IMPORTANT
Quick Summary: Under the National Electrical Code (NEC Article 350 and Annex C Table C.7), Liquidtight Flexible Metal Conduit (LFMC), widely known as “Sealtite”, combines an interlocked spiral metal core with an extruded sunlight-resistant, liquidtight thermoplastic jacket. When pulling three or more conductors of the same size (THHN/THWN-2 at 40% fill), standard capacities are:
- 3/8″ LFMC (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″ LFMC: 12 wires of 14 AWG | 9 wires of 12 AWG | 5 wires of 10 AWG | 2 wires of 6 AWG
- 3/4″ LFMC: 22 wires of 14 AWG | 16 wires of 12 AWG | 10 wires of 10 AWG | 4 wires of 6 AWG
- 1″ LFMC: 35 wires of 14 AWG | 25 wires of 12 AWG | 16 wires of 10 AWG | 6 wires of 6 AWG
- 1-1/4″ LFMC: 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 LFMC conduit interior area.
- Approved for Wet & Oily Locations (NEC 350.10): LFMC is listed for direct burial (where marked), concrete encasement, outdoor sunlight exposure, machine tool oil exposure, and outdoor HVAC equipment whips.
- Equipment Grounding Rules (NEC 350.60): LFMC is permitted as an equipment grounding conductor in trade sizes up to 1-1/4″ only if the length does not exceed 6 feet and the overcurrent protection is 20A or less (for 3/8″ to 1/2″) or 60A or less (for 3/4″ to 1-1/4″). A separate green ground wire is standard trade practice.
- Wet-Rated Conductors Mandatory: Because the jacket seals against outdoor weather, moisture from condensation can accumulate inside the conduit. You must install THWN-2 or XHHW-2 wet-rated wire.
LFMC Sealtite Fill Standards At-A-Glance
NEC Article 350 Liquidtight Flexible Metal Conduit
Master LFMC Conduit Fill Chart (NEC Annex C Table C.7)
The table below provides the maximum allowable number of conductors for compact copper THHN/THWN-2 conductors inside Liquidtight Flexible Metal Conduit (LFMC) from 3/8 inch to 4 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″ LFMC (0.077 sq. in.) | 1/2″ LFMC (0.125 sq. in.) | 3/4″ LFMC (0.213 sq. in.) | 1″ LFMC (0.340 sq. in.) | 1-1/4″ LFMC (0.598 sq. in.) | 1-1/2″ LFMC (0.779 sq. in.) | 2″ LFMC (1.282 sq. in.) | 2-1/2″ LFMC (1.932 sq. in.) | 3″ LFMC (2.961 sq. in.) | 3-1/2″ LFMC (3.848 sq. in.) | 4″ LFMC (5.027 sq. in.) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14 AWG THHN | 0.0097 | 8 | 12 | 22 | 35 | 61 | 80 | 132 | 199 | 305 | 396 | 518 |
| 12 AWG THHN | 0.0133 | 5 | 9 | 16 | 25 | 45 | 58 | 96 | 145 | 222 | 289 | 377 |
| 10 AWG THHN | 0.0211 | 3 | 5 | 10 | 16 | 28 | 37 | 60 | 91 | 140 | 182 | 238 |
| 8 AWG THHN | 0.0366 | 1 | 3 | 5 | 9 | 16 | 21 | 35 | 52 | 80 | 105 | 137 |
| 6 AWG THHN | 0.0507 | 0 | 2 | 4 | 6 | 11 | 15 | 25 | 38 | 58 | 75 | 99 |
| 4 AWG THHN | 0.0824 | 0 | 1 | 2 | 4 | 7 | 9 | 15 | 23 | 35 | 46 | 60 |
| 3 AWG THHN | 0.0973 | 0 | 1 | 2 | 3 | 6 | 8 | 13 | 19 | 30 | 39 | 51 |
| 2 AWG THHN | 0.1159 | 0 | 1 | 1 | 2 | 5 | 6 | 11 | 16 | 25 | 33 | 43 |
| 1 AWG THHN | 0.1339 | 0 | 0 | 1 | 2 | 4 | 5 | 9 | 14 | 22 | 28 | 37 |
| 1/0 AWG THHN | 0.1562 | 0 | 0 | 1 | 2 | 3 | 4 | 8 | 12 | 18 | 24 | 32 |
| 2/0 AWG THHN | 0.1863 | 0 | 0 | 0 | 1 | 3 | 4 | 6 | 10 | 15 | 20 | 26 |
| 3/0 AWG THHN | 0.2223 | 0 | 0 | 0 | 1 | 2 | 3 | 5 | 8 | 13 | 17 | 22 |
| 4/0 AWG THHN | 0.2679 | 0 | 0 | 0 | 0 | 2 | 2 | 4 | 7 | 11 | 14 | 18 |
| 250 kcmil (MCM) | 0.3970 | 0 | 0 | 0 | 0 | 1 | 1 | 3 | 4 | 7 | 9 | 12 |
| 300 kcmil (MCM) | 0.4608 | 0 | 0 | 0 | 0 | 0 | 1 | 2 | 4 | 6 | 8 | 10 |
| 350 kcmil (MCM) | 0.5242 | 0 | 0 | 0 | 0 | 0 | 1 | 2 | 3 | 5 | 7 | 9 |
| 400 kcmil (MCM) | 0.5863 | 0 | 0 | 0 | 0 | 0 | 1 | 2 | 3 | 5 | 6 | 8 |
| 500 kcmil (MCM) | 0.7073 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 2 | 4 | 5 | 7 |
[!PRO TIP] Custom Outdoor Whip Calculations: Sizing custom EV charger whips, hot tub disconnects, or rooftop HVAC feeds? Calculate exact multi-conductor totals instantly with our Interactive Conduit Fill Calculator.
