SPA 112 voltage on line

[JCloGca]

Am using Cisco SPA 112 telephone adapter with a gate intercom system. The gate call box no longer works. When tested, it is showing voltage on the phone line from the call box. When the SPA 112 is removed the voltage goes away. Why is there voltage on the line when the Cisco phone adapter is employed and how do I make this work?

[Dan Lukes]

Well, it seems you doesn't understand how the phone analog line works. CCS is not good platform to teach basics, but in short, there's exchange or other call control device on one end of analog line and just phone on the other end.Call control device provides power for phone over the line

SPA112 is call control device here and intercom is phone in your particular environment.  Thus SPA112 provides power and when removed voltage goes away. It's not bug, it's how it works.

Sorry, I don't know why you system doesn't work. You provided no details related to the issue, so no way to analyze. Learn how POTS lines works, then check your system again for differences.

[JCloGca]

Dan,

Thank you for the reminder. Is it normal for that power to be about 35 volts AC?

[Dan Lukes]

It depends. AC should be present only during ringing time. To be exact, AC is superimposed on DC. Can you voltmeter measure it correctly ? If your voltmeter measure just AC part, then ~35V sounds OK - assuming it's ringing and there is no load connected.