Had a sensor fail on a job in Wichita and realized I was using the wrong wire gauge the whole time

I was out at a house in Wichita last Tuesday, putting in a door sensor for a new system. It kept giving me intermittent faults even after I checked the connections twice. Turns out I had been using 22 gauge wire for runs over 100 feet, but the spec actually calls for 18 gauge past 75 feet. Has anyone else accidentally undersized their wire like that and fried a resistor?

3 comments

3 Comments

karencampbell1mo ago

Could the resistor have been fried from something else though?

gray_morgan1mo ago

Huh, that's actually a really good question. I've seen resistors fry from sudden power surges way more than just normal aging, like if the board's power supply cap is starting to go bad. But also don't forget about vibrations. If that resistor is on something that's bolted to a thin metal panel and there's a fan or motor shaking it all day, the solder joints can crack or the leads can snap over time. Or even worse, if there's a tiny metal fragment or dust bunny that shorts across the resistor body, it'll dump way too much current through it and poof. I'd check the whole board for any corrosion or stray junk before just swapping the resistor.

the_leo1mo ago

I had a similar thing happen in a commercial building last month near downtown Wichita. The issue wasn't the resistor itself though, it was a tiny hairline crack in the PCB trace right under the resistor. It only showed up when the board warmed up from running for a few hours and the metal expanded just enough to break the connection. Probably worth checking the board with a magnifying glass or a cheap USB microscope before you swap parts.