1. Prevention of Electrochemical Corrosion (The Most Critical Reason)

Physical Principle: In humid environments, metal conductors carrying a positive voltage (positive pole) are more likely to attract negative ions from the air, leading to electrochemical corrosion and causing cables and terminals to gradually rust and break.

System Design: If the positive terminal of the power supply is grounded (i.e., set as a 0V reference point), then the entire casing, cabinet, and wiring of the communication equipment will transmit a negative voltage (-48V).

Effect: Negatively charged metal conductors are less prone to electrochemical corrosion. This is crucial for communication base stations and equipment rooms located throughout the country in diverse environments, significantly extending the lifespan of equipment and cables and reducing maintenance costs.

Simply put, grounding the positive terminal "immerses" the entire system in a negative potential, thus protecting metal components from rusting.

2. Reduction of Noise Interference

Communication equipment requires extremely high power purity. Grounding the positive terminal provides a stable and clean "zero potential" reference ground for the entire system. This unified ground reference helps reduce noise interference caused by stray currents and ground loops, ensuring the quality of communication signals.

Compared to leaving the positive terminal floating or grounding the negative terminal, the positive terminal grounding scheme performs better in terms of electromagnetic interference immunity.

3. Perfect Integration with Battery Systems

Communication equipment rooms and base stations are equipped with a large number of lead-acid batteries as backup power. A standard lead-acid battery has a nominal voltage of 12V.

Connecting four 12V batteries in series provides a 48V DC power supply, which is very suitable for this system.

During connection, connecting the positive terminal of the four batteries in series to the ground wire naturally creates a -48V system voltage. This connection method is simple, direct, and reliable.

4. Personal Safety and Fault Protection

Voltage Safety: The -48V voltage value is lower than the generally accepted 60V DC safe voltage limit. Even if maintenance personnel accidentally touch the power line during operation, the probability and severity of electric shock are far lower than with 220V AC or higher DC voltages.

Fault Diagnosis: In a positively grounded system, if cable insulation is damaged or a line comes into contact with the cabinet, a short circuit will immediately occur because the cabinet is grounded (positive). This will cause the fuse to blow or the circuit breaker to trip, quickly locating the fault and preventing it from escalating.

Why -48V, and not another value?

This voltage value is the result of a technical and economic trade-off: The voltage cannot be too low: If the voltage is too low (e.g., 12V), the current will be very high when transmitting the same power (P=VI). High current leads to significant voltage drop across the cable and high energy loss (I²R), requiring thicker and more expensive wires.

The voltage cannot be too high: If the voltage is too high (e.g., 220V DC), although the current is lower and line loss is lower, the insulation requirements are higher, personal safety risks increase, and it no longer falls within the category of extra-low safety voltage.

48V is a "sweet spot": it achieves the best balance between transmission efficiency, cable cost, safety, and compatibility with the battery.