But how do you guys cope with all those different versions?

Quite simply really since we have two different electrical license classifications. The first being restricted which basically limits you to residential type work under 400amps which is all single phase, 3wire.

Then in order to work on commercial/industrial type stuff you need the unrestricted license. Which covers the 120/208 and the 277/480 and even some of the older type of stuff when they used to use the delta transformers instead of the WYE type transformers that we use now. In a commercial building you basically can look around in the switchgear room and if you don't see any transformers a quick assumption would be that it's 120/208, if there are transformers in the gear room then typically that would mean there was a 277/480volt service. In a 277/480volt building typicall all fluorescent, HID lighting loads would be 277, the RTU's would be 480v 3phase and your incandescent lighting and convenience ereceptacles would be 120volt.

I have seen some electricians unpleasantly surprised when they tried tripping a 277volt circuit to cut off the power instead of flipping off the breaker. 277 will melt your kleins pretty good.

A tester definately comes in handy.