sundance-communications.com/forum Forums Other TDM Phone Systems Other Telephones & Systems Maximum Telephone Ring Voltage?

Can someone please tell me what is the maximum telephone rms ring voltage that a PBX is allowed to output to a plain old telephone on top of the 48VDC? Is there an AT&T (or other) spec on the maximum ring voltage and tolerance?
I am designing a surge suppressor circuit for telephone lines and I need to know what this maximum voltage is. Various internet sites say 80VAC, 88VAC, 100VAC, 115VAC etc..
Thanks

Yep. We used to see all of those :-). I think the tolerance of the ring generator is pretty wide, from 70-130 volts. But for fun, try 105V RMS +/- 20V RMS.

Carl

It would most likely be totally dependent on the manufacturer. Too much would obviously burn up the card.

I'd go with 130, BUT, remember that a power line 'cross' of 120 would be tolerated. NOT a good thing, since current capacity would be 15 AMPS and UP. Most suppressors today react to frequencies outside 15-30 hertz, as well as their rated voltage! Or, in other words, 120 Volts @ 60 Hertz, would trigger the suppressor.

I don't know why you would be designing yet another surge suppressor but FCC Part 68 and TIA-470 ought to be the guiding standards for this.

While 48VDC is the most common superimposed DC voltage value for answer detection, 72V and 96V were used to a small extent on long lines to overcome high loop resistance. To what extent this is still in use is unknown. Probably very small. Much higher than 86VRM was used on frequency selective party lines with mechanically and electrically resonant ringers.. up to 150V. Again probably few such lines in service at this time.

But a very modern Lucent/Avaya made ringing generator I came across just today is rated 75-100VAC output. I don't know its intended application but it's rated 20W so it might be used on a medium sized Definity PBX or perhaps on a Remote Switch for a CO.

CO ringing supplies were usually output voltage regulated pretty tightly around 86V +/- a few percent so the 75-100V spec suggests a PBX or perhaps a Remote Switch or Subscriber Line Concentrator.