1

I want to run some FMC from the bottom of my main panel and out the wall and connect into EMT.

Is there a proper connector to join the FMC to an LB? I'm assuming you can't just use the set screw in an EMT LB.

My original plan is to drill a knockout in the back of a metal junction box and use an FMC->Threaded connector and terminate it that way, then connect the EMC to a side knockout and fish the wire through. I'm wondering if there is an easier way to just connect the FMC to an LB.

Do the threads on a FMC to JB connector fit in the threads of a rigid LB?

The bend in the FMC + connector needs to be able to fit in a 2x6 wall.

*** Edit ***

Current plan: From the main panel (which is mounted in the wall), I want to run a short piece (~3ft) of 3/4" FMC down the wall behind drywall and bend it to a 90 degree elbow to meet up with an LB on the surface of the drywall. The FMC will connect with the short side of the LB with the cover facing out. The connection between the FMC and LB will likely be behind/within the drywall. On the long end of the LB, I will have a run of 3/4" EMT (~40ft) that will terminate at a 2 gang metal box that will house a 14-50 outlet (box sized properly for the outlet). In this conduit run, I will have 3 #6 wires (black, black, white) and a #10 ground wire (green), all THHN. I plan to terminate the green wire in the outlet box as well as connect it to the correct terminal on the outlet using a 2 hole mechanical lug. Using #6 as I may convert this from a 50amp circuit to 60amps in the future (for an EV charger).

I'm using FMC as I don't believe I can make a 3/4" EMT sweep elbow work in the 2x6 wall (not enough room). I understand that FMC can be used to ground the run in certain situations, but I am running the ground anyway. It sounds like it may be needed if I use a connector from the FMC to LB that isn't necessarily meant for that purpose. I have taken into consideration pull points along the way due to the number of degrees of bends in the conduit.

The conduit body / LB I'm planning on using is a Morris 14247. Not sure if it is volume marked or not. From what I understand, for #6 wire and smaller, you can use the same size conduit body as the conduit you are using for your run (assuming wire fill is appropriate).

If the FMC / LB connection is questionable, I will just replace the LB with an 8x8 junction box (yup probably too big) and connect the FMC to the back of the junction box and run the wire out through the side into EMT.

2 Answers 2

2

Yes there are proper connectors for FMC to EMT. See picture below. You'd need to add a small piece of EMT and an EMT to JB connector. enter image description here

The threads of a FMC to JB will fit into a rigid LB but are designed for lock nuts so not necessarily to code. Grounding could be compromised. See @ThreePhaseEel comment.

6
  • Is using a FMC to JB connector to go into the threads of a LB approved by code? Aug 20, 2021 at 22:25
  • @B.Anderson -- not necessarily -- threads on fittings are designed for locknuts not hubs, thus UL doesn't test JB connectors threaded into hubs, and they may not provide good grounding continuity as a result Aug 21, 2021 at 2:22
  • @ThreePhaseEel Thanks for the clarification. I have used them into threaded LB's but always ran a ground wire.
    – JACK
    Aug 21, 2021 at 11:55
  • I was planning on running a ground wire and connecting to the box and outlet at the end of the run. Would this work? Aug 21, 2021 at 12:06
  • @B.Anderson the conduit body still needs to be grounded properly, which raises questions of its own: is this conduit body volume marked, and how are you providing access to it down the road? (Conduit bodies are like boxes in that you can't legally bury them in the wall) Aug 21, 2021 at 12:58
1

Rigid parts give us the flexibility we need

While flexible conduit seems like an attractive option for making the "around the horn" bend behind the drywall, it doesn't work so well due to the issue that flexible conduit fittings are designed to work with junction boxes, not conduit bodies with their built-in conduit hubs, or any other sort of hub fitting for that matter. (The issue has to do with grounding continuity, thread type mismatches, and UL testing; this piece by UL's Mark Ode discusses the problem in more detail.)

Instead, with your choice of a rigid/EMT combination LB, I'd use a rigid conduit nipple threaded into the short end of the body to penetrate the drywall, then thread the female end of a rigid conduit short elbow fitting (Appleton LMFL90-75 or equivalent) onto the other end of the nipple. This then lets us use a standard rigid coupling to attach an EMT-to-threaded-hub transition fitting (Bridgeport 291-RTNPT) to the short elbow, thus getting us around the horn without violating any UL listings or the NEC, as factory-produced short radius fittings are permitted in conduit runs. (See NEC 344.24 for the operative language.)

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.