The main considerations in building a safe electric brewery panel are that relays can fail, overcurrent protection should be utilized when appropriate, and that brewing usually occurs in damp environments.
You initial step in electrical safety with brewery control panels should be the utilization of a GFCI breaker, and the proper grounding of every component in your brewery. These breakers close quickly when stray current is detected and are especially important in damp locations due to the ability of moisture to form unplanned circuits, potentially energizing unintended components of your brewery.
A breaker also provides overcurrent protection. It is important for your safety and for the protection of electrical components of your control panel that every component of your control panel (wire, relay, etc.) holds the same rating or higher of the breaker that protects it. If this is not the case, additional breakers (or fuses) should be implemented within your control panel.
Lastly, solid state relays, the core component of heating element control in electric breweries will eventually fail. When these relays fail it is possible they will do so in the open position. It is also possible your hardware may be unresponsive for some reason, or you require immediate termination of element power – such as in avoiding a boil over. As a result, you should utilize a relay to stop all power to your elements. In the case of 240V elements, this relay should terminate both hot legs of the circuit. Solid state relays produce heat proportional to the current that they are controlling. Control panel design should allow for proper heat dissipation for this reason. Overheating in a control panel can be catastrophic.
For slower switching applications such as pump or fermentation chamber temperature control, simple relays can be utilized in place of solid state relays.