An isolated power supply is used to convert 120 VAC 60Hz power from mains to 12V. A linear voltage regulator then converts the 12V to 5V.
A 5V micro-controller is then used to switch on a 12V relay (with the use of a transistor) to power an AC device.
The relay allows the AC current from the main power to flow to the device. The 12V is used to switch on the relay.
Will the use of the relay cause the low-voltage side of the circuit to lose it's isolation or does it depend on the relay?