IMPORTANT
Quick Summary: Under the National Electrical Code (NEC Article 356 and Annex C Table C.5), Liquidtight Flexible Nonmetallic Conduit (LFNC), commonly known as “Carflex” or “Type B Liquidtight”, is an entirely nonmetallic, corrosion-proof flexible raceway ideal for swimming pools, outdoor HVAC whips, and coastal environments. When pulling three or more conductors of the same size (THHN/THWN-2 at 40% fill), the standard capacities are:
- 3/8″ LFNC (Fixture/Motor Whips): 8 wires of 14 AWG | 5 wires of 12 AWG | 3 wires of 10 AWG | 1 wire of 8 AWG
- 1/2″ LFNC: 12 wires of 14 AWG | 9 wires of 12 AWG | 5 wires of 10 AWG | 2 wires of 6 AWG
- 3/4″ LFNC: 22 wires of 14 AWG | 16 wires of 12 AWG | 10 wires of 10 AWG | 4 wires of 6 AWG
- 1″ LFNC: 35 wires of 14 AWG | 26 wires of 12 AWG | 16 wires of 10 AWG | 6 wires of 6 AWG
- 1-1/4″ LFNC: 61 wires of 14 AWG | 45 wires of 12 AWG | 28 wires of 10 AWG | 11 wires of 6 AWG
Key Takeaways
- The 40 Percent Standard (NEC Chapter 9 Table 1): For runs containing three or more conductors, total wire cross-sectional area cannot exceed 40% of the LFNC conduit interior area.
- 100% Corrosion Immunity (NEC Article 356): Because LFNC contains no metal core, it will never rust, corrode, or degrade, making it the #1 choice for chlorine pool pumps, salt water spas, chemical plants, and fertilizer storage.
- Mandatory Equipment Grounding Conductor (NEC 356.60): Unlike metallic conduits, nonmetallic LFNC has zero conductivity. A dedicated green insulated equipment grounding conductor is 100% mandatory inside every LFNC raceway.
- Length Restrictions for Flexibility (NEC 356.12(3)): Where flexibility is required for equipment operation (such as vibrating pumps and motors), LFNC is generally limited to 6 feet (1.8 m) in length unless specially approved.
LFNC Carflex Standards At-A-Glance
NEC Article 356 Liquidtight Flexible Nonmetallic Conduit
Master LFNC Conduit Fill Chart (NEC Annex C Table C.5)
The table below provides the maximum allowable number of conductors for compact copper THHN/THWN-2 conductors inside Liquidtight Flexible Nonmetallic Conduit (Type LFNC-B) from 3/8 inch to 2 inches based on NEC Chapter 9 Table 4 (40% fill limit for 3 or more wires).
| Conductor Size (AWG/kcmil) | Wire Area (sq. in.) | 3/8″ LFNC (0.077 sq. in.) | 1/2″ LFNC (0.125 sq. in.) | 3/4″ LFNC (0.213 sq. in.) | 1″ LFNC (0.340 sq. in.) | 1-1/4″ LFNC (0.598 sq. in.) | 1-1/2″ LFNC (0.779 sq. in.) | 2″ LFNC (1.307 sq. in.) |
|---|---|---|---|---|---|---|---|---|
| 14 AWG THHN | 0.0097 | 8 | 12 | 22 | 35 | 61 | 80 | 134 |
| 12 AWG THHN | 0.0133 | 5 | 9 | 16 | 26 | 45 | 58 | 98 |
| 10 AWG THHN | 0.0211 | 3 | 5 | 10 | 16 | 28 | 37 | 61 |
| 8 AWG THHN | 0.0366 | 1 | 3 | 5 | 9 | 16 | 21 | 35 |
| 6 AWG THHN | 0.0507 | 0 | 2 | 4 | 6 | 11 | 15 | 25 |
| 4 AWG THHN | 0.0824 | 0 | 1 | 2 | 4 | 7 | 9 | 15 |
| 3 AWG THHN | 0.0973 | 0 | 1 | 2 | 3 | 6 | 8 | 13 |
| 2 AWG THHN | 0.1159 | 0 | 1 | 1 | 2 | 5 | 6 | 11 |
| 1 AWG THHN | 0.1339 | 0 | 0 | 1 | 2 | 4 | 5 | 9 |
| 1/0 AWG THHN | 0.1562 | 0 | 0 | 1 | 2 | 3 | 4 | 8 |
| 2/0 AWG THHN | 0.1863 | 0 | 0 | 0 | 1 | 3 | 4 | 7 |
| 3/0 AWG THHN | 0.2223 | 0 | 0 | 0 | 1 | 2 | 3 | 5 |
| 4/0 AWG THHN | 0.2679 | 0 | 0 | 0 | 0 | 2 | 2 | 4 |
| 250 kcmil (MCM) | 0.3970 | 0 | 0 | 0 | 0 | 1 | 1 | 3 |
| 350 kcmil (MCM) | 0.5242 | 0 | 0 | 0 | 0 | 0 | 1 | 2 |
| 500 kcmil (MCM) | 0.7073 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
[!PRO TIP] Custom Spa & Pool Calculations: Sizing custom hot tub whips, AC disconnects, or pool heater feeds? Calculate exact multi-conductor totals instantly with our Interactive Conduit Fill Calculator.
