Electrical Conduit – How to Remove Metal Ring on Flex Conduit

It sounds like you're sheetrocking over the existing wiring. If that's correct, I think this would work. The challenge is you want to make the transition from conduit to plain NM in a box, and you want the plain NM concealed inside a wall, not out in the open where it's exposed to damage.

• remove the box from the end of the conduit
• install two boxes in the face of the new wall, maybe one at switch or sconce height, one at receptacle height. (These boxes will be accessible through the new sheetrock.)
• Cut the existing NM mid way between the new boxes
• extend the conduit to the upper box (with the NM in it)
• splice in a new piece of NM from the upper box to the lower box

The answer is fully dependent on:

1. Whether the location is subject to physical damage.
2. Conduit fill (for the 3/4" size) and planned amperage of the circuit.

For item 1, flex conduit cannot be used where subject to physical damage.

From NFPA-70:2014 (2014 NEC):

ARTICLE 348 Flexible Metal Conduit: Type FMC

348.12 Uses Not Permitted. FMC shall not be used in the following:

(7) Where subject to physical damage

"Subject to physical damage" is subject to the inspector's opinion since the NEC does not explicitly define these terms, so I would recommend consulting with them.

Generally, wiring at a height less than 8 ft is an unwritten convention that is typically considered subject to physical damage p(rovided there are no other surround protections/enclosures/guard strips and then you're back to the inspector's interpretation).

For item 2, once you have selected the wire size appropriate to supply the required current on the circuit, you will need to calculate conduit fill to determine the allowable size of the conduit/raceway (refer to Informative Annex C of the NEC).