the timer should not blow. If you were to run to much current through the timer though usually 15amps is max for indoor use timers. I use 1 timer for my 300w HPS and another timer for 240watts of floro. My hps uses 6.4amps so there is room to spare on each timer. If you were to overload the circuit in the timer a fuse would take the first hit. Also i use an 36,500amp spike surge protector that all my fans, a/c, and other misc electrical run through. Yet to exceede to 30amp available on that part of my house.