I've designed a board with a few relays that switch 120VAC. I have the normally open side of the relay connected to a current limiting resistor and opto-isolator. Do I need to worry about single fault failure for safety testing? If so, can I just put two resistors in series?
I'm working with a system that requires me to read 120VAC inputs on a pivot irrigation system. The wires travel 1/4 of a mile. Occasionally on the line I am reading, the voltage is 65VAC instead of 120VAC. I believe this is an induced voltage because of the length of the wires. I only want to...