atcomsystems.ca/forum Forums General General Telephone & Systems Information reverse polarity

hi guys, i just new here.
well i know i found good technical website for talking phones.
i have question and still can't answer until now. can i know in detail what is mean by "reverse polarity"? and what it use for, how the mechanism work?

thanks
Cronos

Sorry, Cronos, please fill out your complete profile with the correct information and then we can better determine how to help you.

Reverse polarity is, well when the polarity on the pair is reversed. Normally tip is positive and ring is negative.

As far as a POTS line is concerned polarity means nothing today, phones will work just fine regardless of the polarity.

In the early days when touch tone was introduced and when phones were hard wired without modular cords, if the polarity were reversed the touch tone dial on those old phones wouldn't work. No mechanism here, you just had to get it right or the dial wouldn't work.

Other than that the only thing I can think of that it was actually used for were some old public pay phone that used reverse polarity from the CO for a function and then there were burgler and fire systems that would reverse the polarity on the dry pair back to the monitoring company on alarm. Just a form of signaling. Don't see any of that any more.

I can't imagine why you think there is more to this than that and why we would know something about talking phones. :shrug:

-Hal

I have gotten to the point where i now consider myself an expert in the non talking phones...next up...the talking ones!!

actually it was only the WE tt dials that where polarity sensitive , the AE tt dials had polarity guards built in

a lot of modems where polarity sensitive also ( I know Hal doesn't mess with that stuff )

Analog DID is polarity sensitive, still...

Some door phone/controllers are polarity sensitive, at least the one I was troubleshooting last week was.

Back in the SxS days here line polarity always reversed on the originating line when the called party answered. Relays in the final selector (= U.S. connector) reversed polarity to signal answer supervision back to earlier stages to start metering, and since talk battery for the line was supplied from the connector's transmission bridge right back through the switching train, it means that the polarity reversed all the way back to the originating subscriber's line.

It was of no consequence most times, but the post-payment coinphones which were in service in the 1960s-1980s period used the reversal to operate a solenoid which opened the coin slots, thus preventing anyone from inserting coins before the called party answered.

The reversal on answer supervision was carried forward to TXK and TXE for compatibility, but is no longer the norm on our digital switches, although I believe it can be ordered as a special option.

It was also important to get polarity correct on party lines, since one party used ringing and ground-start on the tip side of the line, the other on the ring side. A reversal would result in the phone ringing with calls for the other party, and in outgoing calls being billed to that other party.

What Paul said plus the reversal in the SXS office passed to the XBT office on a toll call to start the CAMA (billing) equipment.

Polarity reversal was used as a method to effect toll-restriction. On DDCO trunks in various dial PBX's (PABX's as non Bell companies called them,) the CO trunk equipment portion could be optioned for battery reversal after the last digit was dialed, if the call was a toll call. This reversal operated the TS relay in the DDCO plate at the PBX, causing the call to be instantly terminated and routed to Tone Busy.