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Why is -48v used in Telecom?


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Answered 2007-12-06 03:30:41

(i) Positive voltages cause comparatively more corrosion in metal than negative voltages. (ii) Negative voltages are safer for human body while doing Telecom activities. (iii) Lightning may cause positive voltages in the equipment circuitry. In that case, negative voltages (lack of electrons) neutralize positive charges and prevent excessive heat. (iv) Negative voltage is safer for long telephone line for transmitting power trough it. The reson for electing -48V in reference to ground is to avoid the nasty galvanic effects in telephone cabling. +48V would have nastier effect on wet cabling.

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48 volts is a convenient safe voltage to use, and telephone systems use a positive earth connection to minimise electroytic damage ot cables.


It was originally supplied by a large bank of lead-acid batteries, 24 cells in series gave 48V.


In earlier days of telephone networks, 48V DC was once found to be suitably high to be able to make telephone work on long telephone lines and still low enough not to cause serious danger if somebody touches the telephone wires. Telephone central offices (exchanges) so started using 48V DC. Even when newer automatic exhanges were setup, they were designed to make use of existing 48V battery sets and arrays which were available with telecom service providers. This legacy design practice has been continued and over many decades all new telecom devices have been designed to work with 48V. The positive grounded or -48V system is also from telephone history. The negative voltage on the line was better than positive to prevent electro-chemical reactions from destroying the copper cable quickly, if cables get wet Ans- It is because of cathodic protection. It reduces the sulphation on the battery terminals.


For better Noise clipping we use -48v as all the noise are on +ve side


In a 48V DC system you ground the positive to 0V so the live wire will be -48V.


always think of any supply system so : RED = MOST POSITIVE BLACK = MOST NEGATIVE in a telecom system the -48V supply is refferenced to ground and earth, so the supply wire is NEGATIVE, this means a DC supply most positive signal the RED wire, go to EARTH = ZERO, the BLACK wire is the MOST negative, so in this case it is -48V


because the termination and relays in side the telecoms penal needs for DC supply to continues the protection equipment and relay and purpose of telecoms


A 48V power source is used to power an SDH pump to allow for sufficient electricity to keep the motor moving at maximum efficiency. These pumps are used in a variety of agricultural and industrial applications.


because in this voltage harmonics are not present


in order to stop the oxidation process


-48V is used in the telecommunication equipment. The source of the -48V is a bank backup batteries that are always kept charged in the event of power loss. The typical range of voltage is -36V to -60V in this application. Why negative voltage is used is probably tradition as the modern power supplies that use this voltage are isolated and run the same as long as the positive terminal is 48V above the negative terminal.


breastsize48v.brazili.legnica.pl this site says 48v whatever that is. breastsize48v.brazili.legnica.pl this site says 48v whatever that is.


British telecom is a old name of BT which deals in telecom and broadband


Telephones run on voltages from 36 v to 50 v. It's a safe voltage and high enough to allow phones to work 2-3 miles from the nearest exchange (switching centre). It is common to earth the positive side, for historic reasons which are probably based on minimising electrolytic damage to the cables.


The symbol for Telecom Argentina Stet - France Telecom S.A. in the NYSE is: TEO.


The main telecom provider in the UK is British Telecom. However - cable companies such as Virgin and others, also supply telecom services.


Vodafone is way better! Telecom sucks! Telecom always breaks down!


The transistors revolutionize telecom. industry 1. Affordable 2. Easy to used 3. Used only small space 4. Many uses 5. Not easily destroyed


yes . . . . telecom sucks


Telecom Italia's population is 84,200.


Telecom Italia's population is 2,010.


Globe Telecom was created in 1935.


Iowa Telecom was created in 2000.


Telecom Plus's population is 2,012.


The population of Telecom Plus is 550.



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