PCB designing consideration of high speed (0.5 Hz) relay load switching
When switching the mains (230 VAC) to a load your most important concern is:
How long will the relay's contact last?
Each time you switch the mains, the energized contact of the relay will create a small electric arc in the air that goes to the non-energized contact. That arc shortens contacts' life.
To prolong relay life you might want to buy relays with silver plated contacts:
https://eu.mouser.com/Electromechanical/Relays/General-Purpose-Relays/_/N-5g36?P=1z0x3vzZ1yvsbagZ1yf6b2w
There's another and I think more interesting idea to prolong contacts life. It's called &quot;zero crossing relay switching&quot;
Switch the mains when the 230 V voltage crosses the time axis. Take a look at this Microchip application note:
http://ww1.microchip.com/downloads/en/appnotes/90003099a.pdf