# High-Voltage Direct Current Distribution Inside the densest racks, power no longer alternates. Direct current is distributed along a rack-height busbar at several hundred volts, and the servers take it straight from the bar. The change is recent, driven entirely by density, and it quietly removes several of the conversions that a traditional alternating-current design performs between the grid and the processor. > [!note] The one-sentence version > Every conversion between alternating and direct current costs efficiency and equipment; converting once, at the rack, and distributing direct current to the servers removes most of them. ## Why it exists Semiconductors run on direct current. A conventional path converts alternating to direct current and back several times: at the uninterruptible power supply, inside each server's power supply, and again at each voltage regulator on the board. Each conversion loses a few percent and requires hardware that must be bought, cooled, and maintained. At ten kilowatts per rack the accumulated waste was tolerable. At well past a hundred kilowatts per rack, with racks drawing in the region of two hundred kilowatts and more in current rack-scale systems, it is a significant fraction of the facility's power and a significant fraction of its heat. ## Prerequisites - **Rectifier:** converts alternating current to direct current. - **Inverter:** converts direct current to alternating current. - **Busbar:** a solid conductor, typically copper, running the height or length of a rack or row, from which equipment taps power; see [[wiki/Busbar Busway|Busbar Busway]]. - **Point-of-load regulator:** the converter on the board that produces the low voltage a processor actually needs, often under one volt at very high current. - **Arc behavior:** direct current does not cross zero as alternating current does, so an arc does not self-extinguish at a current zero; interrupting direct current requires devices designed for it. - **Power shelf:** a rack-mounted assembly of rectifiers, often with integrated energy storage, feeding the rack busbar. ## How it works Medium voltage arrives at the row and is stepped down and rectified once, in a power shelf or a sidecar cabinet, to a direct-current bus at several hundred volts. The bus runs the rack. Each compute tray taps the bus and converts down in one or two stages to the voltages the accelerators and memory require. Energy storage can sit directly on the bus, which means a brief grid disturbance is ridden through by capacitors and cells on the same conductor rather than by a separate uninterruptible power system; see [[wiki/Data Center Batteries|Data Center Batteries]]. Protection uses fuses and direct-current rated breakers, and the design relies more heavily on current limiting and fast electronic disconnection than an alternating-current design does. ## What it buys and what it costs The gains are fewer conversion stages, higher end-to-end efficiency, less heat generated inside the rack, fewer discrete power supplies to fail, and more of the rack's volume available for compute and cooling. The costs are a supply base that is younger than the alternating-current one, protection engineering that cannot borrow a century of practice unchanged, electricians who must be trained for direct-current work at these voltages, and standards that are still consolidating around voltage levels and connector types. The industry's current convergence point, as of October 2026, is in the region of eight hundred volts direct current for rack distribution, carried through open hardware specifications. ## Stack position - **Upstream:** [[wiki/Medium-Voltage Distribution|medium-voltage distribution]] and the rectifier stage. - **Downstream:** [[wiki/Compute Tray|compute trays]] and the accelerators themselves. - **Function and vendor:** this is one of several valid power architectures; alternating-current distribution with in-server supplies remains correct at moderate density and is better supported by existing practice. - **Degraded case:** a dense rack fed by conventional distribution spends more of its power budget and more of its volume on conversion, which lowers the compute installed per megawatt delivered. ## Lineage and trajectory Direct-current distribution in telecommunications is a century old, at forty-eight volts, and its reliability record is excellent; the data center has now adopted the same idea at a far higher voltage because the power per rack demands it. Open rack specifications published through industry consortia have carried the design from single-vendor practice into something several manufacturers build to, which is the condition under which a supply base grows. The trajectory runs toward higher bus voltages, integrated storage on the bus, and power architectures co-designed with the accelerator rather than specified around it. ## Relationships - **fed by:** [[wiki/Medium-Voltage Distribution|Medium-Voltage Distribution]] · [[wiki/Power Transformer|Power Transformer]] - **distributed by:** [[wiki/Busbar Busway|Busbar Busway]] - **feeds:** [[wiki/Compute Tray|Compute Tray]] · [[wiki/Accelerator|Accelerator]] - **integrates:** [[wiki/Data Center Batteries|Data Center Batteries]] · [[wiki/Uninterruptible Power Supply|Uninterruptible Power Supply]] - **standardized through:** [[wiki/OCP Accelerator Module|OCP Accelerator Module]] - **source articles:** [[articles/Vertically Integrating an AI Superpower from AI Factory to Citizen|Vertically Integrating an AI Superpower from AI Factory to Citizen]] · [[articles/The Gigawatt Is the New Measure of War|The Gigawatt Is the New Measure of War]] - **collection route:** [[collections/American Infrastructure|American Infrastructure]] · [[collections/American|American Collection]] ## Evidence posture - **Established:** the loss and equipment cost of repeated alternating-to-direct conversion; direct-current arc behavior and its protection consequences; forty-eight-volt direct-current distribution as long-standing telecommunications practice; rack-scale systems drawing in the region of two hundred kilowatts and above. - **Established (datestamped):** as of October 2026, rack direct-current distribution in the region of eight hundred volts is being standardized through open hardware specifications. - **Strongly indicated:** measurable end-to-end efficiency gains from stage removal; vendor measurements agree in direction and independent facility-level data is still limited. ## Sources - [Helios Is AMD's First AI System To Rival Nvidia Vera Rubin](https://www.cnbc.com/) — CNBC, October 2026; rack power envelopes in the region of two hundred and twenty-five to two hundred and forty-five kilowatts. - Open Compute Project rack and power specifications, as published and reviewed October 2026.