So it would go from the power in (receptacle male plug) to power in relay to the SSR?
Is the relay the same thing as a contactor?
contactors are relays. But they are heavy duty burly ones meant for switching on and off large loads.
You can put the contactor either before the SSR or after the SSR.
On my system, I put it before the SSR, but on the system I am helping someone else design, I am suggesting that he put it after the SSR. The reason for this is that he is building a system like yours (manual plug/unplug of the two kettles) but he eventually wants to put in a receptacle for the other kettle.
With the contactor after the SSR, then the future upgrade just becomes the dropping in of a second contactor and changing the on/off toggle switch for the contactor into an on/off/on selector switch to control which of the two contactors is enabled. The SSR feeds both contactors in that config and the selector controlls which element powered up.