electricallightingwiring
I purchased a home built in 1958 and a few rooms have these square recessed light boxes. I would like to hang a larger diameter modern flush-mount fixture over them, but I'm not sure what the way to do that is. Should I remove the box completely and then mount a ceiling electrical box like this in its place? I'm worried there will be a large hole in the ceiling to have to fill. Thanks!
Electrical code requires that all junctions be accessible in a box, so you definitely need one here. You have two choices (that I know of at least):
The exterior boxes come in a range of depths and colors so you should be able to find one you like.
If you can get enough access to install a BX connector on that armored cable, and if you can establish that the armor is actually a good protective ground (some armored cable only "floats" electrically), then you may be able to use a "remod box" to connect to the BX and claim your ground from the box. If none of those is true, then you really should do whatever it takes - cut access holes to be covered by the tracklight and install 2x4 remod boxes, whatever - to at the very least finish up that run with NM-B (Romex-type) cable. Given that this is for an overhead tracklight and you may not have any true grounds anywhere on that whole floor, and this house was probably wired long before grounding light fixtures became standard, you're probably legally covered.
I'm not as worried about spark containment as I could be, since the tracklight has its own termination box. Chafing of the wire insulation, though, is a bit worrisome; that's the largest reason for NM-B becoming standard. At the very very least, it'd be good to strip (without splitting) the outer sheath from a length of new NM-B and pull your two individual wires through it.
Best Answer
Inside that small access hatch in your picture you will likely find the original wire connections in a small box. Make sure that power is turned OFF either at the switch (tape the switch in the off position and put a note there so nobody turns it on while you are working) or at the circuit breaker/fuse panel. Open the access hatch and disconnect the power to the original bulb holder.
Some surface mount fixtures can be mounted directly over an open electrical box. If this is the case simply leave the access hatch cover off and wire up your new fixture. If not, and your fixture has an integral box for the electrical connection, leave the access cover off and pull the wires out of the original box and make the new connection in the integral box on your new fixture (hopefully the wires are long enough). If you must extend the wires you will have to figure out how to make pigtail connections in the original box and replace the cover (I would use a punch to create a "knock-out" hole in the access cover and feed the pigtails through a strain relief).