< > When a phone is on-hook (hung-up) there is a 48V potential on the line. < > When the phone is ringing, there is 90v (nominal) AC on the line during < > the ring cycle to activate the ringer. When a phone is off-hook (you're < > talking) there is 12v on the line. the voltages are wildly approximate. It's current that does the work! On hook is sensed by some current flowing and the threshhold is about 5-10ma may be more. Ring is ac coupled but the voltage is set so the energy level of the ringer is met despite the loop (line) resistance. the only one that was nominal was onhook of ~48v. Allison