RCDD · Question #128
For the telecommunications industry, the nominal operating voltage is ________ volts DC.
The correct answer is D. ?48. The telecommunications industry standard nominal operating voltage is -48 VDC, a specification defined in NEBS and related central office standards.
Question
For the telecommunications industry, the nominal operating voltage is ________ volts DC.
Options
- A
- 24
- B?24
- C
- 48
- D?48
How the community answered
(27 responses)- A11% (3)
- B4% (1)
- C4% (1)
- D81% (22)
Why each option
The telecommunications industry standard nominal operating voltage is -48 VDC, a specification defined in NEBS and related central office standards.
+24 VDC with positive polarity is used in other industries such as industrial automation and automotive; it is not the telecommunications central office standard.
-24 VDC appears in some legacy or specialized telecom applications but is not the recognized nominal industry-wide standard for central office DC power plants.
+48 VDC uses the incorrect polarity; telecom standards specify the negative rail as the supply voltage with the positive terminal bonded to ground, not the reverse.
The -48 VDC standard is the nominal DC power plant voltage used throughout the telecommunications industry and is codified in Telcordia GR-63-CORE (NEBS) requirements. The negative polarity is deliberate - it places the positive conductor at ground potential, which significantly reduces electrochemical corrosion on exposed copper cabling and connectors in central office environments. This voltage level balances technician safety with the power demands of central office switching and transmission equipment.
Concept tested: Telecommunications industry standard DC operating voltage - 48V
Source: https://telecom-info.njdepot.ericsson.se/site-cgi/ido/docs.cgi?ID=APPLIED&DOCUMENT=GR-63-CORE
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