I wired my own house. I have room for 240V and plans to add it for a few things, maybe, but I run heavy appliances on Natural Gas, so I haven't needed it yet. (nearly 20 years since I re-wired) My lighting circuits are 15A, but all of my outlets are 20A save for the bedrooms which were required to have Arc-Fault breakers and they didn't make 20A versions at the time. (or at least I couldn't find them)where do you live? most of the world is wired for 240.
ya 98% of outlets are 110VAC 15 A in USA. so there is little use to making anything higher wattage. but SSRs are 50-240VAC and can be had well over 15A. the ones I use are 40A
Good to know about the relay range. It may just be then that I can buy something off the shelf and re-wire it as needed for a 20A plug. I'll have to investigate that more.