Mt. Diablo Disaggregated Power Rack Specification 1.0.0 (effective October 8, 2026)

Overview

The specification starts from the observation that rack power growing from 33 kW to hundreds of kW, larger accelerators and growing rack/POD size create significant challenges in interconnect density, power delivery and system integration. Its answer is the disaggregated power rack (sidecar): the power rack scales from 800 kW to 1 MW+ (power racks can be paralleled) while the IT rack stays the same. Three companies' dimensions are given separately: Microsoft 2329 x 600 x 1200 mm, Meta 2329 x 600 x 1219 mm and Google 2329 (up to 2410 mm) x 711 x 1219.2 mm, with a target load capacity of 6000 lb. Tolerances are left to a future revision.

On the AC side the rack accepts a single or dual N+N redundant 3-phase input: WYE or delta 480/415/400 V (+/-10%), 50/60 Hz (+/-3 Hz). For power quality, PF must exceed 0.95 below 20% load and 0.99 at 20% load or more, and current THD must be under 5% at 30% load or more. PSUs must ride through per ITIC and IEC 61000-4-34, and minimum holdup without storage is up to 20 ms at 100% load. Energy storage options are a BBU (45-90 s at 100% load) or a capacitor bank (CBU).

The DC output is +400 and -400 V to common (410 V no load, 400 V full load, +/-0.5% regulation), 800 VDC differential, with 10 V built-in droop and +/-3% transient. Average rack power 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; for short peaks the rack must support 175-180% of TDP for load steps under 2 ms, and the BBU must not trigger during peak loading. End-to-end efficiency at 480 VAC is above 95% at 20% load, above 98% at 50% and above 97% at 100%.

Building blocks are the AC/DC PDU (up to 16 x 200 A or 24 x 100 A cords), AC/DC PSU shelves up to 2OU (up to 30 kW per PSU at 480 VAC), a vertical 3-conductor busbar designed for 1.1 MW average load, and DC output modules at 50 kW or 100 kW per cable. Midpoint grounding options (high resistance or solid) and a ground fault detector are defined. The safety section covers SCCR (10-40 kA), leakage current (3.5 mA AC, 10 mA DC), UL 9540A fire propagation testing and EMC Class A. Environmental conditions are -5 to 35 C required (45 C preferred) up to 3050 m without derating; dimensional tolerances are left to a future revision and connector part numbers are preliminary.

Key points

1. A power rack scales from 800 kW to 1 MW+ (can be paralleled) while the IT rack stays the same; rack power has grown from 33 kW to hundreds of kW.
2. Dimensions (H x W x D, mm): Microsoft 2329 x 600 x 1200; Meta 2329 x 600 x 1219; Google 2329 (up to 2410) x 711 x 1219.2; target load capacity 6000 lb.
3. AC input: 3-phase WYE 480/415/400 V (+/-10%) or delta, single feed or dual N+N; PF above 0.99 at 20% load or more; current THD under 5% at 30% load or more.
4. PSUs ride through per ITIC and IEC 61000-4-34; minimum holdup without storage up to 20 ms at 100% load.
5. BBU option gives 45-90 s backup at 100% load; capacitor-bank (CBU) storage is also supported.
6. DC output +400/-400 V to common (410 V no load / 400 V full load), 800 V differential, +/-0.5% regulation, 10 V droop, +/-3% transient.
7. Average rack power 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 BBU must not trigger during peak (pulse) loading.
8. End-to-end efficiency at 480 VAC: >95% at 20% load, >98% at 50%, >97% at 100%.
9. AC PDU accepts up to 16 x 200 A or 24 x 100 A cords; DC output cables range from 63 A/50 kW to 125 A/100 kW each.
10. Operating environment -5 to 35 C (required), 45 C (preferred); 10-90% RH; altitude up to 3050 m without derating; fully air-cooled, front-to-back airflow.

Using it in design

• Add a sidecar power-rack block (600/711 mm wide, about 1200 mm deep, 6000 lb) to AI row layouts with its own floor-load and clearance checks, and model +/-400 VDC distribution from it to IT racks.
• In the power chain design size upstream AC feeds for up to 1.1 MW per power rack at 480 V (718 kW at 400 V).
• Apply the PF and THD limits (PF >0.99, THD <5%) in harmonic studies.
• Treat 45-90 s BBU autonomy as the ride-through that generator start and transfer must fit within; compare the 20 ms no-storage holdup with UPS and transfer-switch transitions.
• Add the midpoint grounding choice (high resistance or solid), the ground fault detector and per-cable residual current detection to the protection study.
• Check power rack placement against -5 to 35 C operation, front-to-back airflow and containment rules that prevent hot air recirculation.

Who should read it

Electrical engineers designing DC power racks for AI rows, power rack and PSU manufacturers and hyperscaler hardware teams.

Document contents

1. License
2. Open Web Foundation (OWF) CLA
3. Acknowledgements
4. Compliance with OCP Tenets
5. Scope
6. Rack Physical Dimensions
7. Mechanical Features
8. Voltage Distributions
9. Rack AC Power Requirements
10. AC Input Voltage
11. AC Input PF and THD
12. AC Loss (Holdup and ride-through)
13. Energy Storage Solutions
14. BBU Option
15. Capacitor Bank Option CBU
16. Rack DC Power Requirements
17. DC Output Voltage for Nominal +/-400VDC
18. DC Output Power for Nominal +/-400VDC
19. DC Output - Dynamic loading
20. End to End Output Power Conversion Efficiency
21. Multi Rack Parallel Option
22. Power Rack Building Blocks
23. AC & DC PDU
24. AC/DC PSU Shelf
25. DC Output Interconnect Cables
26. AC Input Interconnect Cables
27. Management, telemetry and communication interface with the sidecar
28. Operating Environmental Conditions
29. Regulatory and Compliance Requirements
30. Safety Requirements
31. Electromagnetic Compatibility (EMC) Requirements
32. Environmental, Eco-Design, and Sustainability Requirements

Related standards

• OCP Diablo 400 Rack and Power Base Specification
• ITIC curve
• IEC 61000-4-34
• OCP DCF LVDC Power Distribution white paper

Read the document

Publication details

Authors

Microsoft, Meta, Google

Publisher

Open Compute Project Foundation

Year

2026

Document number

v1.0.0

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