Richard Crowley says... said:
And it doesn't really matter anymore anyway. All modern phone
equipment will operate properly regardless of the polarity. The stuff
that doesn't isn't properly designed or assembled. Note that it
Ahhh... wait a moment. I understand you're referring mainly to
"modern" phones, but I still take issue with that statement!
The older Bell System (Western Electric) phones from the 70's-
early 90's are most certainly "properly designed and assembled" (as
evidenced by their amazing service life -- my key system has been going,
more or less continuously, for 20+ years), but earlier TouchTone sets
will not dial out with reversed polarity.
In fact, it was common practice among telephone installers to flip
the polarity on the connection to sets that the owner did not want
people to be able to dial out on.
was (is?) common to reverse polarity to indicate certain things
like call completion.
I've not heard of RP being used to indicate call completion
(perhaps someone else has?), but I will say that it is common for most
central offices in the U.S. to drop the line battery altogether for
about two seconds, if a phone goes off-hook and you don't do anything
for 30 or so seconds.
The reason for this dates back to the first key telephone systems,
developed in the 40's. If a line were taken off-hook, and then
immediately put on hold, or if a caller on hold hung up and the line
went back to a dial tone state, AND the hold bridge failed to release,
it could tie up common equipment at the CO.
That battery drop I mentioned above will force the hold bridge at
the customer's end to release, thus clearing the line. Even the most
modern of electronic CO's do the battery drop thing to this day.
This has been your Bell System trivia for today. We now return to
your regularly scheduled Schickelgruber.
