Why Telcom Equipments are fed with -48V

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Discussion Overview

The discussion centers on the rationale behind using -48V for powering telecom equipment instead of +48V. It explores the implications of voltage polarity on equipment performance and corrosion, as well as the consistency of power supply across different types of telecom setups.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants propose that -48V is used to reduce corrosion on metal wires, as a negative voltage relative to earth is believed to mitigate this issue.
  • Others argue that the choice of -48V applies to both remote and rack-mounted telecom equipment, suggesting a need for uniformity in equipment design.
  • A later reply questions whether the anti-corrosion rationale applies equally to rack-mounted equipment, indicating a potential for different considerations in various contexts.
  • Participants note that having a single voltage standard simplifies equipment design and deployment, as equipment may be used in different environments.

Areas of Agreement / Disagreement

Participants express some agreement on the anti-corrosion benefits of -48V, but there is uncertainty regarding whether this is the sole reason for its use in all types of telecom equipment. The discussion remains unresolved regarding the specific reasons for rack-mounted equipment operating at -48V.

Contextual Notes

Limitations include assumptions about the relationship between voltage polarity and corrosion, as well as the lack of detailed exploration into other potential reasons for the choice of -48V in different equipment types.

Who May Find This Useful

Individuals interested in telecommunications engineering, electrical engineering, and those exploring the design and operational standards of telecom equipment may find this discussion relevant.

Telco
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Almost all Telecom Equipments are fed with -48V why not +48V?
 
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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.
 
Hi
But even Telecom equipments (Rack type) are working with -48V..
Is it the same reason or any other specific reason for that??
 
Telco said:
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.
 

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