Beyond ORv3 HPR Busbars: Enabling Next Gen AI Rack Power Levels with Liquid Cooling (OCP EMEA Summit 2025)

Overview

This document is the slide deck of an engineering talk by TE Connectivity and Meta, presented at the OCP EMEA Summit 2025 in the DC Physical Infrastructure track. It covers adding cold-plate cooling to the vertical 48 V busbar of an Open Rack V3 (ORv3) so that it can carry far more current in the same envelope. The deck lists the design limits: temperature rise of at most 30 C, voltage drop of at most 0.1 V, no leakage, no contact between coolant and copper, and quick-connect serviceability.

According to the comparison table, the air-cooled ORv3 busbar is 36 kW, 750 A, 150 mm2 conductor and about 14 kg, while ORv3 HPR is 140 kW, 2916 A, 1600 mm2 and about 80 kg. The liquid-cooled 200 kW busbar carries 4166 A with only a 212 mm2 conductor at about 16 kg in the standard ORv3 footprint; the liquid-cooled 750 kW busbar is 15,625 A, 1483 mm2 and about 85 kg. Liquid cooling raises current-carrying capacity about 5x in the same form factor, and 1 MW+ designs are in work.

Simulation and bench tests show that voltage drop rather than temperature rise limits the smaller liquid-cooled design: 7.8 C rise at 0.1 V drop at 200 kW, 18 C and 0.15 V at 300 kW, and 33.6 C and 0.21 V at 400 kW. Connections use off-the-shelf barbed fittings, 3/8 in EPDM hose and UQD04 sockets mating to the rack manifold, and simulations used PG25 coolant at 25 C inlet. This is a conference deck, so detailed reasoning sits in the spoken part of the talk.

Key points

1. Design criteria: busbar temperature rise max 30 C, voltage drop max 0.1 V, no leakage or coolant-copper contact, quick-connect serviceability.
2. Air-cooled ORv3 busbar: 36 kW, 750 A, 150 mm2, about 14 kg; ORv3 HPR: 140 kW, 2916 A, 1600 mm2, about 80 kg.
3. Liquid-cooled 200 kW busbar: 4166 A with only 212 mm2 conductor, about 16 kg, in the standard ORv3 footprint.
4. Liquid-cooled 750 kW busbar: 15,625 A, 1483 mm2, about 85 kg.
5. Liquid cooling raises current-carrying capacity about 5x in the same form factor; 1 MW+ designs are in work.
6. Simulated 200 kW busbar: 7.8 C rise at 0.1 V drop; 300 kW gives 18 C and 0.15 V; 400 kW gives 33.6 C and 0.21 V; the 200 kW rating is set by voltage drop.
7. Connections: off-the-shelf barbed fittings, 3/8 in EPDM hose, UQD04 sockets to the rack manifold; simulations used PG25 at 25 C inlet.

Using it in design

• Give rack power distribution components fields for rated current, maximum voltage drop and cooling method.
• Check total rack DC current against the busbar rating, warning above 750 A for standard air-cooled ORv3 busbars.
• For liquid-cooled busbars, add their flow to the rack manifold coolant budget.

Who should read it

Electrical and mechanical engineers sizing busbars and in-rack power distribution at AI rack power levels.

Related standards

• OCP Open Rack V3 Base Specification
• OCP ORv3 HPR
• OCP UQD

Publication details

Authors

Hal Loket; Lily Zhang; Brian Costello; Roger Luo; Dmitriy Shapiro; John Fernandes

Publisher

Open Compute Project Foundation

Year

2025

Document number

OCP EMEA Summit 2025, DC Physical Infrastructure track

Event

OCP EMEA Summit 2025, Dublin

Document language

English

Source type

Industry body

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation