Troubleshooting a false "Open" unit door ( PTI door alarms and GATE system, with picture!)

teamcapitola

We had a unit that kept showing as "open" in our PTI door software. The alarms are pretty simple and consist of POTs phone/data wires (RS-485) leading from door switches to various multiplexers in the facility.

If the door is open, the multiplexer sees a 5v current from the closed switch. In our case the switch was good, and aligned correctly, and the Multiplexer was functioning with other doors assigned to it. That leaves the wire leading from the unit to the multiplexer which could be broken or shorted.

Using a simple tone and probe kit, I followed the wire into the wire bundle (running along the tops of the units), across the row until I found the break.

Turns out the original installer/contractor had left the cable bundle dangling against the top edge of a roll up door barrel!

Over the years of tenants opening & closing the door had slowly abraded the wire sheathing, finally cutting a wire (and shiny copper on many others!)

I moved the cable to take the picture prior to repairing, and yes, it's now secured well away from the door!.