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@munguti-MnxkmE • Nov 3, 2010
The more positive wire is grounded, so that the wires are at 0 V and -48 V with respect to earth ground. The 0 V wire is at the same potential as the surrounding earth, so it corrodes no faster or slower than if it were not connected electrically. The -48 V wire is cathodically protected. This means that in the event of minor damage to the insulation on a buried cable, both copper conductors will be unaffected, and unless the two wires short together, service will not be interrupted. If instead the polarity were switched, so that the wires were at 0 V and +48 V with respect to the surrounding earth, then the 0 V wire would be unaffected as before, but the +48 V wire would quickly be destroyed if it came into contact with wet earth. The electrochemical action would plate metal off the +48 V wire, reducing its thickness to the point that it would eventually break, interrupting telephone service. This choice of polarity was not accidental; corrosion problems in some of the earliest telegraphy systems pointed the way.sundar_pmsWhy do the telecom transport equipments (like SDH) use only -48v or -24v dc?
@sundar-pms-t71V1P • Nov 5, 2010
@munguti-MnxkmE • Nov 5, 2010
