The voltage of a home phone line in the United States is typically 48 VDC.
Home Phone Voltage Explained
Here's a breakdown of the voltage involved with home phone lines:
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Normal Operation: The voltage present on a standard phone line when the phone is on-hook (idle) is approximately 48 volts DC (VDC). Some countries may use 50 VDC.
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Ringing: When a call comes in, the telephone exchange sends a ringing signal, which is a much higher AC voltage (typically around 90 VAC) superimposed on the DC voltage. This is what makes the phone ring.
Phone Line Power
A unique aspect of telephones is that the same wires used for signal transmission also supply power to the phone. The telephone exchange provides this power. This allows basic phones to function even during a power outage. More modern phones and cordless phones may require external power, but the basic phone still gets its power from the line.
Key Takeaways
| Feature | Description |
|---|---|
| Idle Voltage | 48 VDC (in the US; some countries use 50 VDC) |
| Ringing Voltage | Approximately 90 VAC superimposed on the DC voltage |
| Power Source | The telephone exchange supplies power to the phone through the same wires used for signal transmission. |
