Below circuit is about over voltage protection related, here 2
relays (220 v) are used of 14 pins, pins # 13 & 14 of both relays are kept
in series, and both 13 pin of 1st relay & 14 pin of 2nd relay connected
direct to main AC, at the other end pins 9 to 12 of both relays connected to
one of the main input, output taken from pins 1 to 4 , Normally all pins 9 to 12 of both relays connected to pins 1 to 4,It means that in normal condition
relay will allow supply to house , normal 220 V AC voltage is unable to
energize both relay in series, but if any over voltage (double phase )
observed at the input , both relay will be energized & supply will be
disconnected .