LFMC Dimensions and Internal Area Reference (NEC Table 4)
Liquidtight Flexible Metal Conduit is manufactured with an interlocked galvanized steel core protected by a smooth, oil-resistant thermoplastic jacket. The table below outlines internal dimensions and legal fill limits across all trade sizes.
| LFMC 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″ | 2.020 in. | 3.205 sq. in. | 1.698 sq. in. | 0.993 sq. in. | 1.282 sq. in. | 1.923 sq. in. |
| 2-1/2″ | 2.480 in. | 4.831 sq. in. | 2.560 sq. in. | 1.497 sq. in. | 1.932 sq. in. | 2.898 sq. in. |
| 3″ | 3.070 in. | 7.402 sq. in. | 3.923 sq. in. | 2.295 sq. in. | 2.961 sq. in. | 4.441 sq. in. |
| 3-1/2″ | 3.500 in. | 9.621 sq. in. | 5.099 sq. in. | 2.983 sq. in. | 3.848 sq. in. | 5.773 sq. in. |
| 4″ | 4.000 in. | 12.566 sq. in. | 6.660 sq. in. | 3.896 sq. in. | 5.027 sq. in. | 7.540 sq. in. |
Although trade sizes up to 1-1/4″ have an internal grounding strip for runs under 6 feet, master electricians always pull a dedicated insulated green copper equipment grounding conductor inside LFMC for the following reasons:
- Motor vibration causes mechanical fittings to loosen over time, compromising metal-to-metal bonding.
- Mandatory for circuits over 60 amps or runs exceeding 6 feet in length.
- Ensures 100% compliance with local electrical municipal pool, spa, and HVAC codes.
Important NEC Installation Rules for LFMC Conduit
When designing and installing Liquidtight Flexible Metal Conduit systems, keep these code requirements in mind:
- Permitted Applications (NEC 350.10): LFMC is permitted in exposed or concealed locations, for direct burial where listed and marked, in wet locations, and where flexibility is required for equipment subject to vibration (such as air compressors, chillers, and pumps).
- Approved Liquidtight Fittings (NEC 350.42): Only listed liquidtight fittings with sealing rings and ferrule compression nuts are permitted to maintain the waterproof integrity of the raceway.
- Secure Support Spacing (NEC 350.30): LFMC must be securely fastened within 12 inches of each box, cabinet, or fitting, and supported at intervals not exceeding 4.5 feet. Exceptions apply for fixture whips and motor feeds up to 6 feet in length.
- Bend Radius Limits (NEC 350.26): Total bends between pull points cannot exceed 360 degrees. Review our 360-degree conduit bend limit guide to avoid damaging the outer PVC jacket.
Frequently Asked Questions (FAQs)
FMC (Greenfield) is unjacketed flexible steel suitable only for dry indoor locations. LFMC (Sealtite) has a sunlight-resistant, waterproof thermoplastic outer jacket, making it suitable for outdoor, wet, and oily industrial locations.
Under NEC Annex C Table C.7, you can install up to 5 conductors of 10 AWG THHN/THWN-2 in 1/2-inch LFMC conduit under the 40% fill limit.
A standard 50-amp hot tub using three 6 AWG copper conductors plus one 10 AWG ground wire (0.1732 sq. in. total) requires a minimum 3/4-inch LFMC conduit (0.213 sq. in. capacity).
Yes, but only if the conduit is explicitly stamped and marked “Direct Burial” by the manufacturer in accordance with NEC 350.10(3).
Dedicated LFMC 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 LFMC conduit for 15A outdoor lighting whips.
- View capacity limits for 12 AWG in LFMC conduit for 20A rooftop receptacle feeds.
- View capacity limits for 10 AWG in LFMC conduit for 30A AC condenser whips.
Medium Feeder & Subpanel Gauges:
- View capacity limits for 8 AWG in LFMC conduit for 40A compressor feeds.
- View capacity limits for 6 AWG in LFMC conduit for 50A EV chargers and hot tub whips.
- View capacity limits for 4 AWG in LFMC conduit for 70A and 80A subpanel flex drops.
- View capacity limits for 2 AWG in LFMC conduit for 100A and 115A equipment connections.
- View capacity limits for 1 AWG in LFMC conduit for 125A commercial feeds.
Heavy Service Entrance & Commercial Cables:
- View capacity limits for 1/0 AWG in LFMC conduit for 150A outdoor transformer taps.
- View capacity limits for 2/0 AWG in LFMC conduit for 175A distribution feeds.
- View capacity limits for 3/0 AWG in LFMC conduit for 200A generator transfer switch flex.
- View capacity limits for 4/0 AWG in LFMC conduit for 225A services.
- View capacity limits for 250 MCM in LFMC conduit for heavy commercial mains.
- View capacity limits for 350 MCM in LFMC conduit for industrial motor flex connections.
- View capacity limits for 500 MCM in LFMC conduit for heavy transformer secondary feeds.