I have some Z-wave light switches that I want to install; below is a link to the diagram for the light switches. Basically I can have all the wiring completed minus the neutral wire for the switch at the bottom of my steps. It will be harder for me to get the neutral from the light than run it in the basement. I have a junction box that is close (4ft compared to 100ft) but it's the living room circuit. Is there anything wrong with tying the light switch that needs the neutral to the living room neutral, based on the wiring is 12/2 and the breaker is the same amperage?
If you're in the US, see National Electrical Code (NEC) 300.3(B).
This other answer explains one reason why this code rule exists.