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-48 V DC in Telecom Equipment

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Abid Hussain Khan - 1st February 2012  (05:40 GMT)

Hi everybody,

Thanks to all for clear my confusion about why telecom equipment use -ev voltage but my question is why it is 48vDC (2*24), why not 50vDC (2*25)??

is there any restriction for DC voltage supply?

MRG - 8th February 2011  (11:16 GMT)

(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.

Lalit - 19th January 2011  (10:35 GMT)

Basically many reasons bt first is that noise and intrefrence is min at -ve supply voltage and second is that to protect from lightning

vasanth - 2nd January 2011  (07:49 GMT)

why we are using -48v...
1.pulse
2.moisture
3.earthing(lightening effects)

dextur - 21st November 2005  (00:19 GMT)

hello ranjeet,

i believe it is -48 to avoid cathodic reaction. You can read on this in the book Telephony by HARB.

Shaleen Srivastava - 14th October 2005  (08:30 GMT)

hi suku
actually this reason which i had told about the +ve supply ,told by one guy from philipines he is expert in telecom
i'll try to find ur answer and get back to u soon
can u please give me ur email id
mine is
srivastava.shaleen@gmail.com

suku - 13th October 2005  (17:09 GMT)

Hi Shaleen,

I have seen Motorola BTS , BSC , XCDRs have a positive +48V design also .

in this what will happen .

shaleen srivastava - 13th October 2005  (07:40 GMT)

Actually the earth is consider to be positive so we apply negative supply to our BTS so that when lightening occurs the charge travels to the positive terminal like earth not to the BTS. if we apply positive to our equipment then both the equipment and the earth will be connected and our instrument can be damaged during lightening
So negative polarity seperates our BTS from earth.

One more thing which i had heard is that all the digital equipments are configured to work on negative polarity

regards
shaleen srivastava
BTS Engg.
CH2MHill Communication group ltd.


srivastava.shaleen@gmail.com

suku - 12th October 2005  (12:46 GMT)

Hi,

I feel that , the power supply can't generate negative voltage .

only the polarity is changed , with respective to the chassis of the equipment .

incase of -48v system , the +ve bus bar is grounded , if is't +48v system the negative bus bar is grounded .

kat - 12th August 2005  (11:33 GMT)

hi all

ashish gohel,
noise pulse can be neg(-) also, there is no specific reason to be it pos(+).

can u explain more on your point??

-thanks

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