360 degrees of bends between pull points applies to the whole run, even where it changes from one raceway type to another.
- Induced currents (300.20, 2023 numbering): all conductors of a circuit, including the neutral and EGCs, must be grouped in the same ferrous raceway or enclosure. Where single conductors must pass through ferrous metal separately, slots cut between the holes reduce inductive heating.
Supporting conductors in vertical raceways (300.19, 2023 numbering)
Long vertical runs, such as risers in high-rise buildings, need intermediate support so the weight of the conductors does not pull them from their terminations:
| Conductor size | Aluminum or copper-clad aluminum | Copper |
|---|---|---|
| 18 AWG through 8 AWG | 100 ft | 100 ft |
| 6 AWG through 1/0 AWG | 200 ft | 100 ft |
| 2/0 AWG through 4/0 AWG | 180 ft | 80 ft |
| Over 4/0 AWG through 350 kcmil | 135 ft | 60 ft |
| Over 350 kcmil through 500 kcmil | 120 ft | 50 ft |
| Over 500 kcmil through 750 kcmil | 95 ft | 40 ft |
| Over 750 kcmil | 85 ft | 35 ft |
A support is required at the top of the vertical raceway or as close to the top as practical, plus intermediate supports at these intervals. Approved methods include clamping devices in insulating wedges and junction boxes with insulating supports.
Spread of fire (300.21, 2023 numbering)
Electrical installations in hollow spaces, vertical shafts, and ventilation or air-handling ducts must be made so the possible spread of fire or products of combustion is not substantially increased. Openings around penetrations into or through fire-resistance-rated walls, partitions, floors, or ceilings must be firestopped using approved methods to maintain the fire resistance rating. In practice, use a listed firestop system whose tested design matches the assembly, the penetrating item, and the annular space, and install it exactly per the system listing.
Ducts, plenums, and other air-handling spaces (300.25 in the 2026 NEC, formerly 300.22)
| Space | What is permitted |
|---|---|
| (A) Ducts for dust, loose stock, or vapor removal | No wiring systems of any type |
| (B) Ducts specifically fabricated for environmental air | Type MI cable without an overall nonmetallic covering; Type MC cable with a smooth or corrugated impervious metal sheath without a nonmetallic covering; or EMT, flexible metallic tubing, IMC, or RMC without a nonmetallic covering. Equipment is permitted only if necessary for direct action on, or sensing of, the contained air |
| (C) Other spaces used for environmental air (plenums), such as the space above a suspended ceiling used for return air | Type MI, Type MC, and Type AC cable without nonmetallic coverings; other factory-assembled multiconductor cables listed for use in air-handling spaces; and other cables and conductors installed in EMT, FMT, IMC, RMC, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers |
| (D) Information technology rooms | Article 645 governs |
Nonmetallic cable ties and other nonmetallic accessories used in plenum spaces must be listed as having low smoke and heat release properties. Limited-energy and communications cables in plenums must be plenum rated (for example, CL2P or CMP) under the Chapter 7 cable rules.
Worked example: an office ceiling
A contractor runs MC cable and EMT above a lay-in ceiling used as a return-air plenum in a fire-rated floor-ceiling assembly.
- Support: fasten the EMT and MC cable to the structure, or to independent support wires secured at both ends and tagged or colored to distinguish them from the fire-rated ceiling wires. Do not hang them from the grid wires.
- Plenum wiring: MC cable without a nonmetallic jacket and EMT are both permitted in the plenum. Any PVC-jacketed MC is not.
- Cable ties: if ties secure the MC cable, they must be listed and identified for securement and support, and nonmetallic ties must also be listed for low smoke and heat release.
- Penetrations: where the EMT passes through the rated floor above, seal the opening with a listed firestop system.
Branch-circuit MC cable is installed above a suspended ceiling. Which support method meets the 2026 NEC 300.13(B)?
Tie-wrapping the cable to the ceiling grid's own support wires every 4 ft
Securing it to independent, identified support wires fastened at both ends
Laying the cable on top of the ceiling tiles
Fastening the cable to the sprinkler piping with listed clips
Which wiring method is permitted in a duct specifically fabricated to transport environmental air?
Type NM cable with an overall PVC jacket
Schedule 80 PVC conduit with glued joints
Type AC cable with a PVC jacket
EMT without an overall nonmetallic covering
How far apart may supports be for 4/0 AWG copper conductors in a vertical raceway?
35 ft
60 ft
80 ft
180 ft
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