Open Rack V3 Power Shelf Specification, Rev 1.0 (document dated 29 April 2025)

Overview

The Open Rack power architecture uses a centralised, scalable power shelf that feeds payloads over a common busbar. The shelf houses several rectifiers with at least N+1 redundancy, and one or more shelves are used depending on rack power. The document defines two options: option 1, six 3 kW PSUs with dual cords (2x 20 A NEC breakers upstream), and option 2, six 3 kW PSUs with a single cord (32 A IEC breaker). Both give 15 kW with N+1 and connect directly to facility tap-boxes with no intermediate PDU. The revision history runs from 0.5 in 2020 to version 1.0 in 2022.

AC input is 200-277 V nominal phase-to-return, plus or minus 10%; the module must survive continuous exposure to 305 Vac RMS. Input is through a pluggable 7-pin connector configurable as star, delta or single phase, rated 32 A and angled outward so cables run along the rack sides. Facility protection is 2x 20 A NEC breakers for the dual-feed 1U shelf and a 32 A IEC breaker for the single-feed shelf, with 25 kA available short-circuit current. AC earth connects to the chassis. DC output is a narrow-range 48 V system with ripple and noise below 500 mV peak-to-peak in a 20 MHz bandwidth along the busbar regardless of load distribution; the 48 V return must not be grounded to the frame.

Mechanically, the 1 OU shelf is 537 mm wide, 46 mm high and 788.7 mm deep. It front-mounts on OU-pitch rails in the ORv3 rack; the front latch and bumper serve separate functions and must not be one part, and the latch must withstand the 16 G shock of loaded-rack shipping tests. The six rectifiers and the monitoring module (PMI) are toollessly accessible from the front, rectifiers are hot-swappable with the rack energised, and the six slot positions are fixed. Sheet metal is hot-dip zinc-coated steel of 1.0-1.2 mm; aluminium enclosures and electro-zinc plating are not allowed. Configurations with fewer than six PSUs need a slot blank to channel airflow.

On thermal matters, component margin must be at least 7% or 5 C up to 30 C inlet and 3050 m altitude, and at least 4% or 3 C above 30 C inlet (the larger value is targeted); exhaust from upstream components should not exceed 70 C. A rear-panel back-pressure of 0.2 in of water or less at 100 cfm is targeted at sea level, and accessible surfaces should stay at or below 70 C. Environment: operating -5 to +45 C, 10-90% RH non-condensing, no derating up to 3050 m, ANSI/ISA 71.04 G1 gaseous contamination and an acoustic target of 85 dBA. Vibration and shock follow EN 60068-2-6 and 60068-2-27 and package tests follow ISTA 3E; storage is -40 to +70 C.

The reliability and quality chapter sets IPC-9592B derating, DFMEA, reliability prediction, zinc-whisker controls, 100% production hi-pot and ground continuity testing, a Cpk of at least 1.33 and incoming rejection below 0.1%. The compliance chapter lists UL, IEC and EN 62368-1 safety standards, EMC requirements (including EN61000-4-11 voltage dips), RoHS, REACH, halogen-free (IEC 61249-2-21), WEEE and an EPA 40 CFR751 declaration. The document dates from 2022; newer high-power ORv3 shelves (for example the 33 kW HPR) are outside its scope.

Key points

1. The shelf holds six 3 kW rectifiers, delivers 15 kW with at least N+1 redundancy and connects directly to facility tap-boxes without an intermediate PDU.
2. Two options exist: dual cord (2x 20 A NEC breakers) and single cord (32 A IEC breaker).
3. AC input is 200-277 V nominal phase-to-return, plus or minus 10%, 50/60 Hz; the module must survive continuous 305 Vac; star, delta or single phase is configurable.
4. Facility protection is 2x 20 A NEC for dual-feed or 32 A IEC for single-feed, with 25 kA available short-circuit current.
5. DC output is a narrow-range 48 V system; ripple and noise must be below 500 mV peak-to-peak at 20 MHz and the 48 V return must not be bonded to the shelf frame.
6. The 1 OU shelf measures 537 mm W x 46 mm H x 788.7 mm D.
7. Thermal margin: at least 7% or 5 C up to 30 C inlet and 3050 m; at least 4% or 3 C above 30 C inlet; upstream exhaust at most 70 C.
8. Environment: operating -5 to +45 C, 10-90% RH non-condensing, no derating to 3050 m, G1 gaseous contamination, acoustic target at most 85 dBA.
9. Rear panel back-pressure target is 0.2 in water or less at 100 cfm; accessible surfaces at most 70 C.
10. Production requires 100% hi-pot and ground continuity testing, Cpk of at least 1.33 and incoming rejection below 0.1%.

Using it in design

• When choosing the feeding branch circuit, size option 1 for two independent 20 A NEC circuits or option 2 for a 32 A IEC circuit, check the 25 kA available short-circuit current at the outlet, and note there is no PDU in between.
• Verify that the 200-277 V phase-to-return window (plus or minus 10%) and the 32 A connector rating match the facility voltage and tap-box, and settle star, delta or single-phase wiring together with hall distribution.
• Convert the rack power budget into a number of shelves using 15 kW N+1 output per shelf, and put the ripple limit with its measurement method (20 MHz, 0.1 uF capacitor) into acceptance testing of the 48 V busbar.
• Compare hall inlet temperature, altitude and gaseous contamination design with the shelf envelope of -5 to +45 C, 3050 m and G1, and check rear airflow exit and pressure drop against the 0.2 in water target.
• Require a slot blank where fewer than six rectifiers are installed, and read the document together with the ORv3 base frame specification.

Who should read it

Power electronics engineers designing ORv3 power shelves and rectifiers, and data centre engineers designing electrical distribution for ORv3 racks.

Document contents

1. Revision History
2. Scope
3. Overview
4. Power shelf options
5. Electrical requirements
6. AC Electrical requirements (Facility Protection)
7. DC Electrical requirements
8. Rectifier physical addressing
9. Monitoring & Control Interface
10. Mechanical Requirements
11. Power Shelf Assembly Dimensions
12. ORV3 Rack Mounting Feature
13. Connectors (AC input, DC output, power supply, PMI)
14. Front Access, Construction, Materials and Fasteners
15. Labeling & Markings, PSU Slot Blank, Mechanical Drawings
16. Thermal Requirements
17. Environment/test requirements (vibration, shock, package tests)
18. Reliability and Quality
19. Compliance requirements (safety, EMC, environmental, documentation)

Read the document

Publication details

Authors

Hamid Keyhani; Dmitriy Shapiro; John Fernandes; Ben Kim; Tiffany Jin; Rommel Mercado

Publisher

Open Compute Project Foundation

Year

2022

Document language

English

Source type

Industry body

Access

Open licence — downloadable

Licence

OWFa 1.0 — Open Compute open specification licence; redistribution permitted

Licence evidence

www.opencompute.org

Citation