Originally Posted by nitrousjunkie
The SSR will control one leg of your 240 line, so it will only see 120 going through it. It does not convert ac to dc power. Your controller sends a dc signal to the ssr. Think of the ssr as a very high speed relay.
Not true - the SSR needs to be rated for at least 240 VAC. This is because even if you use two, one to control each leg, slight timing differences could cause one to "see" 240 VAC. And 240 VAC for even a very short time will blow out a 120 VAC rated SSR.
Also, for 4500 Watts @ 240 VAC you need a SSR rated for at least 20 Amps (4500 / 240 = 18.75). A 40 Amp SSR is over kill. a 25 or 30 Amp gives you some safety margin.