Why -48 volts is used in telephone system.

FAQS.ORG makes no guarantees as to the accuracy of the posts. Each post is the personal opinion of the poster. These posts are not intended to substitute for medical, tax, legal, investment, accounting, or other professional advice. FAQS.ORG does not endorse any opinion or any product or service mentioned mentioned in these posts.

<< Back to general questions

[ Home | FAQ-Related Q&As | General Q&As | Answered Questions ]

Question by rbala
Submitted on 8/26/2003
Related FAQ: N/A
Rating:	Rate this question:
Why -48 volts is used in telephone system.

Answer by mariajohnpaul
Submitted on 10/1/2003
Rating:	Rate this answer:
i dont know exactly ,may be for good signal we have to use high voltage signal.

Answer by tom
Submitted on 10/25/2003
Rating:	Rate this answer:
The voltage drop over the copper wires from the phone company's CO (central office) can be considerable over longer distances, so a fairly high voltage is used to ensure adequate signal strength in the worst case. As for why it's 48V (as opposed to 50 or 30 or whatever), it's because the characteristic voltage of a lead-acid battery cell is 6 volts, and an eight-cell battery thus produces 48 volts. PS Ringer voltage is much higher, by the way--around 100V.

Answer by ozgurertem
Submitted on 11/16/2005
Rating: Not yet rated	Rate this answer:
The line feeding voltage was selected to be negative to make the electrochemical reactions on the wet telephone wiring to be less harmful. When the wires are at negative potential compared to the ground the metal ions go form the ground to the wire instead of the situation where positive voltage would cause metal from the wire to leave which causes quick corrosion.

Answer by Matthew
Submitted on 8/4/2006
Rating: Not yet rated	Rate this answer:
As to why the voltage is negative, do a search for "Cathodic Protection."

Answer by saravanan
Submitted on 11/23/2006
Rating: Not yet rated	Rate this answer:
Its because, negative supply prevents oxidation of the conducting copper.

Your name or nickname:
If you'd like to create a new account or access your existing account, put in your password here:
Your answer: