I bought two of these to run my mill and lathe but when I tested them before plugging them into the control box I couldn't figure out why it was making that loud buzzing/knocking noise without actually keeping either contactor closed (i.e. on). must be installed so that it is in the correct orientation, i.e. horizontal as if mounted on a panel. It's pretty cheap to me, it tells me the coil isn't strong enough to overcome gravity for a 3 pole contactor, which isn't good. I would seriouslyβ¦