Feedback requested for my circuit (automated brewery)
GND shouldn't connected to earth ground (main ground). But you can protect low voltage circuits with varistors connected to earth. In case 110V would appear on a 5V or 12V line, the varistor will clamp and trigger the circuit breaker. Use varistor with working voltage +- 2 volts above the voltage of the line.
The amperage of the main circuit breaker should be as low as possible. If you installation will never use, in any circumstance, more than 5A, then choose a 5A breaker. it will be safer.
It's much safer to use a differential breaker, for use in bathrooms, since you are working with liquids.
I would use 12V relays and valves. Less curent needed. Using a separate power supply for the relays and valves is a good idea.
I would also use as many 12V, 15V or 24V devices as possible instead of 110V ones if you can find them.
Don't use thin wires with low voltage where significant current must be drawn (&gt;1A).
Working with &quot;high&quot; voltages is more a matter of care in the montage, the quality and robustness of the connectors and the isolation. The high voltage part should be distinct and physicaly separate from the low voltage part. Don't put high voltage wires near or above the low voltage section.
Put the high voltage section in a separate enclosure.
Use only monolithic wires except with moving parts if any and the main cord if the installation has to be plugged in a wall outlet.
Every metallic part should be grounded to earth ground.