Had a weird voltage drop on a long run for a keypad last week

I was putting in a new system at a big house in the hills, and the main panel was in the garage. The owner wanted a keypad by the front door, which was a good 150 feet away through finished walls. I figured I'd just use a standard 4-conductor cable, no big deal. When I got it all hooked up, the keypad screen was dim and the buttons were slow to respond. My meter showed the voltage at the keypad was only 8 volts, down from the 12 at the panel. I learned the hard way that on long runs like that, the wire gauge matters a lot more than I thought. I had to go back and pull a heavier 18/4 cable to fix the voltage drop. Has anyone else run into this on a big property, and what's your go-to wire for these long keypad pulls?

2 comments

2 Comments

grace_perry4421d ago

That's a huge drop over 150 feet! What gauge was the original 4-conductor cable you used before swapping it out? I've seen 22-gauge wire cause similar issues on long runs for door stations, where the voltage just disappears. Makes me wonder if there's a rule of thumb for when to jump up to 16-gauge instead of 18.

wendyc5321d ago

Yeah, that "huge drop" happens all the time with skinny wire. I always use 18/4 as a minimum now, but for anything over 100 feet I just grab 16/4. It costs a bit more but saves you a callback when the keypad acts up. The math for voltage drop is a pain, so my rule is just to go a size bigger on any long run.