LFNC Dimensions and Internal Area Reference (NEC Table 4)
Type LFNC-B is engineered with a smooth interior wall reinforced by an integral rigid PVC spiral. The table below outlines internal dimensions and legal fill limits across all trade sizes.
| LFNC Trade Size | Internal Diameter (in.) | Total Internal Area (100%) | 1 Wire (53% Fill Limit) | 2 Wires (31% Fill Limit) | 3+ Wires (40% Fill Limit) | 24″ Nipple (60% Fill Limit) |
|---|---|---|---|---|---|---|
| 3/8″ | 0.494 in. | 0.192 sq. in. | 0.102 sq. in. | 0.059 sq. in. | 0.077 sq. in. | 0.115 sq. in. |
| 1/2″ | 0.632 in. | 0.314 sq. in. | 0.166 sq. in. | 0.097 sq. in. | 0.125 sq. in. | 0.188 sq. in. |
| 3/4″ | 0.824 in. | 0.533 sq. in. | 0.283 sq. in. | 0.165 sq. in. | 0.213 sq. in. | 0.320 sq. in. |
| 1″ | 1.041 in. | 0.851 sq. in. | 0.451 sq. in. | 0.264 sq. in. | 0.340 sq. in. | 0.511 sq. in. |
| 1-1/4″ | 1.380 in. | 1.496 sq. in. | 0.793 sq. in. | 0.464 sq. in. | 0.598 sq. in. | 0.898 sq. in. |
| 1-1/2″ | 1.575 in. | 1.948 sq. in. | 1.033 sq. in. | 0.604 sq. in. | 0.779 sq. in. | 1.169 sq. in. |
| 2″ | 2.040 in. | 3.269 sq. in. | 1.732 sq. in. | 1.013 sq. in. | 1.307 sq. in. | 1.961 sq. in. |
Because LFNC is 100% nonmetallic, an equipment grounding conductor must always be pulled through the conduit to bond equipment. When calculating conduit fill, always include the green equipment grounding conductor in your total wire area calculation.
Important NEC Installation Rules for LFNC Conduit
When designing and installing Liquidtight Flexible Nonmetallic Conduit systems, keep these code requirements in mind:
- Permitted Applications (NEC 356.10): LFNC is permitted in exposed and concealed locations, outdoor sunlight-exposed runs, direct burial in earth (where marked), and corrosive environments such as pool pads and wastewater facilities.
- Approved Nonmetallic Fittings (NEC 356.42): Only listed liquidtight nonmetallic fittings (such as Carlon Carflex push-on or screw-in compression fittings) are permitted to maintain liquidtight integrity.
- Support Intervals (NEC 356.30): LFNC must be securely fastened within 12 inches of each box or termination and supported at intervals not exceeding 3 feet (900 mm). Exceptions apply for whips up to 6 feet in length connecting motors or pool equipment.
- Bend Limits (NEC 356.26): Total bends between pull points cannot exceed 360 degrees. Review our 360-degree conduit bend limit guide to avoid pinching the flexible nonmetallic wall.
Frequently Asked Questions (FAQs)
LFMC (Sealtite) has an internal interlocked steel core with an outer PVC jacket. LFNC (Carflex) is 100% nonmetallic with an integral rigid PVC spiral, making it lighter, completely rust-proof, and easier to cut.
Under NEC Annex C Table C.5, you can install up to 5 conductors of 10 AWG THHN/THWN-2 in 1/2-inch LFNC conduit under the 40% fill limit.
A standard 50-amp hot tub using three 6 AWG copper conductors plus one 8 AWG insulated ground wire (0.1887 sq. in. total) requires a minimum 3/4-inch LFNC conduit (0.213 sq. in. capacity).
Yes. LFNC is the preferred flexible raceway under NEC Article 680 because it contains no metal parts that can corrode from chlorine vapor or saltwater mist.
Dedicated LFNC Wire Sizing Guides
Explore individual wire gauge fill capacities and specific trade size breakdown tables:
Small Branch Circuit Gauges:
- View capacity limits for 14 AWG in LFNC conduit for 15A pool lighting whips.
- View capacity limits for 12 AWG in LFNC conduit for 20A outdoor pool pump feeds.
- View capacity limits for 10 AWG in LFNC conduit for 30A AC condenser whips.
Medium Feeder & Subpanel Gauges:
- View capacity limits for 8 AWG in LFNC conduit for 40A pool heater connections.
- View capacity limits for 6 AWG in LFNC conduit for 50A hot tub and EV charger whips.
- View capacity limits for 4 AWG in LFNC conduit for 70A and 80A subpanel flex drops.
- View capacity limits for 2 AWG in LFNC conduit for 100A and 115A equipment connections.
- View capacity limits for 1 AWG in LFNC conduit for 125A commercial feeds.
Heavy Service Entrance & Commercial Cables:
- View capacity limits for 1/0 AWG in LFNC conduit for 150A outdoor transformer taps.
- View capacity limits for 2/0 AWG in LFNC conduit for 175A distribution feeds.
- View capacity limits for 3/0 AWG in LFNC conduit for 200A generator transfer switch flex.
- View capacity limits for 4/0 AWG in LFNC conduit for 225A services.
- View capacity limits for 250 MCM in LFNC conduit for heavy commercial mains.
- View capacity limits for 350 MCM in LFNC conduit for industrial pump flex connections.
- View capacity limits for 500 MCM in LFNC conduit for heavy transformer secondary feeds.