why -48V DC is used in telecommunication systems?

Answer 1

Output voltages used are: 5 vdc,12vdc,15vdc,24vdc and 48vdc.
Except for the five and fifteen vdc, we find that the other voltages are lead sulphuric acid cells which is 2vdc. so dc batteries determine this type of dc output.

Answer 2

48 volts is chosen, as being high enough that operating currents can be low, and sufficiently low to overcome some accidental ground faults.

Telecommunication systems use ground (earth) return, Currents flow through a single conductor, with return through the earth. -48 volts means that the positive electrode of batteries is connected to ground. Any leakage from the negative side to ground results in sacrificing the object to which the circuit is grounded. With copper conductors it also causes corrosion that forms a diode. The diode is such that it opposes further current flow. The reduction in current enables circuit operation to continue.

If the negative electrode of the battery were grounded instead, accidental grounds would hasten deterioration of the conductors.

Answer 3

The negative is all based on reference. 48 V DC is the same thing as - 48 DC it's just depends on how you connected your probes. The 48 is probably because of some standard; designed for minmal propogation losses, and reduced noise interference; while avioding the need for heavy insulation.

Answer 4

hi
All the equipments used in telecommunication systems are desinged to operate on 48V .But as simple it is not harmful to repair a damaged equipment which is on 48V.
Not harmful zone is --0 to 60V.

Answer 5

telecommunication systems intigrated exchanges works on this rating only. if different rating is used lots of disturbances in terms of voice clarity arises ... so by trial and error this rating is accepted.. i think so