Why Telcom Equipments are fed with -48V

[Telco]

Almost all Telecom Equipments are fed with -48V why not +48V?

 

[mgb_phys]

Anti-corrosion. Originally the DC power was fed down the telephone wires to power remote equipement a +ve voltage on a metal wire encourages corrosion a negative voltage (relative to earth) reduces it.
For equipment inside the electronics rack it doesn;t really matter.

 

[Telco]

Hi
But even Telecom equipments (Rack type) are working with -48V..
Is it the same reason or any other specific reason for that??

 

[mgb_phys]

But even Telecom equipments (Rack type) are working with -48V.. Is it the same reason

Yes, you don't want to have to build a local and remote version of the same kit.
And even kit in a rack might be put out in a street corner box and fed from a central exchange.