Why Telecom Base Stations Still Run on –48V DC Power

Telecom base stations across the world, from 4G sites to 5G macro towers, almost universally rely on a –48V DC power system. The negative sign does not mean reversed current; it means the positive terminal is bonded to earth ground, so the active conductor sits at roughly –48V relative to ground. The standard is not a modern invention but a holdover from early 20th-century telephone exchanges that proved hard to retire. 

Engineers settled on 48V as a compromise. Below 60V DC, the circuit counts as Safety Extra-Low Voltage under IEC rules, keeping technician shock risk low. At 48V, delivering the same wattage needs far less current than 12V or 24V, cutting I²R cable loss and allowing thinner copper runs across long feeder cables.

The negative polarity exists mainly to fight corrosion. Early outdoor copper cabling, soaked in damp soil, formed electrochemical cells that ate away the positive conductor. By grounding the positive side, the wire becomes the cathode and gains cathodic protection, while the large ground rod takes the tiny sacrificial loss. This trick quietly extended the life of buried telecom plants for decades.

Battery math sealed the deal: 24 lead-acid cells at 2V each make 48V, so backup banks slot straight onto the DC bus with no extra conversion. Standards bodies like ITU and NEBS froze –48V as the telecom norm, and today’s rectifiers, PDUs, and lithium backups all speak the same voltage dialect.

As 5G radios draw more power, some operators nudge float voltage to –54V or –57V, but the –48V spine stays put—proof that a century-old compromise still carries the network.