The old switch probably was a 4-way. That is a variation of a double-pole, double throw. One solution is to use a surface extension, such as Wiremold. Available in various depths. Not necessarily the most attractive solution. If you decide to replace the existing box, look at the possibility of cutting into the wall behind the box. Will that side be easier to patch?

Here is a link that might be useful: Wiremold

Wire mold just looks like hell.

I have to use it in SCIF exterior walls since no wiring of any kind is allowed inside the walls, and it still looks bad.

Hey brick, nice to see you over here and thanks for the great advice. I had gotten a plaster ring so it was good to know I was on the right track. It seemed to me to make sense to enlarge the box, but I always wonder if a pro would hit me over the head with linesman's pliers and call me a dufus every time I try to "innovate" like that! yes, I know when in doubt call a pro, but for a switch replacement I really wanted to go it on my own.

I'm still working on those NEC tables; I found one online with a free one-day trial so I'm going to wait until I open up another problematic box and look everything up at once while I've got the free trial.

Bus driver, thanks for the tip about the wire mold. Since I got the bigger box in I'll stick with that, but it's nice to know it exists. Another one for the bag of tricks.

I did not appreciate running into this problem at all; the power to the circuit had to be left off for hours while I ran around getting more boxes and tools. If I were a pro working on a fixed-price job, I'd be cheesed at losing money because something took so much longer than expected. On the other hand a pro would be prepared for the contingency and it would have gone from a 15 minute job to a 30 minute job. For me, it went from minutes to hours. But I'm sure it's not the last time I run into this problem, so I'm glad I've got it figured out.

Thanks all, great forum. Really liked the thread about the guy running power out to his shed--now THAT is definitely a job I would not tackle on my own. But I am going to look at how the power is run out to my garage. I bet it was a hack job and will need to be replaced. We are slowly replacing a lot of the wiring in this old house. (Don't even ask me about how the attic fan was wired, scary!) But at least we had no K&T. And we've got arc faults on all the bedroom circuits, so I sleep a little better at night.

This is one area where I would consider using the plastic push in connectors since the wires can rotate in them. It 'seems' like you would be given some added flexibility and have an easier time getting everything to stay in place better. If your not up to par on the wire nutting this method might be better in the long run.

I know I know.. wire nuts are unbeatable if the wire is twisted good and trimmed to the proper length and the right size nut is used. If the wires are just shoved in for three twists and then poked prodded and jammed into the box its a recipe for a mess.

There are older code copies that can often be viewed for free (though you may need to register) an the National Fire Protection Association.

The box fill table has not changed in many years.