EMT Fittings Guide: Set-Screw vs Compression vs Raintight, and What NEC 358 Requires
Sep 03, 2026
EMT (electrical metallic tubing, NEC Article 358) is the most-installed raceway in commercial work, and the fittings are where jobs pass or fail inspection. This guide covers the three connector/coupling families — set-screw, compression, and raintight compression — what the listing marks mean, and the NEC rules that decide which one you can use. Products: EMT Fittings.
1. The three families
| Set-screw | Compression | Raintight compression | |
|---|---|---|---|
| How it grips | Screw bites the tube wall | Split ring compressed by a gland nut | Compression ring plus sealing ring / gasket |
| Listing | UL 514B; dry / damp locations; concrete-tight where marked | UL 514B; concrete-tight; dry / damp | UL 514B raintight (wet locations) — look for "RT" on the fitting |
| Material | Zinc die-cast (most common) or steel | Steel (zinc plated) or die-cast | Steel, zinc plated |
| Speed | Fastest — one screw | Wrench on the nut | Wrench, plus the sealing ring must seat |
| Typical use | Indoor branch and feeder runs, above ceilings, interior walls | Where vibration or pull-out matters, concrete pours, exposed indoor | Outdoor, rooftops, wash-down, anywhere subject to rain or hose |
Insulated throat is a separate option on connectors: a thermoplastic liner that protects conductor insulation at the box entry. NEC 300.4(G) requires an insulating bushing or fitting for conductors 4 AWG and larger; an insulated-throat connector satisfies it without a separate bushing.
2. The code rules that pick the fitting
- NEC 358.42 — couplings and connectors. Must be made up tight. Set-screw fittings are permitted; where buried in masonry or concrete they must be concrete-tight; where installed in wet locations they must be listed for wet locations (the raintight mark). Threadless fittings are the norm for EMT — EMT is never threaded.
- NEC 358.10 / 358.12 — where EMT can go. Permitted exposed, concealed, in concrete, in direct contact with earth (with corrosion protection), and in wet locations with raintight fittings. Not permitted where subject to severe physical damage, in cinder fill without protection, or in hazardous locations except as specified.
- NEC 300.4(G) — insulated bushing or fitting for 4 AWG and larger.
- NEC 250.97 / 250.92 — grounding bushings and bonding jumpers on concentric knockouts over 250 V and at service equipment. A locknut alone is not a bonding means there.
- NEC 358.30 — support. Fastened within 3 ft of every box, cabinet, or fitting and at intervals not over 10 ft. See EMT Support Spacing.
3. Reading the marks
"UL 514B" — fittings for conduit, tubing, and cable. "Concrete-tight" — keeps wet concrete out during a pour (nearly all set-screw and compression fittings). "Raintight" — keeps rain out under UL's spray test; only fittings with a sealing ring carry it. "Wet locations" on the carton means the same as raintight. Die-cast zinc vs steel is a durability and torque choice, not a listing difference: steel compression fittings take more wrench without stripping and are the better pick on 1-1/4" and larger.
4. Sizing and installation
- Match the trade size to the tube: 1/2" through 4" EMT; the fitting throat is sized to the EMT OD (0.706" for 1/2", 0.922" for 3/4", 1.163" for 1").
- Cut square, ream the burr. A burr under a compression ring causes the ring to split; under a set-screw it prevents full seating.
- Set-screw: bottom the tube in the fitting, tighten the screw until it bites — the screw head should not shear. Two-screw fittings on 1-1/4" and up: tighten both.
- Compression: hand-tight plus a half turn with a wrench; on raintight, until the sealing ring is visibly compressed against the tube.
- Connector into the box: locknut inside, wrench-tight, then the bushing or grounding bushing. Locknut teeth must bite bare metal, not paint.
5. Cross-reference notes
Our steel compression connectors and couplings cross to RACO 29xx (2902–2908 connectors, 2922–2928 couplings); set-screw die-cast to RACO 28xx / 20xx and Bridgeport 240-DC series; raintight to RACO 29xxRT. Locknuts cross to RACO 1002–1008 and Bridgeport 101-S–106-S; one-hole EMT straps to RACO 2082–2088. Every product page lists its crosses. Related: Rigid vs EMT couplings · Grounding bushings and locknuts — NEC 250.97 / 250.92.
