On Friday, November 10, 2017 at 7:20:31 PM UTC-5, Robert Nichols wrote:
On 11/10/2017 03:22 PM, Jim Wilkins wrote:
"rangerssuck" wrote in message
...

from 8KV to 13KV (half the I^^2R loss).

Ours is "19.9KV" which may be a regulatory step, otherwise why not
call it 20KV?.

Probably the same reason that telephone central offices run on 48V DC, nominal, to stay within the "Less than 50V" section of the electrical codes. (Actual voltage is somewhat above that except when actually running on battery power.)

--
Bob Nichols AT comcast.net I am "RNichols42"

I haven't done ony research on the (not THAT interesting)., but I bet that the 48V "battery" - actually -48V - predates any "Less than 50V" in the code. I spent a couple of weeks verifying test procedures at Bell Labs, where they have samples of EVERY device ever approved for connection to the PSTN. They go all the way back to stuff from the 19th century. All of them run on the same -48V system.

I have to say (probably have said it here before) that it's remarkable that you can take one of these ancient phones and plug it into a modern phone system and it still works. The same system can provide multi-megabit data service over the same wires. The Bellcore standards are pretty rigid, but allow for future improvements without obsoleting existing equipment.