More safety: always have physical NC relay in series with SSR for any AC application. SSRs are super fun and useful. They are quiet, can be switched 100 times

More safety: always have physical NC relay in series with SSR for any AC application. SSRs are super fun and useful. They are quiet, can be switched 100 times a second if you want more than just on/off control for your heating element and they won't wear out. But they also leak current keeping the equipment under AC voltage even if not powered and have nasty fault mode where they just fuse and conduct as a very efficient short. The physical relay fixes both problems. I typically have current sense on SSR output so that my controller can compare output from SSR with what was supposed to happen and signal fault if the SSR becomes a very good jumper. So the SSR is only ever connected when the controller decides it should.