Electrical Nonmetallic Tubing (ENT) is a flexible, corrugated plastic conduit used to protect and route electrical wiring in construction projects. Manufactured from polyvinyl chloride (PVC) or other flame-retardant thermoplastic materials, ENT serves as a pathway for electrical conductors, shielding them from physical damage and environmental factors. It is often recognized by its common nickname, “smurf tube,” due to the bright blue color frequently displayed in installations.
Key Features and Installation Benefits
The corrugated structure allows ENT to be highly flexible and easily bent by hand without specialized tools. This hand-bendable quality speeds up installation by eliminating the need to cut and assemble numerous elbow fittings to navigate obstacles. The tubing’s lightweight nature also contributes to efficiency, making it easier to transport, handle, and secure, especially when working overhead.
ENT’s non-metallic construction provides an advantage in environments where metal conduits would degrade. Because it is plastic, the tubing is resistant to rust and corrosion, making it suitable for damp locations or when embedded in concrete. This resistance ensures the long-term integrity of the electrical pathway. ENT is also generally a more affordable option than metallic conduits for residential and light commercial wiring needs.
Where ENT Conduit is Used and Restricted
ENT is primarily intended for use in concealed locations, such as within the hollow spaces of walls, ceilings, and floors, where it is protected from physical impact. A common application is in concrete slab construction, where the tubing is laid out before the concrete is poured. When installed with specific fittings, ENT is considered “concrete-tight,” ensuring the electrical system remains protected within the slab.
The National Electrical Code (NEC) Article 362 governs the use of ENT and specifies several limitations for safety and compliance. The tubing is generally not permitted in exposed locations where it is subject to physical damage, such as high-traffic areas. Furthermore, its use in buildings exceeding three floors is restricted unless the ENT is concealed within a fire-rated assembly providing a minimum 15-minute thermal barrier. All installations must adhere to local electrical codes.
ENT vs. Traditional Metal Conduit
Comparing ENT with Electrical Metallic Tubing (EMT), a common metal alternative, highlights the trade-offs between the two conduit types. ENT’s flexibility allows for quick installation, but sacrifices mechanical protection. EMT, a rigid, smooth-walled metal tube, offers superior resistance to crushing and impact, making it the preferred choice for exposed runs in high-traffic or industrial environments.
A key difference lies in the electrical grounding requirements for both materials. EMT, due to its metallic composition, can often serve as the equipment grounding conductor if connections are properly bonded. Conversely, ENT is non-conductive, meaning a separate grounding wire must always be pulled inside the tubing along with the power conductors to ensure a safe electrical system. ENT is best suited for concealed, low-impact runs where installation speed and cost are priorities, while EMT is reserved for exposed applications requiring maximum durability.