48 volts is a convenient safe voltage to use, and telephone systems use a positive earth connection to minimise electroytic damage ot cables.
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
dc
To prevent the equipments from lightning strokes. Because the cloud is negatively charged at bottom it requires a zero or a positive potential to discharge, and it selects the ground (Zero potential) to discharge. If the Telecom Equipments are fed with positive the cloud will choose the low resistance tallest positively charged Antenna's to discharge, this could damage the entire setup of Telecom equipments. So the Telecom equipments are fed with Negative supply Voltage.
A telecom shelter contains transmitters inside.
Doing the job correctly ! There's no point finishing the job quickly - if the equipment is not wired correctly.
It was originally supplied by a large bank of lead-acid batteries, 24 cells in series gave 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
dc
Voltage is dependent on a reference. If I have a 12 volt battery, and ground the - side, it is 12 volts to ground. If I instead ground the + side, it is -12 volts to ground. -48 volt telecom equipment is simply referenced to ground "upside down" or backwards, giving it a negative sign.
-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.
There are many ways in which one can acquire telecom test equipment. This includes sites such as Amazon or eBay as well as specialist firms such as RS Online and Sunrise Telecom.
its operation and maintenance equipment
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
This voltage is supplied by large banks of lead-acid batteries at the central office. There are 24 cells in each battery, giving 48 volts. Grounding the positive battery terminal makes the delivered voltage negative. Batteries are used so the system can keep operating (for a period of time) during a power failure, so that emergency and other important calls can still be made.
In a 48V DC system you ground the positive to 0V so the live wire will be -48V.
Zhong Xing Telecommunication Equipment (ZTE)
for A+: very good