In modern communication networks—from 4G and 5G to future 6G—mobile base stations form the backbone of wireless connectivity. Behind this infrastructure lies a seemingly minor yet critical design choice: almost all telecom base stations worldwide operate on –48V DC power.

For many outside the industry, this raises obvious questions:

Why –48V instead of +48V?

Why not 220V AC, or more common voltages like 12V or 24V?

The answer lies in a combination of engineering logic, safety considerations, and over a century of industry evolution.

1. Where Did –48V Come From?

Historical Origins and Standardization

The –48V DC system originated in early telephone exchange networks in the early 20th century.

At the time, engineers needed a voltage level that could:

Support long-distance power transmission with acceptable voltage drop

Reliably operate electromechanical relays and telephone circuits

Enable ringing signals without excessive complexity

Around 50V DC proved to be the optimal solution. Over time, 48V became the standardized nominal voltage.

To further enhance safety and interference resistance, engineers adopted a negative-ground system, where:

The negative pole is grounded

The positive pole operates at –48V relative to ground

This design laid the foundation for today’s –48V DC power systems.

International standards such as ITU, YD/T, and NEBS formally define –48V DC as the primary operating power for telecom equipment—a standard that has remained unchanged for decades.

2. Why “Negative” Voltage?

The Engineering Logic Behind –48V

Contrary to common misconceptions, “–48V” does not imply reversed current flow or reduced power. Voltage is always a relative reference.

The choice of negative grounding offers several critical advantages.

2.1 Reduced Electrochemical Corrosion (Cathodic Protection)

This is the most important physical reason for adopting negative voltage.

When metal conductors are exposed to humid environments, conductors at a higher potential than ground are more susceptible to oxidation and corrosion. In a –48V system:

Signal and power conductors remain at a lower potential relative to ground

The system naturally provides a cathodic protection effect

This significantly reduces corrosion of:

Outdoor cables

Connectors

PCB traces

Especially in hot and humid environments, this design greatly extends equipment lifespan.

Similar to how sacrificial anodes protect ship hulls, –48V systems use controlled potential to mitigate corrosion.

2.2 Improved Safety and System Stability

Negative grounding also enhances operational safety:

Equipment enclosures remain at ground potential, reducing electric shock risk

Fault currents and lightning-induced surges are safely discharged

A unified ground reference minimizes common-mode interference in remote radio units (RRUs)

3. Why 48V?

Engineering Trade-Offs Behind the Voltage Level

Why not 12V, 24V, 60V, or even higher DC voltages?

3.1 Within the Safe Voltage Range

According to IEC standards, SELV (Safety Extra-Low Voltage) is defined as ≤60V DC.

At 48V, telecom systems remain within this safe range, making them ideal for:

Unmanned base stations

Outdoor and remote deployments

Maintenance without complex insulation requirements

3.2 Optimized Power Transmission Efficiency

Lower voltages require higher current for the same power output, increasing cable losses (I²R).

Example at 240W:

12V → 20A

48V → 5A

This results in:

1/16 of the line loss

Reduced heat generation

Lower cable cost and improved reliability

3.3 Natural Compatibility with Battery Systems

48V systems align perfectly with traditional telecom backup batteries:

24 × 2V lead-acid cells = 48V

Easy integration with lithium battery systems

Simplified DC/DC conversion and modular UPS design

4. Typical –48V DC Power Architecture in Base Stations

A standard telecom power system includes:

AC Distribution Unit – connects to utility power

Rectifier Modules – convert AC to –48V DC (often N+1 redundant)

DC Distribution Unit – supplies power to baseband, transmission, and auxiliary loads

Battery Bank – provides seamless backup during outages

Power Monitoring System (PSMS) – enables real-time monitoring and remote management

Key system characteristics:

High availability through redundancy

Uninterrupted operation with battery backup

Intelligent management with alarms and energy optimization

5. Why Not Other Power Methods?

The –48V DC system remains the best balance between safety, efficiency, reliability, and ecosystem maturity.

6. Will –48V Be Replaced in the Future?

While technologies such as HVDC, solar integration, and lithium-based power cabinets continue to evolve, –48V DC remains irreplaceable in the near term due to:

Massive global installed base

Fully standardized supply chains

Seamless compatibility with next-generation hybrid power systems

The future is more likely –48V + intelligence + renewable integration, rather than complete replacement.

Conclusion

The choice of –48V DC power is far more than a historical convention—it represents a century of engineering optimization balancing safety, reliability, efficiency, and long-term sustainability.

From early telephone exchanges to today’s 5G and beyond, –48V DC continues to quietly power the world’s communication networks.

It may not be visible to end users—but it remains one of the true unsung heroes of global connectivity.