POTS – Plain Old Telephone System https://infogalactic.com/info/Plain_old_telephone_service is something we end up taking for granted.
Recently I had some questions on voltages at rest and ringing, and found this reference:
My question also had to do with REN (Ringer Equivalence Number) issues. A REN is the amount of AC current that’s used by an old Bell type 2500 set with mechanical bells.
Typically you get 5 REN or more, but lots of issues can make it less, attenuated, or as it was in my research case unexpectedly “all used up” by gear that needed more RENs each than the labels added up to.