What maximum length of wire can I use to connect a push button to an Arduino? I am trying to get 8 stop buttons to cause an Arduino UNO to activate a single relay!  

The stop buttons have been placed 30' to 250' away from the Arduino uno board.

Q: How far can you go with 5v and still get signal back?

Q: Is there a way to boost the signal?
Majenko's answer is probably the safest option. There is, however,
something simpler that you can try:


Use a strong pull-up (or pull-down). Something around 1&nbsp;kΩ will
make it quite difficult for the noise to pull your signal low, at the
cost of increased current consumption.
Connect each push button to the Arduino using a twisted pair of copper
wires. This will minimize the inductive pickup effect.