Liquid-tight conduit is a flexible raceway that seals out water and dust, sold in the US as PVC-based LFNC (like Type B) or metallic LFMC.
Water finds the seam, and the run fails. Liquid-tight conduit keeps liquids, dust, and contaminants off the conductors while bending around corners and vibrating equipment. US listings show two families: nonmetallic liquidtight flexible conduit (LFNC, including Type B, or LFNC-B) and liquidtight flexible metal conduit (LFMC). The 1-1/2 inch trade size is standard in both and pairs with matching 1-1/2 inch liquid-tight connectors. Here’s how they differ and the dimension mistake that trips up buyers.
Nonmetallic vs Metallic: Which Type Handles Your Run?
Nonmetallic Type B (LFNC-B) is a PVC core that keeps oil, water, and sunlight off conductors. It resists corrosion, weighs less, and bends by hand, but heat, sharp edges, and heavy traffic can damage it, and it provides no grounding path alone.
LFMC wraps a steel or galvanized-steel core in a liquid-tight jacket. Bend-radius and temperature data vary by family. The steel core resists impact, holds shape, and supports equipment-grounding continuity with listed fittings.
Chemical washdown, salt air, or corrosive splash zones point to nonmetallic. Vibrating machinery or forklift traffic points to the metallic type.
What Do the Ratings and Dimensions Actually Tell You?
Ratings are type- and product-specific, and trade size is not actual diameter — 1-1/2 inch conduit measures roughly 1.58 inches inside and about 1.87 to 1.88 inches outside.
A Carlon LFNC-B listing, model 15010-150, gives 1-1/2 in trade size as 1.58 in ID by 1.882 in OD, in PVC, with an 80 °C dry and 60 °C wet rating, UL File No. E79553, and a 150 ft length. Dry and wet limits differ, so ambient and moisture conditions must match the product rating.
An LFMC listing, part 6206-24-00, shows 1.58 in ID and 1.87 in OD across a 50 ft nominal length. Trade size is a nominal label, so actual IDs and ODs shift between families and manufacturers.
Look for UL file numbers, CSA certification, and on some products RoHS, Buy American, and ARRA compliance. Superflex’s 1-1/2″ Type B listing carries UL file E129973 and CSA certification, with an 8 in minimum bend radius.
Does 1-1/2 Inch Conduit Need a Matching Connector?
Yes — fittings are type-specific, and a connector listed for Type B should not be assumed to work on the metallic version, or the reverse.
ABB’s LT150P is listed for terminating Type B liquidtight non-metallic conduit or flexible non-metallic tubing to a box or enclosure, in 1-1/2 inch. Match the connector’s listing to your conduit’s type and trade size. Get it wrong and the failure is quiet — a fitting that threads on but does not seal. The 1-1/2 inch size also has real weight and stiffness, so plan a bend radius your run can accommodate (8 in minimum on the Superflex listing) before committing to a path.
| Product Example (1-1/2 in Trade) | Key Listed Specs | Notable Detail |
|---|---|---|
| Carlon 15010-150 (LFNC-B) | 1.58 in ID x 1.882 in OD, PVC | 80 °C dry / 60 °C wet, UL E79553, 150 ft |
| Superflex Type B (LFNC-B) | Part 8435, 1-1/2 in, 100 ft as 8435-100 | UL E129973, CSA, 8 in min bend radius |
| LFMC 6206-24-00 | 1.58 in ID x 1.87 in OD | 50 ft nominal length |
| ABB LT150P connector | 1-1/2 inch liquid tight connector | Listed for Type B non-metallic conduit |
If you’re comparing brands before buying, the tested picks over at the 1 1 2 inch liquid tight conduit roundup walk through specific options in this exact trade size.
Southwire’s liquid-tight reference section covers conduit types, fittings, and installation requirements in more depth. Southwire’s liquid-tight conduit reference lays out the type and sizing details manufacturers expect installers to know.
Two things decide most 1-1/2 inch jobs. Match the conduit type to the environment — LFNC-B for corrosive and wet spots, LFMC where impact and grounding continuity matter. Treat “1-1/2 inch” as a trade-size label: confirm actual ID and OD, then buy a connector listed for that exact type and size. Confirm temperature ratings against dry and wet conditions and check minimum bend radius fits your run.
FAQs
Can I use the same fittings on metallic and nonmetallic conduit?
No. Connector listings are type-specific — ABB’s LT150P, for example, is described for Type B liquidtight non-metallic conduit. A fitting listed for LFMC should not be assumed to seal on an LFNC-B run of the same nominal size.
Is 1-1/2 inch trade size the same as 1.5 inches of inside diameter?
No. Trade size is a nominal label. A 1-1/2 inch LFNC-B listing shows 1.58 in ID and 1.882 in OD, and a comparable LFMC listing shows 1.58 in ID by 1.87 in OD. Actual dimensions vary by family and manufacturer.
What does a 60 °C wet rating mean in practice?
The conduit’s temperature limit changes with moisture. The Carlon LFNC-B listing gives 80 °C dry and 60 °C wet, so a run exposed to water has a lower ceiling. Match dry and wet ratings to actual ambient and moisture conditions.
References & Sources
- Southwire. “Liquid-Tight Conduit Reference, Section 2.” Product reference covering liquid-tight conduit types, fittings, and sizing.
- ABB. “LT150P Liquid Tight Connector, 1-1/2 Inch.” Lists connector compatibility with Type B liquidtight non-metallic conduit.
- ABB. “LTXES02B-C Liquid Tight Product Listing.” Additional liquid-tight fitting reference for sizing and type compatibility.
