In this particular case, it was a guest room control solution consisting of DIN rail mounted TRIAC dimmers 0-10V dimmers and other line-voltage & dry contact relays. Backbone was an RS485, 4-conductor bus. Yes, those components can produce various harmonica and frequencies, however they were tested extensively in a lab in various configurations. Each configuration varies slightly based on room layouts and number of zones, and obtaining UL-listing for every possible permutation becomes ridiculous (IMO).