Frequency, 50 or 60Hz?
Some people have claimed that the frequency is very important for X10 to work properly. I even saw "Mr Module" in the Electronic House Magazine claiming this. This is false except for the case of "three phase transmit" mentioned earlier. Well if someone makes an X10 clock which is synchronized onto the main frequency, the clock might not work properly but this is not a problem with X10, it is a problem with the clock. Anyway, I have not seen such a device. Even a CP290 has a crystal controlled clock with battery backup and the X10 communication is synchronized with the zero crossover of the supply, whatever the frequency is.
Note that this problem with "three phase transmit" only relates to modules that transmit data. Receivers like lamp and appliance modules will work fine on both 50 and 60Hz since they only listen for data at the zerocrossing.
I have reverse engineered several 220V modules and 110V modules and there are, at least not on receivers, any differences between 50 and 60Hz. Besides, I live in a place were we have 220V 50Hz and I have a backup generator 220V 60Hz! I never changed the frequency of the generator because that would mean lowering the RPM and loosing about 15-20% of the rated power output.
Anyway, when my Timecommander+, on battery backup, detects a power failure, it starts the generator (relay output, not X10!) and the TC+ will reconfigure everything as before because it has detected the power failure. When power comes back, my huge contactor will switch back to the main supply (50Hz), on the fly and the TC+ and my X10 modules will not even detect the interruption.
Sometimes, this glitch when switching back will cause some X10 modules to turn on, probably due to fast local control but everything works completely normal both on 50Hz and 60Hz. One day, I have to create a routine on the Timecommander that reconfigures those modules to a correct state also when power is restored. I should perhaps also try to disable local control in those modules.
Well, my pool filter makes a strange noise when running on 60Hz so I have decided not to use the pool filter when the generator is running. Be careful with bigger motors! Also the timer on the microwave owen runs too fast on 60Hz and so does the mechanical programmer on my old washing machine. The motor in the programmer probably stops and waits for different water levels and temperatures before continuing, so washing result seems to be acceptable the few times I been using the washing machine on 60Hz. Well, perhaps my wife can see the difference!