If I choose to not rewire the panel for a house that's not mine, can I still install a spa panel with the existing configuration?
You would essentially be using the spa panel as an in-line GFCI. Cord from wall outlet to spa panel, then another cord/outlet on the spa panel to your control panel.
I foresee staying in this area for a while, which is almost entirely made up of houses from the 1920s and 1930s.
Maybe I can go the 120V route with two foldback 1500W elements. I can run power from two different circuits, use the PID for one of them, but just have a switch on the panel to manually turn on the second when I need to ramp up to a boil or rapidly heat strike water for the mash. I can just swap out the existing receptacles in the house with 15A GFCI receptacles.
If you are in an area that is mostly natural gas or propane heat (like Chicago), then going to dual 120v is not a bad idea, since a lot of houses may not have a dryer outlet with 220v. If electric dryers are common, then I would probably move towards 220v.
A 3 prong dryer outlet is a H,H,N configuration. Generally speaking, it is still up to code to use, but new installation mandates a H,H,N,G 4-prong configuration. Neutral and Ground wires both provide a return path for electricity to ground. The two should be connected ("bonded") at the panel and only at the panel. That allows the ground circuit to act as a safety feature that provides a back-up return path in the event of a neutral wire short somewhere in the system - at all other times, the ground wire does not carry current.
While it may not be best practice or up to code, using a GFCI spa panel with a 3 wire configuration should work.
https://www.homebrewtalk.com/forum/...tric-brew-pot-controller.447359/#post-5735537
The primary issue with electricity is that when it goes wrong, it goes really, really wrong, and people die and houses burn down. Other than that, electricity is straightforward to work with and safe.
*I am not an electrician. Consult one.