{"id":"power-shelf","level":"rack","name":"Rack power shelf and DC busbar","shortName":"Power shelf","role":"Converts incoming power and distributes controlled DC supply throughout the rack.","description":"The 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.","specs":[{"label":"DGX GB example DC output","value":"Nominal 50–51 V","context":"Rack busbar output, not GPU core voltage."},{"label":"Reference rack consumption","value":"≈120 kW","context":"Hardware-guide example; actual draw varies by configuration and workload."},{"label":"Shelf organization","value":"Multiple redundant shelves","context":"Nameplate capacity must not be confused with consumption."}],"interfaces":[{"name":"Facility electrical feed","direction":"in","signal":"AC power"},{"name":"Rack busbar","direction":"out","signal":"Distributed DC power for downstream conversion"}],"tradeoff":"Redundancy improves service continuity. Conversion losses and capacity margins still consume infrastructure resources.","whyAI":"AI operations ultimately depend on electrical energy. Power distribution determines how much hardware can operate reliably at once.","related":["rack","compute-tray","ups","cooling-plant","power-supply"],"sources":[{"title":"NVIDIA — DGX GB Rack Scale Systems Hardware Guide","url":"https://docs.nvidia.com/dgx/dgxgb200-user-guide/hardware.html"}],"scale":"Rack-scale power modules and busbar; conceptual circuit path","kind":"power-shelf","mechanism":["Receive facility power through the rack power infrastructure.","Convert it to the specified DC busbar supply.","Distribute DC to the trays, where downstream regulators supply individual components."],"misconception":"The rack busbar voltage is not the transistor supply voltage, and installed PSU ratings are not measured workload consumption.","check":{"question":"What does the nominal 50–51 V figure describe here?","options":["The voltage across every transistor gate","The optical-fiber signal voltage","The documented rack DC busbar output"],"answer":2,"explanation":"Further regulation inside the system produces component-level supply voltages."},"branch":"Electrical infrastructure","subbranch":"Rack conversion","science":[{"title":"Power conversion and conductor loss","equation":"P_DC = η P_AC; P_wire = I²R","explanation":"Efficiency η determines conversion loss. At a given delivered power, distribution voltage influences current, while resistive heating rises with current squared.","assumptions":"Steady power bookkeeping and resistive conductor model; AC power factor, transient response, protection, and equipment limits are separate considerations."}],"history":[],"prerequisites":["power-supply"],"learningObjective":"Track conversion power and resistive distribution loss as distinct terms.","engineeringExample":"Synthetic 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.","evidenceNotes":"The 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.","labId":"library","scope":"No current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions.","investigationId":"manufacturing","labScope":"No current calculator directly models this lesson’s main mechanism. Use the library for related bounds while retaining their stated omissions."}