Panel CB or fuse (for each of 3 phases used)> Contactor> Load
But it does not seem a good match to step up a 5V signal to 12V @9Amp to drive a 500A 600V 3 phase rated contactor just to 240V bulbs.... unless just an academic exercise, when a better solution is 5V signal> {opto-isolator > MOSFET driver} or all in one package > IGBT> 500A load .
Zero crossing control using LOGIC Pulse from AC zero- crossing and PIC ON/OFF output to drive IGBT.
There are also thousands of ZCS opto isolated SSR ( solid state relays) to pick from.
If academic exercise OK, but analyze costs, loads and efficiency.
Good luck.