How is this board switching a 24V DC relay via AC Mains voltage?
Q: How is it possible that the circuit is activating the switch, using the mains as a driver for the coil, when the coil is clearly defined for use with 24 VDC?


It's done like this:







simulate this circuit &ndash; Schematic created using CircuitLab

The coil only ever sees 24VDC here. DC shares a common potential with AC but as the circuit is encapsuled into a casing with no other outlets than the mains one, it doesn't matter.