light electrical

Installation could not be done exactly as directed by the instructions. My switch had only 3 wires available. 1)The bare ground wire. (Which goes under the green screw on the timer). 2) The hot wire (check with a meter which one this is and don’t trust color as mine was reversed white being hot but other switches in the box black was hot. Electrician mistake) this connects to the black wire of the timer. 3) a wire that goes to the fan fixture. (Which is what is connected to the Red wire of the timer)
The directions call for a white wire on the timer to be connected to a common wire in the box. A common wire goes back to the electrical panel and is attached under a screw on the common bus bar.
This wire is often not present in a switch box and this timer will not work without it since it needs all the time power for the electronics to work. Just a hot wire is not enough. The solution is to connect the white common wire from the timer under the green ground screw giving the timer power. Ultimately the ground wire goes back to the panel and is bonded with the common wire in the panel so essentially for this almost no current draw connection it works just fine. A short to either the white or the ground of the hot wire will cause breaker to trip.