Where to Use Rigid Compression Fittings: Application Guide for RMC and IMC
Sep 25, 2026
Threadless compression fittings for rigid metal conduit (RMC) and IMC solve a specific set of jobsite problems. This guide walks through the situations where they earn their place, the ones where a threaded fitting is still the right call, and how to spec them by location. For part numbers, sizing and cross references, see the Rigid Compression Fittings Buyer's Guide.
The short version
Use a rigid compression coupling or connector any time you have unthreaded rigid or IMC and no practical way to thread it: field cuts, tie-ins to existing runs, tight spaces, repairs, and any job where the threader stayed on the truck. They are listed under UL 514B and permitted by NEC 344.42(B) and 342.42(B) when listed for the purpose.
Where they are used
1. Commercial and industrial tie-ins
The most common application. An existing rigid run feeds a panel, gutter or trough, and a new circuit has to enter the same enclosure or splice into the run. The pipe is fixed at both ends, so it cannot be rotated into a threaded coupling. A compression coupling (RTC series) joins the new stick to the cut end; a compression connector (RT series) brings it into the enclosure.
2. Field cut lengths
Rigid comes in 10 ft sticks with a coupling on one end. Every run ends in a cut length. With a threader on site you thread the cut end; without one, a compression coupling or connector finishes the run. On service work and small crews this is the difference between finishing today and coming back tomorrow.
3. Repairs and damaged sections
Vehicle strikes, corrosion at grade, and demolition damage all mean cutting out a section of an existing rigid run. Two compression couplings and a new piece of conduit restore the raceway without disturbing the runs on either side.
4. Tight spaces and short nipples
Between a disconnect and a motor starter, through a wall, or inside a mechanical room where you cannot swing a stick, a compression connector on each end of a short cut nipple is faster and cleaner than trying to thread a piece that is too short to hold in a vise.
5. Concrete encased and slab work
Our RT series connectors and the RACO 1800 series crosses are listed concrete tight. On slab-on-grade and tilt-up work where rigid stubs up into panels and equipment pads, a compression connector at the enclosure keeps the entry concrete tight without a threaded hub.
6. Retrofit and tenant improvement
Existing rigid in the ceiling, new tenant below. Extending or re-routing existing runs is almost always a compression fitting job because the existing pipe is supported, hidden and unthreadable in place.
7. Solar, EV and equipment pads
Rigid risers from underground to inverters, EVSE pedestals and transformer pads frequently need a field cut at grade or at the equipment. A compression coupling at the transition and a compression connector at the enclosure are the standard finish.
Where a threaded fitting is still the right choice
- Hazardous (classified) locations. Class I and Class II areas under NEC 500 series articles require threaded conduit systems. Threadless fittings are not permitted there.
- Wet locations with a plain concrete tight fitting. A concrete tight listing is not a wet location listing. Outdoors or where the fitting sees water, use a fitting listed raintight (for example Bridgeport's 3000-RT and 3100-RT series) or a threaded fitting with a listed hub.
- Direct burial and corrosive environments. Zinc plated steel is for indoor and protected outdoor use. Specify a fitting listed for the environment.
- Jobs specified threaded. If the spec or the AHJ calls for threaded joints, follow the spec.
Specifying by location
| Location | Fitting | Listing to confirm |
|---|---|---|
| Indoor dry, exposed or above ceiling | RTC coupling, RT connector | UL 514B |
| Concrete encased, slab stub-ups | RT connector at enclosure | UL 514B, concrete tight |
| Outdoor, wet location | Raintight listed fitting (Bridgeport 3x00-RT class) or threaded | UL 514B, raintight |
| Hazardous (classified) | Threaded only | NEC 500 series, no threadless |
| Direct burial, corrosive | Fitting listed for the environment | Per listing |
Grounding continuity
Where the rigid raceway is the equipment grounding conductor, the fitting is part of the ground path. Ream the conduit, seat it fully, and tighten to wrench tight so the compression ring bites clean metal. If the conduit is painted or corroded at the cut, clean it back to bright metal first.
Sizes and stock
We stock 1/2" through 2" couplings (RTC-50 to RTC-200) and connectors (RT-50 to RT-200), sized to RMC/IMC outside diameter. Same-day shipping on in-stock items. Case and pallet pricing through the trade desk at 1 (307) 206-0534. Browse the Rigid and IMC Compression Fittings collection.
