How many elements do you plan to have running simultaneously?OK. How this kind of setup would change the wiring diagram presented in the first page of this thread ?
I only have a single 20A, 240V circuit so I only run one element at a time...
You really only need one PID if doing it that way, for the HLT/HERMS/RIMS.
Once you complete your mash/sparge & transfer all to the brew kettle, you power up the BK element for the boil. I just unplug my HLT/HERMS element & plug in the BK element.
What I have found to work best is a single PID fed via a probe on the output of the HERMS prior to returning back to the MLT. I also have a dial temp gauge on my HLT water & the MLT. That way I can compare all three temps relative to one another. They are typically always within one degree of each other. I originally tried to measure the mash temp coming out of the MLT on it's way back to the HERMS but it resulted in much wider temp variance between the MLT & HLT.
I also have a probe on my BK but you don't have to have one for the sake of the boil.. Just set the PID to manual mode. 212 degrees & control the boil via manipulating the duty cycle output of the PID.