Resources / Glossary

Glossary.

Buyer-facing definitions for the acronyms and standards that show up in a modular data center or power infrastructure quote. Plain-English. Standards-body usage where one exists. Not marketing copy.

A

AD/CVD

Anti-Dumping and Countervailing Duties. Case-specific tariffs imposed by the US Department of Commerce (with International Trade Commission injury determinations) on imports priced below fair market value or supported by foreign government subsidies. Stack on top of standard MFN duties and any Section 232 / 301 charges.

ASHRAE A1 / A2 / A3 / A4

ASHRAE TC9.9 thermal-environment classes for IT equipment. A1 (15–32°C, the conservative legacy class) progresses through A4 (5–45°C, the wide ambient envelope used by free-cooling-aggressive designs). Modular DCs that operate confidently at A4 can deploy in hot-climate or fan-economized sites without mechanical chillers running year-round.

ASHRAE W1 / W2 / W3 / W4

ASHRAE TC9.9 liquid-cooling supply-water temperature classes for direct-liquid-cooling (DLC) systems. W1 (2–17°C) requires chilled-water plant; W4 (up to 45°C) accepts warm-water cooling and unlocks dry-cooler or adiabatic heat-rejection without compressors. W4 capability is a precondition for high-density (>40 kW/rack) deployment in hot climates.

ATS — Automatic Transfer Switch

A switch that detects loss of utility power and transfers the load to a backup source (typically a genset) within a defined window. Open- and closed-transition variants. Sized in amps; coordinated with upstream switchgear and the backup source's start time.

B

BAA — Buy American Act

1933 federal-procurement law applicable to direct US-government purchases. As amended, requires 65% domestic content for end products through 2028, rising to 75% effective January 1, 2029. Distinct from BABA, which applies to federally-assisted (not directly procured) infrastructure. End-product cost-of-components test, not value-added.

BABA — Build America, Buy America

Title IX of the Infrastructure Investment and Jobs Act (2021), implementing 2 CFR Part 184. Applies to federally-assisted infrastructure projects and requires that iron, steel, manufactured products, and construction materials be produced in the United States. Manufactured-products threshold is currently 55% (cost of US components ÷ total component cost), with a roadmap to 60% then 65%. Waivers exist; they are public.

BMS — Building Management System

Software and controller stack that supervises HVAC, lighting, fire alarm, access, and life-safety equipment in a building. In a data hall the BMS sits alongside DCIM and SCADA — BMS owns building services, DCIM owns IT-asset and rack-power telemetry, SCADA owns electrical-system monitoring and control.

C

CBP — US Customs and Border Protection

Federal agency that classifies imported goods under the HTSUS at the port of entry, assesses duties, and enforces trade-remedy orders. Importers reduce classification risk by requesting a binding ruling letter under 19 CFR Part 177 before shipment.

CDU — Coolant Distribution Unit

The pump-and-heat-exchanger module in a direct-liquid-cooling loop that isolates the rack-side coolant (technical fluid, tight tolerance) from the facility-side water (broader chemistry, higher temperature). One CDU typically serves 1–4 racks in retrofit topologies and a row in greenfield ones.

CIF — Cost, Insurance, Freight

An Incoterm and customs-valuation basis: the seller pays freight and insurance to the named US port. CBP applies duty rates against the CIF value, not the EXW (factory-gate) price. The freight and insurance line items inflate the dutiable base by 5–15% for ocean cargo from Europe.

CRAC / CRAH — Computer Room Air Conditioner / Air Handler

Perimeter cooling units that supply chilled or cooled air to a raised-floor or hot-aisle/cold-aisle data hall. CRAC contains its own compressor; CRAH uses chilled water from a central plant. Largely supplanted by in-row and rear-door cooling at densities above 20 kW/rack and by direct-liquid-cooling above 40 kW/rack.

D

DCIM — Data Center Infrastructure Management

Software stack that monitors and reports on rack power, environmental conditions, asset inventory, and capacity at the IT-equipment level. Integrates with BMS (building services) and SCADA (electrical) to give a single operator view. Common open standards: Redfish, IPMI, SNMP, BACnet, Modbus.

DDP / EXW — Delivered Duty Paid / Ex Works

Two opposite-end Incoterms. EXW: buyer takes the goods at the seller's factory gate and assumes all transport, customs, and risk. DDP: seller delivers the goods to the buyer's named site with all duties and clearance paid. The Incoterm chosen determines which party absorbs the trade-policy risk between PO and delivery.

