Why Do Most Communication Devices Use DC 48V?

In communication infrastructure—whether it is the RRU of a 5G base station, servers in data centers, or switches in outdoor cabinets—DC 48V is almost universally adopted as the standard supply voltage. This seemingly fixed parameter is not a random choice; rather, it is the result of nearly a century of technological evolution. As the “golden standard,” 48V strikes the balance between efficiency and safety while meeting the unique requirements of communication scenarios, making it the globally recognized norm.

This article examines the historical origin, technical advantages, safety features, and industrial applications to explain why DC 48V has become the mainstream power supply for telecom equipment.

I. Historical Origin: From Telephone Networks to Modern Telecom – The “Voltage Legacy”

1. Early Telephone Networks: The “Voltage Selection Gene”

In the late 19th century, early telephone systems relied on lead-acid batteries (the dominant energy storage device). Each lead-acid cell had a nominal voltage of 2V. Engineers found that connecting 24 cells in series (2V × 24 = 48V) provided a voltage level that:

• Delivered sufficient driving power for long-distance voice transmission without distortion.

• Avoided high line loss, since low-voltage DC has much lower transmission losses in copper cables than high-voltage AC.

• Maximized battery cycle life (500–800 cycles at 48V), compared with reduced life at 60V or bulkier, more costly configurations at 24V.

Thus, 48V became embedded as the “genetic code” of telecom power supply, passed down as the industry evolved from wired telephony to wireless base stations and microwave communication.

2. Standardization and “Path Dependence”

By the mid-20th century, telecom operators like AT&T and British Telecom had adopted 48V at scale. Supporting ecosystems (rectifiers, batteries, connectors) were all designed for 48V. To avoid compatibility issues and massive redesign costs, the ITU officially included 48V DC as the preferred telecom supply standard in its 1980 guideline.
From 2G to 5G, the industry retained this voltage—not because 48V is the only possible choice, but because replacing it would require redesigning billions of devices and impose billions in added costs.

II. Technical Advantages: Meeting the “Low-Voltage DC Needs” of Telecom Equipment

1. Lower Power Consumption and Less Heat

Core components (chips at 3.3V/5V, RF modules at 12V) require DC-DC conversion. With input voltages in the 36–72V range, converters achieve peak efficiency (92–96%), making 48V the sweet spot.

• At 24V, converters drop to 85–88% efficiency due to higher currents.

• At 60V, efficiency is acceptable but requires higher-rated components, raising costs by over 20%.
  Additionally, lower current at 48V reduces I²R losses and heat, decreasing the need for fans and heatsinks, and improving reliability.

2. Avoiding AC Instability

DC avoids frequency and phase fluctuations (50/60Hz) inherent in AC, which can distort RF signals and raise bit error rates.
It also integrates seamlessly with batteries, eliminating conversion steps and efficiency losses seen with AC plus inverters.

3. Reduced Line Loss in Distributed Deployment

Telecom gear is often deployed far from power rooms. At equal power, higher voltage reduces current and therefore losses.

• At 100W, 200m cable: 48V → 7.3% loss; 24V → 29.4% loss; 220V AC → minimal loss but needs costly transformers/inverters.
  Thus, 48V balances line loss against equipment cost and complexity.

III. Safety Features: Protecting Facilities and Personnel

1. Low-Voltage Safety (SELV Compliance)

Under IEC standards, voltages below 60V are Safety Extra-Low Voltage (SELV). At 48V, even direct human contact causes harmless currents (<48mA, far below fatal 50mA). This allows safer operations without heavy protective gear, unlike 220V/380V AC.

2. Reduced Fire Risk

At higher voltages, short circuits produce strong arcs that can ignite components. At 48V, arcs are weaker and quickly cut off by fast fuses (≤10ms). In contrast, 220V AC arcs carry far more energy, creating higher fire risks.

IV. Practical Applications: A Mature “Ecosystem Loop”

1. Power Equipment Ecosystem

Suppliers like Huawei, Vertiv, and Delta provide full ranges of 48V systems:

• Rectifiers (42–58V output, ≥94% efficiency).

• Standardized batteries (lead-acid and lithium).

• Distribution units and connectors, all interoperable.

This mature ecosystem reduces procurement costs (by 15–20%) and simplifies maintenance.

2. Device-Level Adaptation

Vendors such as Ericsson, Nokia, and ZTE design equipment around 48V by default:

• Chipsets are optimized for 48V DC-DC input.

• Hardware layouts include standard 48V connectors.

• Products undergo tests across 42–58V ranges.

For example, 5G RRU units run at 48V, 300W. Switching voltage levels would require redesigns, add millions in R&D cost, and delay product launches.

Conclusion: 48V DC – The “Optimal Balance” for Telecom Power

DC 48V is the telecom industry’s best compromise between history, efficiency, safety, and ecosystem maturity.

• Historically, rooted in lead-acid batteries and reinforced by decades of practice.

• Technically, optimized for conversion efficiency, distributed deployment, and system stability.

• Safely, below SELV threshold, minimizing risks.

• Industrially, backed by a complete, cost-efficient ecosystem.

Looking forward, with 6G, satellite communications, and the widespread use of lithium batteries (3.2V × 15 = 48V), the 48V standard will not only persist but expand into edge computing and IoT, as its advantages align perfectly with the industry’s demands for stability, efficiency, safety, and cost control.