How come red and green telephone wire is 1.5 volts only coming from wall adapter?

The red and green telephone wires typically carry a low DC voltage of about 1.5 volts from the wall adapter because they are designed for specific signaling and power requirements in telecommunication systems. This voltage is sufficient for powering devices like telephones, which use low power for operation and signaling. The low voltage also minimizes the risk of electrical hazards and interference with other electronic devices.