60Hz is what we use in North America for the mains power. 50Hz in Europe. I am guessing it has something to do with this.
I am not sure but maybe for some utility applications this is needed? Or for timing sync or zero cross information? We'll check it out and let you know.
Actually, the 60Hz main input is used for 0V detection for use with triacs (for lighting control) ...
Thanks. Wasn't sure why Powerline would come into play here.