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Global Telecom/+48 Volt and -48 Volt in Télécommunications equipements

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Question
QUESTION: Hello,

My question is what's the déférence bitween +48Volt and -48Volt in Télécommunications équipements,if there is than which is the best?

ANSWER: With telephone systems, -48V is used almost universally because of the electrochemical action that is accelerated with positive voltages, which results in corrosion. The result is additional maintenance costs, and additional service problems or outages resulting from corrosion if positive voltages are used.

Tom Smith
http://tjstechnical.com


---------- FOLLOW-UP ----------

QUESTION: thank you for your response;

I dont understand,what do you mean by(which results in corrosion) corrosion of what exactly?.

Thankyou a lot.

Answer
Corrosion of the copper. If there is any small crack or opening in the insulation, then there is a tendency of the copper to be oxidized or combined with other substances and be changed from a metal into a copper compound, thus reducing the strength and current carrying capacity of the wire, and over time causing the connection to be broken. This is the result of a chemical reaction between the copper and the substances in the surrounding earth in buried cable. Positive voltage attract the ions which accelerate the process by which copper combines with other atoms, and then increases the rate at which the connection is disrupted. By applying a negative voltage, the rate of the chemical reaction is decreased.

I hope that helps clarify it.

Regards,

Tom Smith
http://tjstechnical.com

Global Telecom

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Tom Smith

Expertise

I can answer questions regarding the telecom networks which exist throughout the world as well as requirements and approvals required for equipment to be connected to the networks.

Experience

I have been involved in product approvals for over 25 years, working both for major manufacturers, design organizations, and two major testing laboratories. I have experience putting products into countries around the world, working with various approvals agencies, and have been involved in various standards development agencies (Product Safety, EMC and Telecom). I was the Senior Approvals Engineer at the first private telephone approvals laboratory in Canada, and have been involved in the development of Industry Standards for telephone and telephone products.

Organizations
- Senior Member of IEEE - Association of Professional Engineers, Geoscientists of Alberta (APEGA) - Professional Engineers of Ontario (PEO) - Terminal Attachment Program Advisory Committee (TAPAC) which is under the jurisdiction of Industry Canada (Department of the Gov't of Canada) - Canadian Standards Association - Institute of Electrical and Electronic Engineers (IEEE) - Product Safety Engineering Society - Former Approvals Liaison Engineer (ALE) for the British Approvals Board for Telecommunications (BABT) - Former ALE for AUSTEL (Australia) - Only ALE Appointment outside of Australia - Regulatory Affairs Professionals Society (RAPS) - Registered Consultant to the Hong Kong Telecommunication Authority

Publications
Suggested Design Techniques for Telephone Equipment Requiring Canadian Certification Presented at the International Conference on Consumer Electronics (ICCE), Chicago, Ill.(1985). Paper published in IEEE Transactions on Consumer Electronics.

Education/Credentials
B.A.SC (Electrical Engineering)

Awards and Honors
- Only Approvals Liaison Engineer (ALE) ever appointed by AUSTEL (AUSTEL is no longer the authority in Australia, and the ALE program was also replaced in 1997) - Former Deputy Approvals Liaison Engineer appointed by the British Approvals Board for Telecommunications (BABT) - Elevated to Senior Member by IEEE - CSA Plaque given for 20 years of Services in standards development

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