Like the phones that have a special plug and everything, the cord one still work when the electricity is out and they don’t seem to have batteries in there, so how and why do they still work
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Batteries is the answer, i did a tour of am exchange about 20 years ago and they still used open wet cell batteries.
Lead acid chemistry batteries have a voltage of ~2V, car batteries have 6 of these in serial. Capacity comes from the lead plate service area so they are big round drums.
In the exchange 24 were lined up in series to provide 48V and multiple strings to provide. This filled an entire room and due to the nature of them they generate hydrogen which leads to a very flamable enviroment that needs to be well ventillated else they go boom. These days sealed cells are used in 4x12v battery strings.
The reason for the big strings is to provide the amperage, which while its low per line, its a lot of phone lines per exchange. The big amperage led to busbars that if you drop a spanner/screendriver on will flash vaporise/melt/arc. While ive not seen this i have had stories from guys that worked in exchanges in south africa that had a little less regulation than Australia.
48V is still used quite heavily in telecommunications big core router/switches as AC powersupplies dont go big enough
I’d love to see the submarine cable landing stations that provide several thousand volts to the submarine cables.
(I work in telecommunications)
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