EMT Compression vs Set-Screw Fittings: NEC 358, Raintight Ratings and Where Each One Passes Inspection
Sep 08, 2026
EMT fittings look interchangeable on the shelf, and on a dry interior run they are. The moment the conduit leaves the building, goes into a slab or picks up a grounding duty, the choice matters, and inspectors know the difference on sight.
The two families
Set-screw fittings clamp the tubing with one or two screws through a die-cast zinc or steel body. Fast, cheap, listed for dry and damp indoor locations under UL 514B, and acceptable for concrete-tight when so marked. Compression fittings squeeze a gland ring onto the tubing with a nut; when marked raintight they are listed for wet locations, and when marked concrete-tight they can be poured into a slab. Both provide the equipment grounding path required by NEC 358.60 and 250.118 when properly made up.
NEC 358 in one paragraph
358.10 permits EMT in wet locations if the fittings are listed for the purpose, which means raintight compression. 358.42 requires threadless couplings and connectors to be made up tight, and if buried in masonry or concrete, to be concrete-tight. 358.30 sets support at 10 ft intervals and within 3 ft of every box, using one-hole straps, two-hole straps or conduit hangers. Insulated-throat connectors are required by 300.4(G) where 4 AWG or larger conductors enter an enclosure.
Location by location
| Location | Connector | Coupling |
|---|---|---|
| Dry interior, exposed | Set-screw, die-cast | Set-screw |
| Dry interior, 4 AWG and larger | Set-screw insulated throat | Set-screw |
| Above suspended ceiling, plenum | Set-screw steel | Set-screw steel |
| Slab or masonry | Compression, concrete-tight | Compression, concrete-tight |
| Exterior, exposed to weather | Compression, raintight, insulated | Compression, raintight |
| Car wash, food plant, washdown | Stainless or PVC-coated rigid instead | |
| EMT to flex transition | Combination coupling |
Die-cast zinc or steel
Zinc die-cast set-screw fittings are the volume product and are fine indoors. Steel fittings are required by some specifications and by many utilities for the grounding path on larger sizes, and hold up better where the conduit gets bumped. Both are UL 514B; the spec sheet tells you which. CT EMT connectors are stocked in both, 1/2 through 2 in, plus 3 in rigid compression.
Rigid and IMC, briefly
Rigid conduit bodies in LB, LL, LR, T and C shapes come threaded for rigid and IMC, and in set-screw for EMT. Threaded bodies are the wet-location choice; copper-free aluminum bodies are lighter and do not rust, and are what most of the conduit body line is made from. Threadless compression couplings join rigid without threading in the field; they are concrete-tight but not raintight unless so marked.
Locknuts and bushings
Every EMT connector gets a locknut inside the box; anything 1-1/4 in and larger, or carrying 4 AWG and up, gets an insulated bushing. Where the raceway is the grounding path for a service or a separately derived system, 250.97 wants a grounding bushing with a lug, bonded to the enclosure with a jumper. Locknuts, insulated bushings and grounding bushings are stocked 1/2 through 2 in.
All CT conduit fittings are UL 514B listed and ship same day from Oxnard, CA. Case pricing applies at 25 pieces and up.
