What is the voltage used to ring a telephone?
According to AT&T, the ringing signal is an 88v 20Hz A.C. signal superimposed on 48v nominal D.C. supervisory voltage. However, the actual ringing signal used can and does vary greatly from one location to another.
The frequency of the AC signal is normally between 15 and 70Hz.
The interval between ringing signals is normally four seconds.
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