Keep the Gray Space Gray
The Engineering, Safety, Cybersecurity, and Compliance Case Against Co-Locating 800 V DC Power Infrastructure Inside the IT White Space of AI-Era Data Centers
Foreword: A Message from the Operations Side of the House
For the last twenty-five years, I have watched data centers grow up from the closet, to the raised-floor computer room, to the enterprise hall, to the colocation hall, to the multi-hundred-megawatt hyperscale campus, and now to the gigawatt-class AI factory. In that time, I have rarely seen a debate about how and where to locate electrical and cooling infrastructure that did not eventually converge on the same answer: put it in a gray space, on the other side of a rated wall from the servers, operated and maintained by electrically qualified personnel under a separate chain of access, documentation, and inspection.
That convergence was not a fashion. It is a lesson stamped into us by decades of near-misses, outages, and a handful of irreversible tragedies. It is a lesson reinforced by TIA-942, by the Uptime Institute Tier classifications, by BICSI 002, by NFPA 75 and NFPA 76, by the National Electrical Code, and by the hard-won behaviors that an experienced site lead insists upon before any contractor crosses a threshold with a tool bag.
The white paper “800-VDC Data Centers and the Central Role of Solid-State Transformers,” authored by Peter Sopher and published by DG Matrix in advocacy of their multi-port solid-state transformer and “SideCar” platform, is an articulate and ambitious piece of electrical engineering thought leadership. It is also, in its current expression, a prescription for architectural regression. Its diagrams unambiguously place medium-voltage and kilovolt-DC conversion equipment, and lithium-ion / super-capacitor energy-storage modules, inside the IT white space. It does so explicitly: the legend in the company’s own figures labels “SideCar (3-Port)” and “Super Caps / High Cycle Battery” with a “W” for White Space.
The AI era is being built, at an extraordinary pace, by people who are not always the people who will operate it on day 2. The designers of these new 800 V DC platforms are, in many cases, brilliant power-electronics engineers with a deep understanding of converter topologies and a shallow understanding of data-center operations culture, compliance scoping, and the consequences of blurring the line between the IT environment and the energy-conversion environment. This white paper is a deliberate pushback, written from the operations side of the house, intended to inform not just the buyers and owners of next-generation infrastructure, but also the designers themselves, who—to their enormous credit—are willing to publish their architecture and defend it in the open.
We are not opposed to 800 V DC. We are not opposed to solid-state transformers. We are not opposed to colocation of high-density load and primary conversion. We are opposed to putting unqualified people, qualified people doing unqualified work, energized medium-voltage conversion stages, and thermal-runaway-capable storage cells, behind the same door, on the same floor, in the same airflow, and under the same access badge as the servers they power. That is the architecture DG Matrix proposes, and it is the architecture this paper rejects.
If this document achieves only one thing, let it be this: that when a hyperscale buyer, a colocation architect, or a critical facilities engineer is handed a proposal that places SideCars, SSTs, and high-cycle batteries inside the white space, they respond with the same five questions—each well-grounded in code, standard, and scar tissue—that Part VIII of this document provides.
Executive Summary
This white paper examines and rejects the architectural approach proposed by DG Matrix in its 2024–2025 white paper on 800-VDC data centers, in which solid-state transformers (SSTs), medium-voltage-capable SideCar conversion stages, super-capacitor banks, and high-cycle battery packs are deployed inside the IT white space of AI-era data centers. The analysis is organized into eight substantive parts and a set of appendices. The overall conclusion is that the DG Matrix architecture, as drawn in its own figures, violates long-standing gray/white space separation doctrine; creates unresolved conflicts with NEC Article 110.26 and 110.34 working space, NFPA 70E arc flash methodology, NFPA 75/76 fire separation, NFPA 855 energy-storage separation, and TIA-942-C space classification; forces unqualified IT personnel into proximity with medium-voltage and kilovolt-DC hazards; forces electrically qualified personnel into proximity with data-bearing IT equipment in ways that violate least-privilege and separation-of-duties; materially expands the cyber attack surface in ways that the Target 2013 breach should have taught the industry are unacceptable; and degrades, rather than improves, the concurrent maintainability and fault tolerance promised by the Uptime Institute Tier framework.
Ten Findings in Ten Sentences
1. DG Matrix’s own architecture diagrams place SideCar conversion stages and high-cycle battery / super-capacitor modules inside the White space, indistinguishable in placement from IT racks.
2. This placement breaks the doctrinal separation between gray space (power, cooling, mechanical) and white space (IT), a separation that is required or strongly recommended by TIA-942-C, Uptime Institute Tier Standard, BICSI 002-2024, and every major compliance framework that addresses physical scoping.
3. Under NEC Article 110.26(A)(1) and 110.34, medium-voltage and kilovolt-DC equipment requires working clearances and dedicated egress that are fundamentally incompatible with the hot-aisle/cold-aisle and row-based layouts of an IT hall.
