How to build a relay switch that resets when power goes out?
Typically you use a relay wired so that the live side of the switch powers the relay coil. 
the button used should be capable of powering the whole switched load







simulate this circuit &ndash; Schematic created using CircuitLab

by adding a diode the load can be isolated fronm the button allowing the use of a smaller button that only needs to pass the relay coil current (about 0.1A)