Got a call to bail out a local (read "young") electrician in Alexandria (VA) last Friday. He had come upon a set of what we call "Old Code 3 ways". I think half of old (~50yrs) Alexandria is wired this way. We experienced (read "old") electricians have seen it many times. I learned it from an even more experienced (read "older") electrician I did my apprenticeship under. It's been illegal for 40+ years now but there's still a lot in existance. Wondering if other parts of the country have this also.
Bring a constant hot/neutral to the first S3. Run a 3 cond to the second S3. (Then run a 2 cond to power the receps after the second S3) In the first box join the 2 hots and jump to a traveler screw. Join the 2 neutrals and jump to the second traveler. Put the red on the Common. In the second S3 also join the hot and feed thru hot and jump to a traveler. Same with the neutrals. At this point send a 2 cond to the bulb and put one wire on this common termimal and attach the other to the red (which is the other common). Polarity and color are irrelevant since we're gonna flip flop them anyway. It works by sending 1 of 4 configurations to the bulb, (hot/neut, hot/hot, neut/neut, neut/hot) 3 of which are illegal but it was used extensively back in the day. Worst part is that the house was completely finished and there was no way in h*** the homeowner was gonna let him cut any walls to fix it. Well fortunatly it wasn't my job so I drew him a diagram, filled him in on the legalities/liabilities and left.
You guys run into this system much? (I have a PDF of the diagram I drew if anybody wants it but for all the tea in China I could not figure how to attach it to this post ... email me, I'll send it if you want it)