What is ENT (Electrical Nonmetallic Tubing)?
ENT is corrugated blue 'smurf tube' PVC for concealed dry-location wiring, governed by NEC Article 362. Building height limits apply.
ENT (Electrical Nonmetallic Tubing) is a corrugated, pliable polyvinyl chloride raceway commonly nicknamed "smurf tube" for its bright blue color. It snaps to shape by hand, joins with solvent-welded or snap-in couplings, and is the cheapest concealed raceway in residential and light commercial wiring. NEC Article 362 governs ENT, with strict limits on building height and exposed installation.
Construction
- Material: Pliable, corrugated PVC
- Color: Blue (most common), also orange or other manufacturer-specific
- Trade sizes: 1/2" through 2"
- Sold: In coils (typically 100 ft or 250 ft)
- Joining: Solvent cement, push-on snap fittings, or threaded adapters to rigid PVC
The corrugations let the tubing flex around obstacles and through stud bays — installers can route ENT by hand without bending tools, which is its main labor advantage.
Interior cross-section (NEC Chapter 9 Table 4)
| Trade size | Interior area in² |
|---|---|
| 1/2" | 0.285 |
| 3/4" | 0.508 |
| 1" | 0.832 |
| 1-1/4" | 1.453 |
| 1-1/2" | 1.986 |
| 2" | 3.291 |
Same interior values as PVC Schedule 40 in Chapter 9 Table 4 for fill purposes. Run conductor counts on the PVC conduit fill chart or the conduit fill calculator.
NEC code reference (Article 362)
- NEC 362.10 — permitted uses:
- Building of any height where concealed in walls/floors/ceilings with at least 15-minute finish rating
- Buildings exceeding 3 floors above grade, only concealed within fire-rated construction
- Concealed in walls, floors, ceilings of three-floor-or-less buildings
- Exposed where not subject to physical damage
- Severe corrosive influences
- Concealed inside masonry walls with appropriate listing
- Damp locations (not wet) where not subject to physical damage
- Direct above-floor in slab-on-grade construction
- NEC 362.12 — not permitted in any hazardous location (with exceptions), as support for fixtures, in ambient over 50°C, exposed where subject to physical damage, in wet locations unless listed, for direct earth burial
- NEC 362.20 — minimum 1/2", maximum 2"
- NEC 362.22 — fill per Chapter 9 Table 1
- NEC 362.30 — supported within 3 ft of every box and every 3 ft thereafter; concealed runs are supported by their entry points
Common applications
- Residential branch circuits (concealed in framing)
- Concealed wiring in multi-family construction with fire-rated assemblies
- Slab-on-grade installations under poured concrete floors
- Computer room and data center floor distributions
- Tilt-up wall concealed conduit
- Renovation work where flexibility through joists saves drilling
Trade-offs vs rigid PVC
| Property | ENT | PVC Sch 40 |
|---|---|---|
| Article | NEC 362 | NEC 352 |
| Form | Corrugated, pliable | Rigid stick |
| Field bending | Hand-shapes around obstacles | Heat box required |
| Wet locations | No | Yes |
| Direct burial | No | Yes |
| Exposed in tall buildings | Restricted | Permitted |
| Cost per ft | Lowest | Higher |
ENT trades durability and outdoor capability for installation speed. On residential rough-in, it can be roped through studs in less than half the time of rigid PVC.
Quick reference
- Article: NEC 362
- Nickname: smurf tube
- Wet locations: no
- Direct burial: no
- EGC qualifier: no — pull a separate EGC
- Trade sizes: 1/2" through 2"