Flexible conduit is a bendable metal or plastic raceway that routes and protects electrical wires while allowing movement and turns.
For the full breakdown, see our best 2″ Flexible Conduit guide.
Flexible conduit is a protective tube used to route and shield electrical wires, cables, and other conductors. Unlike rigid pipe, it bends around obstacles, absorbs vibration from machinery, and fits into tight spaces where a straight run is impossible. Whether you’re connecting a water heater, wiring a motor, or running cable through an irregular pathway, this type of raceway keeps conductors safe from mechanical damage while staying easy to install.
How Flexible Conduit Is Made
Most flexible metallic conduit starts as a flat strip of steel or aluminum that gets helically wound into an interlocking tube. That spiral construction gives the conduit its signature bendability without sacrificing crush resistance. The result is a round cross-section with high mechanical strength that still flexes freely.
ElectriFlex’s product documentation describes the inner core as a helically formed strip of corrosion-resistant steel, which explains why these raceways hold up in demanding environments.
You’ll also find non-metallic options made from polymers, some of which add a liquid-tight jacket for wet locations or chemical resistance. Each type exists to solve a specific installation problem.
Where Flexible Conduit Is Used
Flexible conduit handles jobs rigid pipe can’t. Common applications include:
- Tight spaces and hard turns where bending rigid conduit is impractical
- Connections to vibrating machinery that would shake rigid fittings loose
- Motor leads and listed assemblies in flexible metal raceway systems
- Water-heater and fixture connections in enclosed areas
- Communication cables and power feeds that must navigate irregular pathways
The older trade name “Greenfield” still pops up for the spirally wrapped metal band design.
Product families vary widely — from basic metal types to liquid-tight, abrasion-resistant, and solvent-resistant versions. Selection depends entirely on the environment the conduit will live in.
How To Size Flexible Conduit Correctly
Size selection comes down to conductor count, conductor size, and allowable fill — never just the length of the run. ABB’s engineering datasheet lays out a clear 4-step process for sizing flexible non-metallic conduit:
- Establish the number and size of each wire you’ll run
- Use the CSA chart to find each wire’s cross-sectional area
- Add all the CSA values together
- Pick a conduit with a 40% fill value higher than that total
Pack too many conductors in and you risk overheating and damaging wires during pulls. Manufacturers publish fill charts for exactly this reason.
| Example Size (Electroline EF Type) | Metric Spec |
|---|---|
| Trade size | 1/2″ |
| Inside diameter | 15.70–16.30 mm |
| Outside diameter | 20.80–21.30 mm |
| PVC jacket thickness | 1.00–1.35 mm |
| Minimum bending radius | 70–100 mm |
| Roll length | 30 m |
That minimum bending radius is a hard limit. Over-bending flexible conduit can kink the inner core and restrict wire movement or damage conductors during installation. When fittings and accessories are needed, stick with the same conduit system where possible — dimensions differ by trade size and manufacturer.
For a practical look at specific products and what works for different jobs, this roundup of top flexible conduit options covers tested picks for common installations.
Common Mistakes To Avoid
Flexible conduit gets confused with other products more often than you’d think. Here’s where people go wrong:
- Treating it like fluid hose. Flexible conduit protects electrical wires. Flexible hose carries fluids, gas, or air. They are not interchangeable.
- Assuming all types are liquid-tight. Only specific product families carry liquid-tight ratings. Many are general-purpose or indoor-only.
- Skipping the fill calculation. The 40% threshold exists for safety. Ignoring it causes overheated wires and difficult pulls.
- Treating it like rigid conduit. Flexibility, bend radius, and fitting compatibility vary by type. Always verify the specific rating before purchasing.
Match the conduit to the environmental demands. Need water resistance? Look for a liquid-tight jacket. Chemical exposure? Check solvent resistance. Vibration? Make sure the flexibility rating handles the movement. The right product exists for each scenario.
Flexible conduit earns its place whenever rigid pipe won’t work. Knowing what you’re buying — and what fill limit applies — keeps every installation code-compliant and safe.
FAQs
Is flexible conduit rated for outdoor use?
Only specific types carry outdoor or wet-location ratings. Liquid-tight flexible metallic conduit (LFMC) handles damp environments, but standard flexible metal conduit is often indoor-only. Check the product’s specific rating before installing it outside.
Can flexible conduit be buried directly in the ground?
Most flexible conduit is not rated for direct burial. It lacks the crush resistance and moisture protection that underground-rated rigid conduit provides. For buried runs, use conduit specifically approved for direct earth burial.
What happens if too many wires go in one conduit?
The fill chart calculation prevents both issues before installation starts.
References & Sources
- ElectriFlex. “ElectriFlex EF Flexible Conduit Product Sheet.” Describes the helically formed corrosion-resistant steel core construction.
- ABB/Thomas & Betts. “Flexible Conduit Systems Catalogue.” Documents the 4-step CSA sizing process and 40% fill requirement.
- RS Components. “Liquid-tight Flexible Steel Conduit Datasheet.” Lists specific dimensions, bending radii, and product code information.