Telephone voltages

Thread Starter


Joined Apr 19, 2007
First and foremost, I am enjoying the site and find it a tremendous help in reminding me and advancing my understanding of electricity. It did, however, come to my attention that the voltage listed for the telephone system is incorrect. There are 3 conditions that the system operates in. Ringer, Standing and "In Use". You stated that the ringer voltage was 48 VAC. In actuality, the standing voltage is 48 VDC, the ringer voltage is, as I believe, 135 VAC and the "in Use" voltage is 9 VDC. There are other considerations to mention as well. In circumstances where there are not enough facilities to support demand, the telephone companies will muliplex the phone lines with a 135 VAC carrier. Also, one of the methods of servicing the phone system is the use of what is called a "Breakdown" test where a high voltage is applied to the system. Although there is a great amount of care used when breakdown equipment is used (similar to lock and tag) but as always consideration must be given that the safety procedures might not always be followed/understood 100%. I thought that you'd like to know and hope this info is useful.