Why don’t corded landline phones need to be plugged into an electrical outlet to work?
From what I remember, at each central office, there was a set of backup batteries to keep the lines working.
Doesn’t a landline phone get its power via the telephone plug the phone’s connected to? (which also carries the call signal from another telephone & of course the transmitted audio as well)
Apparently so. However the voltage is not enough to power cordless landline phones. They have to be plugged into an electrical outlet to work.
It’s more a matter of “you can’t pull enough current from the phone line to power a cordless phone without the CO thinking you’ve picked the phone up”. Basic corded phones need less power/current, so they can “parasite” power off the phone line without causing that problem, but fancy business phones (used in small businesses which didn’t have their own PBX or Centrex) would often need power adapters for the same reason.
For basic, hardwired corded phones, the power comes from the landline itself, not the power company. That said, often times the landlines are run on the same “telephone poles” as high voltage wire, so if a pole is hit and everything on it is damaged, your phone is out too. If a power station or transformer had an issue, however, your phone would continue to work.
Speaking of the term “telephone poles” that term comes from the fact that it was used first to carry transmission of phone (and telegraph before then) before electricity was widely available. The term has kind of stuck despite the fact what telephone is seldom the primary use case for those poles now. High voltage electric is always on top, then cable or fiber are often run below on newer installations. Copper infrastructure does still exist, but it’s certainly becoming a rarity.
As someone whose birth year begins with a 19, can younger people tell me: Did your parents issue you a cell phone if you didn’t have a home phone? When I was a kid, my parents had cell phones but my brother and I did not. There was an age we were old enough to be home by ourselves, but too young for cell phones, so our home phone was our primary phone for contacting our parents.
as far as i know there’s a small amount of electricity in the phone line that powers the phone, usually its like 40 or 50 volts
It’s -48VDC, standard on nearly all telephone equipment including business and enterprise scale installations and systems. The switching equipment runs off the same voltage as well. Many card based systems come to mind like the DMS-100 and 5ESS.