Bad Levition patch cables cause hours of headscratching


Active Member
I just wanted to share this experience with my fellow Cocoontechers. I recently purchased two new 3 ft Leviton Cat5e patch cables at my local Home Depot and used them to connect my keypads to the Elk DBH. My setup is a little different: the runs of in-wall cat 5 wires that go to the keypads terminate at punch down jacks in the wiring closet, then patch cables connect the punch down jacks to the DBH. Once I put the new Leviton patch cables in my system, the keypads showed faults. It turns out that the Leviton patch cables while showing conductivity on the cable tester have too high of impedence for the RS-485 bus. The new Leviton cables with their high impedence essentially terminate the bus so that any device on the DBH downstream from the Leviton cable is out of the loop. Has anyone else experienced this? For a quick fix, I scavenged some old cat 5 cables that are twice as long, but they work.

The moral is: even though a cable shows good on the cable tester, it may not be good enough for the RS-485 bus. Or more likely my cable tester is not good enough. Nor is Leviton's quality control.