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trying to add an outlets in basement. The joists at the locations of interest are super crowded, so I was just going to run THNN in some conduit. A friend offered me free 3/4" LFC, said it should be totally okay to use it in an unfinished basement and easier than EMT.

I need to secure the run to the bottom of joists. Is it okay to use 3/4" rigid hangers? Any suggestions on what fasteners to use when drilling into bottom of joists? Do I need to do pilot holes for hangers, or is it safe to just drill in? Also, need to add some junction boxes. Similar questions about typically used fasteners, are pilot holes necessary, etc.

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  • IME your free conduit might get a bit expensive by the time you get the right connectors for a few boxes, but see what you find locally...
    – Ecnerwal
    Commented Sep 27, 2020 at 21:19

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LFNC is not pretty but it's easy to install. You have to strap it every three feet and within one foot of the boxes. You can't exceed 360 degrees of accumulated bend between boxes. Since it's impossible to get the stuff really straight, and it's sticky inside, you're better off limiting it to 270 degrees of bend between boxes.

The straps made for rigid metallic conduit or PVC conduit should fit well enough, and two hole straps will work well enough where running perpendicular to the joists. Parallel to the joists, straps probably won't fit along the bottom of the joist, but you can just strap the conduit to the face of the joist instead of the bottom edge.

If you use reasonably small screws, like #10 or smaller, splitting the joist is unlikely, but it never hurts to drill pilot holes.

Use gray surface mount type plastic junction boxes and drill right through the back of the boxes to secure them to the joist. You could use two of the four mounting tabs on the box but they'll tend to snap right off.

pvc junction box

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  • One problem -- FS/FD style plastic boxes use hubs designed for rigid conduit, and are not listed for use with LFNC, either directly or via fittings. ENT-type new work boxes are a much better bet, as they'll accept all sorts of conduit connectors.
    – ThreePhaseEel
    Commented Sep 27, 2020 at 23:14
  • Thank you for the response - had two follow up questions: 1) Can I not use metal gangboxes with the proper LNFC fittings? My understanding was that as long as I bond the box to the ground wire I'm running through the conduit, I could use those instead of plastic boxes (was offered free metal boxes and fittings as well). 2) Are there any restrictions regarding how the LNFC is shaped between the 36" of straps? My goal was to do a 90 deg to bend down from ceiling joists to travel down a wall a bit, strap to cinderblocks.
    – Mitchell Bieniek
    Commented Sep 27, 2020 at 23:37
  • Yes you can use metal boxes as long as you bond the boxes, and yes you can bend the flexible conduit.
    – batsplatsterson
    Commented Sep 28, 2020 at 0:21
  • Okay. And so I can run a single ground wire (was offered 12AWG solid) from the main box to the j-boxes, bond at the J-boxes, and then tie into the j-box ground for the two circuits I plan on adding? Or do I need to run individual ground wires for each circuit, + a ground for the j-boxes?
    – Mitchell Bieniek
    Commented Sep 28, 2020 at 18:22
  • Sorry for double comment - My interpretation of 250.122(C) suggests that I should only have to use 1 ground wire sized for largest circuit (so 12 AWG for three 20A circuits), bond it to each junction box, and pigtail the outlet connection to the junction box to ensure that removing any outlet would not interfere with the rest of the grounds. Is that a correct interpretation?
    – Mitchell Bieniek
    Commented Sep 28, 2020 at 18:36

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