Installing flexible metallic conduit into old work boxes
Most electrical codes permit fishing a length of flexible conduit into a finished wall, but the problem always has been how to connect the connector easily to an old work box (these switch or outlet boxes are used in remodeling, when it’s easier to clamp the box to drywall rather than nail it to a stud).
It’s easy enough to install the box. The problem is how to guide the threaded coupling at the end of the flexible conduit into the box, then hold it there securely while putting on the lock nut.
My solution to this problem is a length of #12 solid wire. As shown in the drawing, I bend one end of the wire into a J-hook, with the tip of the wire slightly open. The hook should be longer than the inside diameter of the flex connector. With the lock nut removed, I insert the hook into the connector and catch its back edge with the hook.
I guide the wire into the knockout hole in the box, and using the wire as a handle, I pull the conduit and its connector into the box. Now it’s an easy matter to slip the lock nut onto the wire, slide it over the connector, and thread it home. Jerk the wire out of the conduit and you’re done.
— Richard A. Olsen , North Hollywood, CA
Edited and Illustrated by Charles Miller
From Fine Homebuilding #176
Why would you go to this much of a hassle when you can remove a old work box and do that work on the outside of the wall?