Is it compliant to tap a 120vac outlet from the 240vac circuit? Or does this split have to happen inside the appliance/control panel? Could the box at the end of the conduit have a 3 prong 240vac outlet and a 120vac outlet both derived from the 4 wire line? I could run a separate 120vac line from a separate breaker at the box but then the question is can this wire be housed in the same conduit as the 240vac wire? I do need both. 240vac for the bk element, 120vac ~20amp for an element in an hlt, and 120 (ultimately 12vdc) to power the controller.
My original plan was to run the two separate. Come out of the wall into a junction box with two conduits along the wall to a box at the end with both outlets. Obviously I'm trying to cut costs so if I can eliminate a conduit and put both lines in one, cool. If I can only run one and split it at the end into two outlets, even better.
BTW thanks for the help. I'm sure this comes up a lot but at least I'm not asking why my airlock isn't bubbling after 24 hours.
You're overthinking this. Buy the 50 amp spa panel from Home Depot, it comes with a gfci breaker 240v in it. This is the cheapest way to get a gfci breaker and it comes with a panel to boot.
Then put either a 50 amp or 30 amp breaker in your main box (I went with 50 but I have a 150 amp main so I had plenty of spare current - I don't anticipate running the water heater, range, dryer, and brewery at the same time).
Next, run some romex cord in a conduit to your spa panel, you want 4 wires, not 3 so you can have both 120 and 240v in your control panel..
Then install a 240v 4 wire outlet from (or in my case - 'on') the spa panel. Now you run a 4 wire range/stove plug from that outlet to your control panel. I went with a sturdy plastic tool box from lowes, it was $20. I prefer plastic to metal because drilling metal sucks as I found out when mounting the outlet on the actual spa panel itself.
Once inside the box you can split up the current as necessary but fuse it down first. At a local true value hardware store I found a terminal block with the fuse posts built right in. I ran one of the hot lines to this block and then ran all my 120v connections off of that (fused down appropriately). I used 14gauge wire to route the 120 around the box and used 8 gauge for the non fused stuff.
So one hot wire goes right to the switch, contactor, element or whatever. The other goes there as well but makes a pit stop first at the terminal block where you branch off your 120v stuff. I installed a 120v outlet into the side of the toolbox so I could plug in my HLT stirrer and my single pump. I also installed 2 240v 3wire outlets on the box so I could plug in my 2 elements. I wired my elements to some dryer cord (which is 3 wire, rated at 30 amp).. I then plug these into the outlets on my control panel when ready to brew and use a switch and contactor to switch between the element in the brew kettle and the element in the HLT (the switch switches between outlet 1 and outlet 2).
Note, the 5500w camco elements I and others are using cannot both be run simultaneously on a 50amp circuit, it's still 1 at a time. So you really don't gain much by going much by going 50amp over 30amp.. but I did because I could, it didn't cost much more, and it gives me more room for future expansion.
There's a really nice diagram by PJ here that I followed (minus 1 pump).
https://www.homebrewtalk.com/f170/simple-eherms-following-pjs-diagram-w-only-1-pid-221403/
You can also get all the switches at lowes or radio shack. I didn't see a need for fancy lighted push buttons from automation direct when regular old bat switches work just fine. I would also suggest that you choose switches which require circular rather than rectangular holes since that makes installation a snap with a drill.