Thread: Telephone and power supply

hi...

Can someone tell me..

The operation of a telephone does not depend upon the power supply.Even if the power is out, the telephone still works.How?

Originally Posted by mohana

hi...

Can someone tell me..

The operation of a telephone does not depend upon the power supply.Even if the power is out, the telephone still works.How?

The telephone line has -48V when idle and +90V when ringing. In other words, the power is being supplied at the Central Office switching. If the power is out, the CO has back up batteries and gas-powered generators to keep the power on the line.