DLC — Direct Liquid Cooling

Cooling architecture in which a technical fluid (water-glycol or single-phase dielectric) is delivered directly to a cold-plate on the GPU, CPU, or memory package. Required above approximately 40 kW/rack and standard above 80 kW/rack. Plumbing complexity, leak-management, and CDU sizing are the three procurement questions that drive total installed cost.

F

FAT / SAT — Factory / Site Acceptance Test

FAT is a witnessed test sequence run at the manufacturer's plant before shipment — confirms electrical, thermal, and control behavior under simulated load. SAT is the mirror sequence run at the customer's site after install, before commercial operation date. Both produce signed test reports that are condition precedents to PO milestones.

FTZ — Foreign Trade Zone

A US area treated as outside CBP territory for duty purposes. Goods can be admitted, stored, manipulated, and re-exported without paying US duties; goods entered into US commerce pay duty at the time of withdrawal. Useful for duty deferral, inverted-tariff (paying the lower of the input or finished-good rate), and re-export scenarios.

G

GSA Schedule (MAS) — Multiple Award Schedule

General Services Administration's pre-negotiated, indefinite-delivery contract vehicle covering commercial products and services for federal civilian and (with caveats) defense buyers. Vehicle for TAA-eligible goods. Industrial Funding Fee of 0.75% of all schedule sales. The Most-Favored-Customer / Price Reduction Clause is the largest compliance trap.

H

HTS / HTSUS — Harmonized Tariff Schedule of the United States

The classification system US importers use to declare goods at entry. Each product receives a 10-digit HTS number that determines the MFN duty rate, Section 232 / 301 applicability, and AD/CVD exposure. Modular building units of steel classify under heading 9406; switchgear under 8537; transformers under 8504; gensets above 375 kVA under 8502.13.

I

IEC 61439

International standard for low-voltage switchgear and controlgear assemblies. Subdivides into 61439-1 (general rules) and 61439-2 (power switchgear). Compliance is verified against a Type Test (now called design verification) on a representative assembly. Equivalent in scope to UL 891 in North America; the two are not interchangeable but both attest to the same safety functions.

IEC 62271

International standard for high-voltage switchgear and controlgear (rated above 1 kV AC). Multi-part series covering AIS and GIS designs, circuit breakers, disconnectors, and gas-insulated metal-enclosed assemblies. The reference standard for medium-voltage substations sized for utility interconnect at 6–35 kV.

IEEE C37

Institute of Electrical and Electronics Engineers C37 standards series for power switchgear, switching apparatus, and protective relays. The North American counterpart layer to IEC 62271 for high-voltage equipment; many utility specifications cite C37 ratings (e.g., C37.06 for circuit-breaker preferred ratings).

ISO 9001

International quality-management-system standard. Certification is awarded after audit by an accredited third-party registrar and renewed on a three-year cycle with annual surveillance. Often required by procurement as a minimum-quality gate for industrial equipment vendors.

K

kW/rack — kilowatts per server rack

Density measure: the IT-equipment power load a single server rack supports under continuous operation. Air-cooled rear-door designs typically top out at 20–40 kW/rack; direct-liquid-cooled designs run 40–150 kW/rack in current production with reference designs at 120+ kW/rack for the latest GPU SKUs.

M

MV / LV — Medium / Low Voltage

IEC nomenclature: low voltage is up to 1 kV AC; medium voltage is roughly 1–35 kV AC (with regional definitions varying). Data hall service typically lands at MV from the utility, drops to 480 V LV at a step-down transformer, and distributes through low-voltage switchgear and PDUs to the rack.

N

NCP — NVIDIA Cloud Partner

NVIDIA program of reference architectures for GPU-cloud operators. The Reference Architecture documents specify rack power, cooling, network fabric, storage, and orchestration components for H100 / H200 / B200 / GB200 NVL72 and successor SuperPOD-class deployments. Buyers building neocloud capacity often anchor RFIs on NCP RA conformance.

NFPA 70 / 75 / 110

National Fire Protection Association codes relevant to data centers. NFPA 70 is the National Electrical Code (NEC), the basis of US electrical-installation safety. NFPA 75 covers fire protection of information-technology equipment. NFPA 110 covers emergency-and-standby power systems including gensets, fuel storage, and transfer switches.

