Back when "Interconnect" first happened (for those kids out there, that's 1968) it was customary to have VCA (Voice Connecting Arrangements) installed and maintained by the telephone company between the CPE and the telephone company's services.
This became a "Wild West Rube Goldberg" when it came to tie lines. It was common to have 2 wire circuits morphed into 4 wire circuits and vice versa using those A B transformers and a "derived" third pair that became the talk pair. If the tech wasn't aware that there was no "hard" wire way to test the talk path, end to end, through the VCA the tech would spend a lot of time on the phone with a CO switchman trying to trouble shoot a problem through the VCA that could not be tested. When that became a nagging headache, the switchmen began to instruct the techs to test on the telco side of the VCA instead of the customer side. If the end to end tested good from site to CO to CO to site, then the tech was to replace the VCA, run to their truck and drive away, quickly.
Being on both sides of the early "Interconnect" years, I understood the frustration the telco techs had trying to deal with the VCAs and, especially, little trained or not trained "Interconnect" techs that didn't know a tie line from a shoelace. I am guessing it was around 1974 when Bell Telephone finally gave up on VCAs.
Rcaman
