Diablo 400 Project: Rack and Power, Base Specification Version 0.7.0 (effective March 1, 2026)

Overview

The specification responds to rack power rising from 33 kW to hundreds of kW, with AI accelerators and larger pods straining interconnect density and power delivery. A disaggregated power rack, called a sidecar, scales from 800 kW to 1 MW or more, with the option to parallelize racks, while the IT rack stays the same. The OCP tenets text argues that higher voltage reduces I2R losses, that the power rack can serve several IT rack generations in place, and that the architecture can borrow from electric vehicle DC technology at +/-400 VDC or 800 VDC. The base follows Open Rack. Dimensions are listed for each company: height 2,329 mm for all three, width 600 or 711 mm, and depth 1,200 to 1,219.2 mm, with a 6,000 lb target load.

On the AC side, the rack takes a 3-phase input, single or dual for N+N, at nominal 480, 415 or 400 Vrms, plus or minus 10%, 50/60 Hz plus or minus 3 Hz. Power factor must exceed 0.95 below 20% load and 0.99 at or above 20%, and current THD must be under 15% at 5-15% load, under 10% at 15-30% and under 5% at 30% and above. PSU hold-up without energy storage is at least 20 ms at 100% load. Energy storage can be a battery backup unit, supporting 45 to 90 seconds of hold-up at 100% load, or a capacitor bank. Racks deliver 800 kW to 1.1 MW at 480 VAC, up to 1.1 MW at 415 VAC and up to 718 kW at 400 VAC.

The DC output is nominally 410 VDC at no load and 400 VDC at full load for each of the + and - rails against common, regulated to plus or minus 0.5%. Requirements include steps of 175% of TDP in under 2 ms and 150% in under 50 ms without triggering the BBU, and dynamic steps up to 140% at 10 kHz with plus or minus 3% deviation. End-to-end efficiency from AC PDU input to DC PDU output must exceed 95% at 20% load, 97-98% at 50% load and 96.5-97% at full load. Building blocks include a PDU for up to 12 x 200 A cords, DC output modules to 400 kW, 2OU PSU shelves with 25-30 kW modules and a busbar for up to 1.1 MW.

Safety and grounding receive specific treatment. Mid-point grounding may be high-resistance or solid, with a ground fault detector on each output (required for high-resistance), output cables rated 50 kW (63 A) to 100 kW (125 A) with latching, short-pin connectors, and output ports de-energizing when unplugged. Cable voltage drop budget is 0.1% at 5 m. The rack is air-cooled, with ambient of -5 to 45 °C preferred (-5 to 35 °C required), 10-90% RH non-condensing, altitude up to 3,050 m and thermal margin of at least 4% or 3 °C. Short-circuit rating of 10 to 40 kA, management by Redfish or proprietary interfaces and EMC and eco-design requirements follow. Several sizes and tolerances are marked for later revision.

Key points

1. The sidecar scales from 800 kW to 1 MW or more, with an option to parallelize racks; rack average DC load is 800 kW to 1.1 MW at 480 VAC, up to 1.1 MW at 415 VAC and up to 718 kW at 400 VAC.
2. AC input is 3-phase at 480, 415 or 400 Vrms +/-10%, single feed or dual N+N, 50/60 Hz +/-3 Hz.
3. Power factor is above 0.95 below 20% load and above 0.99 at 20% load and over; THD is under 15%, 10% and 5% in the three load bands.
4. PSU hold-up without energy storage is at least 20 ms at 100% load; battery backup time with BBU is 45 to 90 seconds at 100% load.
5. DC output is 410 VDC at no load and 400 VDC at full load for +400 and -400 against common, +/-0.5%.
6. Required step responses include 175% of TDP in under 2 ms and 150% in under 50 ms, with BBU backup not triggered; dynamic load steps of 50%, 90% and 140% at 1 A/us up to 10 kHz with +/-3% deviation.
7. End-to-end efficiency minimums: above 95% at 20% load, 97-98% at 50% load, 96.5-97% at 100% load.
8. DC output cables carry 50 kW (63 A) to 100 kW (125 A) with a 0.1% voltage drop budget at 5 m; connectors latch with a switch so the cable cannot be removed under load.
9. The rack is fully air-cooled: ambient -5 to 45 °C preferred (-5 to 35 °C required), 10-90% RH, altitude up to 3,050 m, thermal margin of at least 4% or 3 °C.
10. This is a v0.7.0 pre-release: tolerances, PSU sizes and some figures are explicitly to be defined in later revisions.

Using it in design

• Check that the facility's AC feed (480, 415 or 400 V, single or dual) and the rack power range match the planned IT block, including up to 1.1 MW per sidecar and the parallel option.
• Specify power quality at the input as given (PF above 0.99 from 20% load, THD under 5% above 30% load), and verify upstream equipment tolerates the pulse and step-load profiles.
• Size the ride-through approach, either PSU hold-up of 20 ms or a BBU or capacitor bank covering 45 to 90 seconds, against the generator start time.
• Select the grounding scheme (high-resistance or solid mid-point) early, because it determines ground fault detection and safety design.
• Budget the output cable length and cross-section against the 0.1% voltage drop at 5 m and plan 50 or 100 kW cables per output.
• Plan cooling for a front-to-back air-cooled rack with its stated ambient, humidity and altitude limits, and leave the open dimensions flagged for later revisions.

Who should read it

Electrical designers, rack and power-system vendors and AI data center planners evaluating 400 or 800 VDC disaggregated power racks.

Document contents

1. License
2. Compliance with OCP Tenets
3. Scope
4. Rack Physical Dimensions
5. Voltage Distributions
6. Rack AC Power Requirements
7. Energy Storage Solutions
8. Rack DC Power Requirements
9. DC Output - Dynamic Loading
10. End to End Output Power Conversion Efficiency
11. Multi Rack Parallel Option
12. Power Rack Building Blocks
13. AC & DC PDU
14. +/-400VDC PE Grounding
15. AC/DC PSU Shelf
16. +/-400VDC Distribution Busbar
17. +/-400VDC to IT Rack Distribution Cable
18. Management, Telemetry and Communication Interface with the Sidecar
19. Operating Environmental Conditions
20. Regulatory and Compliance Requirements
21. Appendix A: High Resistance Grounding and Solid Grounding
22. Appendix C: DC Output Interconnect Options
23. Appendix D: AC Input Interconnect Options

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Publication details

Authors

Microsoft; Meta; Google

Publisher

Open Compute Project Foundation

Year

2026

Document language

English

Source type

Industry body

Access

Open licence — downloadable

Licence

OWFa 0.9 — Open Compute open specification licence; redistribution permitted

Licence evidence

www.opencompute.org

Citation