When testing dial tone on a POTS line with the phone on the hook, what reading should the technician expect?

When testing dial tone on a POTS line with the phone on the hook, what reading should the technician expect?

• A. 12V to 24V DC
• B. 24V to 36V DC
• C. 48V to 52V DC
• D. 60V to 70V DC

Answer: (C)

POTS lines are powered by a central office supply that provides a constant DC voltage to the tip-and-ring pair. When the phone is on-hook, almost no current flows, so the line voltage stays near the nominal value. The expected reading between the line conductors is about 48 to 52 volts DC. Values outside this range suggest a line fault or abnormal conditions, while voltages much lower (12–36 V) or much higher (60–70 V) are not typical for a normal idle POTS line.

POTS lines are powered by a central office supply that provides a constant DC voltage to the tip-and-ring pair. When the phone is on-hook, almost no current flows, so the line voltage stays near the nominal value. The expected reading between the line conductors is about 48 to 52 volts DC. Values outside this range suggest a line fault or abnormal conditions, while voltages much lower (12–36 V) or much higher (60–70 V) are not typical for a normal idle POTS line.