sundance-communications.com/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems 551B KSU Ringing Issue

One of these days I'm gonna learn and not answer any damned questions. Then all the 1A2 wannabe's can go find their answers somewhere else. I'm only an old worn-out expert in one narrow, useless, obsolete area of a vanishing industry, but I still would like to get some respect.

You're right bill I once had a "tech" install a new line , that left a note saying my service was on the "purple gray wires" of course after 30 years I felt I could figure this out.

From the manual. Maybe his outlet wasn't grounded?

3.14 Any installation of the 550/551-type KSU should be grounded and protected in accordance with the requirements in Section 518-010-105. The frame of the KSU power unit is grounded through the third, or "green," wire of its power cord. The local or circuit ground of the power unit, which is the positive side of the de output, should be connected to the same ground as the system protector. Do not connect circuit ground and frame ground together.
3.15 The 550/551C KSU has an external grounding terminal, labeled LOC GRD, on the front of the backboard above the interrupter. It is wired internally to the power unit ground circuit at the G± terminal of the connecting block. Connect this terminal to protector ground with a 14-gauge wire brought through one of the cable clamps below the connecting block. On 550/551A and B KSUs (MD), a multiple-post grounding terminal is located on the top of the connecting block.
BSP

No, grounding never had anything to do with the proper functioning of 1A2 equipment except for CO ringing, which was dependent upon the card(s)used. The hold function was accomplished through a careful balance of the A Lead and the line's loop voltage/current. If all of those were not within specification, then anything could happen, or not.

Thanks Ed I haven't touched 1A2 in a long time and when I did in the '80's it was primarily ITT and we always cold water grounded them. Never had many issues with them either except for maybe hung up 401a relays.

John: That's why WE's 551C was designed. It overcame many of those grounding issues, primarily because they realized that grounded ringing was becoming a thing of the past. Since the 400G KTUs came out around the same time, they thought they had it all licked. Or so they thought......