What fitting connects flex conduit to rigid conduit?

A listed combination coupling, threaded on the rigid side and flex on the other, or a flex connector threaded into a rigid coupling. NEC 110.3(B), 348.6 and 344.42 require listed fittings for the transition.

Does flexible metal conduit count as an equipment ground?

Only under NEC 348.60: fittings listed for grounding, circuit protected at 20 amperes or less, total ground return length of 6 feet or less, and the flex is not installed for flexibility after installation. Otherwise pull a separate EGC per Table 250.122.

Can I use standard FMC outdoors after rigid conduit?

No. Standard flexible metal conduit is a dry location wiring method. Use liquidtight flexible metal conduit or LFNC with wet location listed fittings for outdoor and rooftop transitions.

Can you connect flexible conduit to rigid conduit?

Yes. Going from rigid metal conduit or IMC into flexible metal conduit is an everyday transition, usually at a motor, a rooftop unit, or a piece of vibrating equipment. The part that trips people up is not whether it is allowed, it is which fitting you are permitted to use and what happens to your equipment grounding path.

Use a fitting listed for the job

Section 110.3(B) of the 2023 NEC requires listed equipment to be installed and used per its listing. Article 348.6 says fittings for FMC shall be listed, and 344.42 says the same for RMC couplings and connectors. A combination coupling, threaded on one end and flex on the other, is the listed product built exactly for this transition. Screwing a flex connector into a rigid coupling is the other clean method, because the flex connector is threaded on the box end and that thread mates with the rigid coupling.

What you cannot do is force one raceway inside the other, use a setscrew EMT coupling to grab rigid conduit, or slide the flex over the rigid and band it. Those are not listed connections and an inspector will call them out under 110.3(B) and 300.15.

Watch the grounding path

This is where most rejections happen. Section 348.60 permits flexible metal conduit to serve as the equipment grounding conductor only when all of the following are true: the conduit is terminated in fittings listed for grounding, the circuit conductors are protected at 20 amperes or less, the combined length of the flex in the ground return path is 6 feet or less, and the flex is not installed for flexibility after installation. If the run is longer than 6 feet, the breaker is larger than 20 amperes, or the flex exists specifically to absorb motion, you must pull a separate wire type equipment grounding conductor sized from Table 250.122.

Liquidtight flexible metal conduit gets similar but not identical treatment in 350.60, which allows it as a ground path up to 6 feet with 60 ampere and smaller protection in trade sizes 3/8 through 1/2, and 20 ampere and smaller in the larger conditions listed there. Read the section rather than assuming FMC and LFMC behave the same.

Length, support, and location

Section 348.20(A) sets the minimum length for FMC in trade size 3/8, and 348.30(A) requires support within 12 inches of every box, cabinet, or fitting, then at intervals not exceeding 4 1/2 feet. There is an exception for lengths up to 3 feet at terminations where flexibility is needed, and 6 feet for luminaire whips per 348.30(A) Exception No. 4.

Standard FMC is a dry location product. If the transition is outdoors, on a roof, or anywhere the raceway can get wet, use LFMC or LFNC with fittings listed for wet locations, and remember that 300.5 and 358.42 style raintight requirements exist for a reason.

Field takeaway

Buy the combination coupling, or thread a flex connector into a rigid coupling. Pull a green wire through the flex any time the run exceeds 6 feet, the overcurrent device exceeds 20 amperes, or the flex is there to take vibration. Support the flex within 12 inches of the fitting unless one of the flexibility exceptions applies.