Data Center Facility - Low Voltage Direct Current Power Distribution, Version 1.1.0

Overview

The document starts from the observation that AI workloads push rack power density and load dynamics beyond traditional AC architectures. Its scope is LVDC distribution (up to 1500 VDC) between the MVAC input in the gray space and IT rack compute in the white space. MV-to-LVDC conversion is treated through an MV power supply, commonly called a solid state transformer (SST), or other components. Energy storage is included, but direct connection to the LVDC bus is excluded and a converter interface is required. MVDC, for example 2000 VDC for PV, is also out of scope. Version 1.1.0 (2 September 2026) adds chapters on the IT rack, control and operation, and EMC.

The case is made with concrete numbers. The Mt. Diablo power rack (sidecar) lets an ORv3 HPR rack move from AC power shelves of 33 kW (v1) or 72 kW (v2) to DC-supplied HPR v4 shelves of 100 kW within the same 1 OU, a 39% increase in power density per shelf. On the AC side the number of feeds is the limit: eight 100A feeds derated to 80A at 415 VAC give roughly 460 kW (no redundancy), and reuse of existing 600 VAC busway gives roughly 665 kW. Moving in-rack energy storage out of the rack frees 12-16 OU, a further 27-36% of a 44 OU rack.

The technical body follows four axes. The voltage chapters cover LV and ELV definitions, band definitions and an interoperable band proposal that treats U5 at 840 VDC as the key anchor. The polarity and earthing chapter compares unipolar and bipolar systems and TN-S against IT earthing. The protection chapter covers overcurrent, selectivity, fuses, mechanical breakers, solid-state breakers and arc hazards. Component chapters address the utility interface, AC/DC conversion, ESS, distribution and the AI rack.

The conclusion states plainly that the framework is a first step. The standardisation gap is named as the main obstacle: there is no system-level topology guidance, a validated DC arc-flash methodology is urgently needed, and until formal installation codes (the 2029 NEC) are finished the paper recommends Outlines of Investigation, hazard-based risk assessment and hardware-in-the-loop simulation. The voltage band proposals are drafts and will be revisited after the OCP SST source specification.

Key points

1. Scope is LVDC (up to 1500 VDC) from MVAC input to the IT rack; MVDC and direct connection of ESS to the LVDC bus are out of scope.
2. A DC power rack with HPR v4 100 kW shelves gives 39% more density in the same 1 OU than 33 kW (v1) and 72 kW (v2) AC shelves.
3. AC rack ceiling: eight 100A feeds derated to 80A give about 460 kW at 415 VAC (no redundancy), about 665 kW with 600 VAC busway. The 50 VDC vertical bus is a separate in-rack bottleneck; an 800 VDC vertical bus approaches the 1+ MW roofline.
4. Moving backup energy storage out of the rack frees 12-16 OU, 27-36% more space in a 44 OU rack.
5. Low voltage is up to 1000 VAC or 1500 VDC; for interoperability U5 = 840 VDC is proposed as the highest designed protection voltage, and sources must not exceed it.
6. Likely combinations include 350/700 V bipolar TN-S with (partially) distributed M (400/800 V), the system in the Mt. Diablo specification, which has lower voltage to earth than unipolar 700 V.
7. In ungrounded IT systems total Y-capacitance must be limited, so IT earthing does not work for large systems; TN-S with selective branch RCDs is the route to scale, with System Referencing Devices (SRDs) to avoid corrosion from multiple earth references.
8. Field evidence: Schaltbau's NExT factory (since 2023, 2-wire DC up to 750 V band), a BMW body cell using 8.8% less energy after about two years, and ABB's 2012 DC data centre.
9. DC arc-flash rules are named as the current bottleneck for supply chain and installation; interim guidance is recommended until the 2029 NEC.

Using it in design

• Choose the voltage class with LV limited to 1500 VDC; check that sources stay below it in steady state (for example 750 V per pole) and that device voltage windows fit; 800 V devices with only a +/-5% range cannot operate below 750 V and are unusable there.
• Choose polarity and earthing together: 350/700 V bipolar TN-S is consistent with the Mt. Diablo sidecar and has lower voltage to earth; unipolar 700/800 V needs larger clearances and creepage.
• If IT earthing is considered, calculate total Y-capacitance and verify the scale limit; for large systems evaluate TN-S with branch-level RCDs and SRDs.
• In the protection study address selectivity, fault-current limiting on DC lines, solid-state breaker options and a separate DC arc risk analysis; where no installation code applies, rely on Outlines of Investigation and HIL simulation.
• In rack architecture plan the power-rack to IT-rack interface (LVDC input conversion shelf, hot-swap control, precharge) and rack- or distribution-level energy storage for power oscillation.
• At the utility interface treat voltage and frequency ride-through, ramp management and oscillation limits separately from LVDC needs; DC undervoltage ride-through with storage alone does not keep drawing power for the grid.

Who should read it

Electrical architects, protection and earthing engineers, equipment makers and authorities having jurisdiction evaluating DC distribution for high-density AI facilities.

Document contents

1. Introduction
2. Compliance with Open Compute Project Tenets
3. Background Context
4. Document Scope
5. System Architecture
6. From MV to LV - high level stages
7. Redundancy Levels
8. Power distribution redundancy schemes for DC data centers
9. Verified Benefits of DC installations
10. Voltage Levels and Power Quality
11. Interoperable Voltage Band Proposal
12. Power Quality and Grid Interaction
13. Polarities & System Earthing
14. Protection and Safety
15. Protection against overcurrent
16. Protection against electric shock
17. Protection against arc-flash
18. System Main Components
19. Interface with Rack & Power
20. System Operation, Control and Monitoring
21. Electromagnetic Compatibility (EMC)
22. Codes and Standards
23. The path forward - Key Takeaways for Stakeholders
24. Conclusion

Related standards

• IEC 60038 (AMD for LVDC)
• IEC TR 63282
• NFPA 70 (NEC)
• UL 9540 / 9540A
• OCP ORV3 HVDC-LVDC 100 kW Power Shelf

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Publication details

Authors

Open Compute Project Foundation

Publisher

Open Compute Project Foundation

Year

2026

Document number

v1.1.0

Document language

English

Source type

Industry body

Access

Open licence — downloadable

Licence

CC BY-SA 4.0 — share with attribution under the same licence

Licence evidence

www.opencompute.org

Citation