I was replacing phone lines in my house, and when I got to the terminal block in the basement, the green and red were attached to their respective posts, but the yellow conductor had been attached to a grounding post that is grounded to our water pipe. The black conductor wasn't attached to anything.
Is there any logic to grounding this yellow wire?

If I were to have the phone company put in a second phone line, that would use all four conductors, and I certainly wouldn't have a ground wire then, so I'm questioning if that wire should even be connected to ground.

Thanks for any input

 

Considering the fact that the yellow wire is not used/connected to the phone in a 1 line setup I don't see any reason for having it grounded. You'll need the black/yellow pair for a second line anyway.

 

Whay you describe suggests a ringer-connection for a "party-line" operation. We "Electrical Boys" are expert at installing the cables and completing the basic "Tip-Ring" connections, but for more expert technical advise please submit your question to the "Voice & Data Communication" Section of this Forum----Good Luck!!!