That's a good rule of thumb. I noticed that the diagram says to use the right voltage for country's mains voltage. My question is, if I get a 240v heat pad when my outlet is 110v, will the solid state relay "boost" the power similar to what an automotive relay does? or should I just go with a 120v heat bed. Ideally I'd like to get the 1200w heat bed that I've seen that is 240v because that would give me .75w per square centimeter which will get the bed hot enough for pla, and also a little extra for fast heat up time. I have searched for a 1600 watt one which would give me 1 watt per square centimeter, but I came up with no results. I would like some input because I am about a stone's throw away from having all the components I need to complete my build.