Electrical – Isolating a bulb from stairwell timer

I'm surprised that the box or paperwork that came with the switch didn't have instructions, so here is my advice (25 years as an electrician): The black wire goes to the hot bundle, the green wire is ground, and the blue wire goes to the light that is being switched. If there is a pig-tail that acted as an individual wire to the old switch, you can either keep that and attach the black wire to it, or remove it from the bundle and connect the black wire on the switch directly to the bundle.

As a way of checking what I am telling you, on the switch itself, there may be some labels for each of the wires (the black, blue and green wires). Typical labeling for the 'hot' wire is: "Hot", "Common", and "Line" Typical labeling for the switched wire is: "Load", "Line", or "Switched"

Note that in my experience, whenever the label for the Hot wire is "Line", the switched wire is never called "Line" -it is almost always labeled "Load" (which is more accurate -but let's not argue semantics).

Good luck and happy wiring!

:) Greg

Presumably the black and red wires are the hot and switched, corresponding to your current switch. If the box is gounded, that one's good. The issue (depending how the box is wired) may be that the timer needs a neutral connection, and if the box only has "switch loops" run to it it may not currently HAVE a neutral wire - in which case you need to get one there.

Now, when you say that there are 5 cables in the box, do you mean 5 multi-wire cables (black-white-bare/green) except one of them is red-black-white-bare/green and there are a lot of white wires connected to each other? If so, it's your lucky day, as one of those white wires will provide your neutral connection. Avoid white wires that are connected to switches, as those probably are NOT neutrals.

A picture would help a lot, but that's my educated guess, if you are using "cable" in the usual sense, as opposed to confusing it with "wire."