4. NFPA 70E 2024 arc-flash, shock, and limited-approach-boundary requirements cannot be honored when the boundary surrounds an IT rack being serviced by a storage administrator with no electrical qualification.
5. Direct current at 800 V and above does not cross zero sixty or fifty times per second; DC fault currents must be interrupted under conditions that classical IEEE 1584-2018 arc-flash math does not cover, and the industry’s practical tooling and PPE for DC arc-flash remains immature relative to AC.
6. Lithium-ion and super-capacitor failure modes, documented at McMicken (2019), Moss Landing (2024), and multiple Korean and Chinese data-center incidents, produce vented gases, thermal runaway, and reignition profiles that NFPA 855 and UL 9540A explicitly accommodate by requiring physical separation from non-storage occupancies.
7. The 2013 Target breach, traced to Fazio Mechanical Services—an HVAC vendor—demonstrated, at industry-defining cost, that the people who walk mechanical and electrical infrastructure into your building carry credentials, tools, and habits that belong to a different risk class than those of the IT staff who run the workloads.
8. Modern compliance regimes—NIST SP 800-53 PE family, NIST SP 800-207 Zero Trust, ISO/IEC 27001:2022 Annex A.7, PCI-DSS v4.0 Req. 9, HIPAA 164.310, FedRAMP, SOC 2 CC6—all assume, and in most cases require, that physical scoping be cleanly drawn around the information system; when your power conversion lives inside that scope, so does every vendor technician who services it.
9. The argument that “we must put conversion inside the white space to chase efficiency” collapses under scrutiny: the marginal efficiency difference between an adjacent-gray-space conversion line and an in-row conversion line, with modern busway, is dwarfed by the risk, operational cost, and scope inflation created by the in-row placement.
10. The correct architecture is an adjacent but separate gray space, with MV/DC conversion, storage, and switching operated and maintained by qualified personnel under a disciplined access regime, connected to the white space by a hardened DC bus that is itself the only thing that crosses the wall.
What This Paper Is Not
This paper is not a rejection of 800 V DC. The thermodynamic, cabling, and integration arguments for a higher DC distribution voltage in AI-class racks are real and worth taking seriously. The Open Compute Project Open Rack V3 work, the EMerge Alliance 380 V DC occupant-space guidance, and a generation of published research on HVDC data center power argue credibly that the facility distribution voltage should rise. The question this paper asks is a different question: where should the equipment that produces, stores, and switches that voltage live, and who should be allowed to touch it?
This paper is not a vendor bake-off. DG Matrix’s SST program is one instance of a broader trend. Other firms, including incumbents and start-ups, are exploring similar architectures. This paper uses the DG Matrix paper as a concrete reference because (a) it is the most explicit and well-drawn example publicly available at the time of writing, and (b) Mr. Sopher and DG Matrix deserve engagement on the merits rather than innuendo. The points made here apply equally to any vendor that proposes the same architectural pattern.
This paper is not a claim that white-space-side power conditioning is always wrong. Rack-level PDUs, bus-bar taps, and last-mile DC/DC converters at the 48-V and 54-V classes are mature and safe, and belong inside the rack. What does not belong inside the rack is anything capable of delivering arc-flash energy that requires an NFPA 70E risk assessment, anything whose failure mode includes thermal runaway of cells at the multi-kilowatt-hour class, or anything whose installation, test, commissioning, and routine maintenance require a qualified electrical worker, a shock boundary, or a PPE category above Category 1.
Organization of This Paper
Part I reviews the gray/white space doctrine: where it came from, why it exists, and the twelve operational dimensions along which the two environments differ. Part II walks through the electrical codes and standards that apply: NEC Articles 110, 409, 450, 480, 645, 706, and 710; NFPA 70E 2024; NFPA 75 and 76; NFPA 855; TIA-942-C; BICSI 002-2024; Uptime Institute Tier Standard: Topology. Part III addresses the physics and practical safety of 800 V DC: body-current effects per IEC 60479-1, zero-crossing and fault clearing, the limits of IEEE 1584-2018 at DC, super-capacitor stored energy, and the state of DC-rated PPE and overcurrent devices. Part IV addresses cybersecurity implications, including the Fazio/Target vector in detail, the NIST 800-53 PE family mapping, zero-trust physical access, separation of duties, principle of least privilege, and the sector-specific compliance obligations (PCI, HIPAA, FedRAMP, SOC 2, CMMC, NIS2). Part V addresses operational standards: change control, LOTO, MOPs/EOPs/SOPs, concurrent maintainability, and how in-white-space power infrastructure structurally undermines each. Part VI documents historical incidents—power, fire, cooling, and cyber—where the failure vector was a contractor, technician, or facilities worker, and traces each one to a lesson that the DG Matrix architecture ignores. Part VII sets out the correct architecture and enumerates the design principles that govern it. Part VIII offers consolidated recommendations mapped to codes and frameworks. The appendices provide a glossary, a summary of unanswered questions for any vendor proposing this architecture, and a standards index.
Full white paper below
