There are a couple of possibilities.
There’s a 20A wall socket from Enerwave, ZW20R, which should work as an on off control. Just be aware that like most of zwave wall sockets, only one of the two receptacles is radio controlled, the other is just a regular always on receptacle.
There’s also an Intermatic contractor module which can handle really high loads, but I think it would be overkill unless you’re looking at pool equipment or something like that. It’s also gigantic.
There are two fixture relays which would work for light or wall socket control. They would be wired into the circuit (typically at the light fixture itself). the zwave one is the evolve LFM20 which is on the official “works with smart things” list. it’s pretty popular in the community.
The second is A zigbee relay, also on the official compatibility list, from smartenIT. Intended for pool and pond equipment. Much smaller than the Intermatic, but also limited to a total of 30A between two circuits. But you can just wire it as one. This one will act as a Zigbee repeater.
Both the relay devices are on the official compatibility list:
I only know of one zwave light switch with 20 A capability, although there may be more. This one is a rocker though, not a toggle. It’s also really old – – generation 3 zwave, and we are now at gen five. HomePro ZRW103. It should work fine with SmartThings as a basic on/off switch.
So those are some options.
@Navat604 , who is a wiring expert, can say more about the wiring required for these. I just know the RF device spec sheets.