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  "title": "Rack power shelf and DC busbar",
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  "description": "Converts incoming power and distributes controlled DC supply throughout the rack.",
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  "revisionDate": "2026-10-07",
  "author": null,
  "topic": "Electrical infrastructure",
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      "title": "Explore in Atlas",
      "url": "https://semiaifoundry.com/ai-atlas/#power-shelf"
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    {
      "title": "NVIDIA — DGX GB Rack Scale Systems Hardware Guide",
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    {
      "title": "Power supply and power shelf",
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      "title": "Integrated accelerator rack: GB200 NVL72 example",
      "url": "https://semiaifoundry.com/learn/atlas/rack/"
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    {
      "title": "GB200 compute tray",
      "url": "https://semiaifoundry.com/learn/atlas/compute-tray/"
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      "title": "Uninterruptible power supply and backup chain",
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  "content": "Electrical infrastructure · Atlas v1.3.0\n\n# Rack power shelf and DC busbar\n\nConverts incoming power and distributes controlled DC supply throughout the rack.\n\n[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#power-shelf)Rack-scale power modules and busbar; conceptual circuit path\n\nLearning objectiveTrack conversion power and resistive distribution loss as distinct terms.\n\n## The mechanism\n\nThe power shelf links facility electricity to the rack's internal power distribution. In the documented DGX GB example, shelves convert AC input into a nominal fifty-to-fifty-one-volt DC output delivered through a busbar. Downstream regulation then creates the voltages required by electronics. Multiple shelves provide capacity and redundancy, so adding their nameplate ratings does not reveal the actual workload power. The atlas exposes the conversion modules and their shared conductor, while keeping the electrical path separate from data cables and coolant hoses. A high-performance rack can draw large and changing power as its workload changes. Reliable supply and system-level control are prerequisites for the switches and memory deeper in the atlas to operate.\n\n1.  Receive facility power through the rack power infrastructure.\n2.  Convert it to the specified DC busbar supply.\n3.  Distribute DC to the trays, where downstream regulators supply individual components.\n\n## Science and assumptions\n\n### Power conversion and conductor loss\n\n$$\nP_{DC}=\\eta P_{AC},\\qquad P_{\\mathrm{wire}}=I^2R\n$$\n\nDelivered DC power is conversion efficiency times real AC input power. Conductor heating is current squared times resistance.\n\nSymbols and units\n\nP\\_DC\n\nDelivered direct-current power\n\nW\n\nη\n\nConversion efficiency\n\nfraction\n\nP\\_AC\n\nInput real alternating-current power\n\nW\n\nP\\_wire\n\nResistive conductor heating\n\nW\n\nI\n\nConductor current (DC or appropriate RMS)\n\nA\n\nR\n\nConductor resistance\n\nΩ\n\nEfficiency η determines conversion loss. At a given delivered power, distribution voltage influences current, while resistive heating rises with current squared.\n\nAssumptions Steady power bookkeeping and resistive conductor model; AC power factor, transient response, protection, and equipment limits are separate considerations.\n\n## Engineering example\n\nSynthetic shelf: 100 kW AC input at 97% conversion efficiency yields 97 kW DC and 3 kW conversion loss. A separate conductor carrying 1,000 A with resistance 0.1 mΩ dissipates I²R = 100 W. That conductor loss must not be counted as useful downstream power.\n\n## Distinctions and tradeoffs\n\nThe rack busbar voltage is not the transistor supply voltage, and installed PSU ratings are not measured workload consumption.\n\nRedundancy improves service continuity. Conversion losses and capacity margins still consume infrastructure resources.\n\nAI operations ultimately depend on electrical energy. Power distribution determines how much hardware can operate reliably at once.\n\n## Specifications and interfaces\n\nDGX GB example DC output\n\nNominal 50–51 V\n\nRack busbar output, not GPU core voltage.\n\nReference rack consumption\n\n≈120 kW\n\nHardware-guide example; actual draw varies by configuration and workload.\n\nShelf organization\n\nMultiple redundant shelves\n\nNameplate capacity must not be confused with consumption.\n\n### Interfaces\n\nFacility electrical feed Input\n\nAC power\n\nRack busbar Output\n\nDistributed DC power for downstream conversion\n\n## Check your understanding\n\n### What does the nominal 50–51 V figure describe here?\n\n1.  The voltage across every transistor gate\n2.  The optical-fiber signal voltage\n3.  The documented rack DC busbar output\n\nAnswer and reasoning\n\nThe documented rack DC busbar output\n\nFurther regulation inside the system produces component-level supply voltages.\n\n## Evidence and scope\n\nThe example uses steady real-power accounting and a separate resistive segment. Values are synthetic; current limits, protection, voltage drop, AC power factor and transients require additional engineering checks.\n\nNo current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.\n\n## Sources\n\n-   [NVIDIA — DGX GB Rack Scale Systems Hardware Guide](https://docs.nvidia.com/dgx/dgxgb200-user-guide/hardware.html)\n\n[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/power-shelf-06effe71ff9121fd.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)\n\n## Continue exploring\n\n### Foundations\n\n-   [Power supply and power shelf](https://semiaifoundry.com/learn/atlas/power-supply/)\n\n### Related lessons\n\n-   [Integrated accelerator rack: GB200 NVL72 example](https://semiaifoundry.com/learn/atlas/rack/)\n-   [GB200 compute tray](https://semiaifoundry.com/learn/atlas/compute-tray/)\n-   [Uninterruptible power supply and backup chain](https://semiaifoundry.com/learn/atlas/ups/)\n-   [Facility cooling and final heat rejection](https://semiaifoundry.com/learn/atlas/cooling-plant/)"
}