110V / 33K = 3.3mA. I would guess that you could probably drop the 'sensing' line onto ground and at most (assuming your 33K is wired up right), you should only get 3.3mA of current. But to be safe, throw a good ZENER in there, maybe a couple of them, one at a high-ish voltage and one a few volts above your max at the PIC....and a small fuse inline with everything else just in case everything else goes bad and call it good.