What is LFNC (Liquidtight Flexible Nonmetallic Conduit)?
LFNC is liquidtight flexible nonmetallic conduit (Types A, B, C) for wet, oily, and outdoor flexible connections, governed by NEC Article 356.
LFNC (Liquidtight Flexible Nonmetallic Conduit) is a flexible plastic raceway with an outer jacket sealed against liquids, oils, and sunlight. NEC Article 356 lists three types — A, B, and C — each with a different inner construction. LFNC handles outdoor equipment connections, food and dairy washdown areas, rooftop HVAC drops, and other places where flexibility plus a liquidtight seal is needed but a metallic raceway would corrode.
The three LFNC types
| Type | Construction | Common use |
|---|---|---|
| LFNC-A | Smooth-bore inner core, reinforcement layer, smooth outer jacket | Outdoor equipment, irrigation controls |
| LFNC-B | Integral reinforcement molded into the wall (most common) | General-purpose, direct burial when listed |
| LFNC-C | Corrugated inner and outer surface | Tight bends, light-duty cord-and-plug runs |
Type B (often branded as Carflex or similar) is by far the most common on commercial and industrial jobs.
Interior cross-section (NEC Chapter 9 Table 4)
| Trade size | LFNC-B area in² |
|---|---|
| 3/8" | 0.192 |
| 1/2" | 0.314 |
| 3/4" | 0.541 |
| 1" | 0.873 |
| 1-1/4" | 1.528 |
| 1-1/2" | 1.981 |
| 2" | 3.246 |
Types A and C have slightly different interior dimensions — check the specific Chapter 9 Table 4 column. Apply NEC Chapter 9 Table 1 fill percentages on the flex conduit fill chart.
NEC code reference (Article 356)
- NEC 356.10 — permitted uses: flexibility needed, protection from liquids/vapors/solids, outdoor where listed and marked sunlight-resistant, direct burial where so listed, and other specific applications
- NEC 356.12 — not permitted where subject to physical damage, where ambient or operating temperature exceeds the conduit's listing, in lengths over 6 ft (except as permitted), or in Class I locations except as covered by NEC 501.10(B)
- NEC 356.20 — trade sizes 3/8" through 4"
- NEC 356.22 — fill per Chapter 9 Table 1
- NEC 356.60 — separate EGC required when used as a flexible connection; LFNC itself is never an EGC
Common applications
- Rooftop HVAC unit final connections
- Outdoor disconnect and motor whips
- Wastewater treatment and food processing washdown
- Irrigation controllers and well-pump panels
- Sunlight-exposed outdoor wiring drops
- Hot tub, pool, and spa equipment pads (with proper listing)
Trade-offs vs LFMC and FMC
| Property | LFNC | LFMC | FMC |
|---|---|---|---|
| Article | NEC 356 | NEC 350 | NEC 348 |
| Core | All plastic | Steel core + PVC jacket | Bare steel only |
| Wet locations | Yes | Yes | No |
| Oil/chemical | Excellent | Good | Poor |
| EGC qualifier | No (separate EGC) | Limited per 250.118(6) | Limited per 250.118(5) |
| Sunlight resistance | Type listed | Yes | Limited |
The big advantage of LFNC over LFMC is complete immunity to corrosion — no steel to rust. The disadvantage is that you must always pull a separate equipment grounding conductor, since plastic cannot carry fault current.
Quick reference
- Article: NEC 356
- Types: A, B, C (B most common)
- Wet locations: yes
- Sunlight: type-listed
- EGC qualifier: no — always pull separate EGC