NRTL — Nationally Recognized Testing Laboratory

OSHA-recognized third party (UL, Intertek/ETL, CSA, TÜV, etc.) authorized to test and certify electrical equipment to applicable US safety standards. NRTL listing is the practical pathway for IEC-certified equipment to enter US commerce — the assembly is re-evaluated against UL or equivalent and given a US listing mark.

P

PUE — Power Usage Effectiveness

Defined by The Green Grid (now ASHRAE TC9.9): total facility energy ÷ IT-equipment energy. A PUE of 1.0 is the theoretical minimum; modern air-cooled facilities target 1.3–1.5; well-designed DLC facilities target 1.05–1.15. Comparison only fair when measurement methodology, ambient assumption, and load factor are stated.

S

SCADA — Supervisory Control and Data Acquisition

Industrial-control software architecture for monitoring and controlling electrical and mechanical infrastructure. In a data hall the SCADA layer sits over substation, switchgear, UPS, and genset controllers, exposing protective-relay events, breaker positions, and load flows to operators. Common protocols: DNP3, IEC 61850, Modbus.

Section 232

Trade Expansion Act of 1962, 19 USC §1862. Authority for the President to impose tariffs on imports judged to threaten national security. Currently active on steel, aluminum, and copper at rates that have varied over 2018–2026. Modular building units of steel (HTS 9406.20) were added to the Section 232 derivative list on August 18, 2025.

Section 301

Trade Act of 1974, 19 USC §2411. Authority for the US Trade Representative to impose tariffs in response to foreign trade practices. The active 301 program targets China-origin goods on Lists 1–4A at 7.5%–25%. A finished good substantially transformed in a non-China country is not Section-301-exposed at US entry, even if some component inputs originated in China.

Section 889

NDAA FY2019 §889 (Pub. L. 115-232). Bans federal agencies and federal contractors from using or providing covered telecommunications equipment from Huawei, ZTE, Hytera, Hangzhou Hikvision, Dahua, or affiliates — applies to all components, including embedded video and surveillance subsystems. Compliance attestation is a federal-deal-killer if not cleared early.

T

TAA — Trade Agreements Act

Trade Agreements Act of 1979. Governs eligibility of foreign-origin goods for federal civilian procurement under the GSA Schedule and similar vehicles. Uses a substantial-transformation standard, not a value-added percentage. The list of TAA-designated countries is published by USTR.

Tier I–IV — Uptime Institute classification

Uptime Institute's four-level classification of data-center site infrastructure. Tier I: basic capacity, no redundancy. Tier II: redundant capacity components. Tier III: concurrently maintainable (any single component can be taken offline without disrupting IT load). Tier IV: fault-tolerant. Modular and prefabricated designs typically certify to Tier II or Tier III equivalent at the module level; full Tier IV requires 2N power and cooling topologies.

TTA — Type-Tested Assembly

An IEC 61439 design that has passed the full set of type-test (now called design-verification) requirements on a representative sample, including temperature-rise, short-circuit, dielectric, and IP-degree tests. TTA evidence is the buyer-side gate that distinguishes a proper switchgear assembly from a custom panel assembled to lower standards.

U

UL 489

Underwriters Laboratories standard for molded-case circuit breakers, molded-case switches, and circuit-breaker enclosures. The component-level standard a US-listed branch breaker must satisfy. Pairs with UL 891 (the assembly-level switchboard standard) at the panel level.

UL 891

Underwriters Laboratories standard for dead-front switchboards rated up to 1000 V AC or 1500 V DC. The North American counterpart layer to IEC 61439-1/-2 for low-voltage assemblies. UL 891 is what most US authorities-having-jurisdiction expect to see; an IEC-tested assembly typically reaches UL 891 listing through a dual-cert path with an NRTL.

UPS — Uninterruptible Power Supply

Battery- or flywheel-backed power conditioner that bridges the load between a utility-power loss and the start of standby generation. Sized in kVA / kW with an associated runtime (typically 5–15 minutes). Topologies: standby (cheapest, slowest), line-interactive, and double-conversion online (cleanest output, used in production data halls).

Definitions reflect standards-body language and industry practice as of Q2 2026. The full internal glossary (including venture-specific shorthand) is maintained in the Teraplex wiki.

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