Glossary

Welcome to the USPWR Glossary, your go-to reference for understanding the technologies, terminologies, and infrastructure components that shape modern low voltage power distribution systems in mission-critical environments like data centers, telecom facilities, and enterprise campuses.

A-C

Ampacity
The maximum amount of electrical current a conductor or device can carry before sustaining immediate or progressive deterioration. Ampacity is influenced by conductor size, insulation type, ambient temperature, and installation conditions.

Automatic Transfer Switch (ATS)
A device that automatically switches electrical loads between two power sources, typically from utility to generator, ensuring continuous operation during outages. Unlike Static Transfer Switches, ATS systems often include mechanical switching and brief transfer delays.

Backup Power
Any system that provides electrical power during utility outages. This includes Uninterruptible Power Supplies (UPS), generators, and battery storage systems—all integral to ensuring uptime in Tier III and IV data centers.

Branch Circuit Monitoring
The most granular level of power monitoring available in floor-standing PDUs, branch circuit monitoring tracks power consumption and performance metrics at the individual circuit level. This capability enables data center operators to identify inefficiencies, optimize load balancing, and detect potential issues before they escalate, thereby improving operational reliability and energy efficiency.

Busway (or Bus Duct)
A modular, overhead or underfloor power distribution system consisting of insulated conductors enclosed in a metal housing. Busways offer scalability, reduced cable clutter, and ease of maintenance compared to traditional cabling.

Circuit Breaker
An automatically operated electrical switch designed to protect a circuit from damage due to overload or short circuit. Circuit breakers can be integrated into RPPs, PDUs, or main switchgear assemblies.

Colocation Data Center
A facility where multiple organizations share infrastructure, including power distribution and cooling systems, to house their IT equipment. Colocation centers require PDUs with outlet-level metering for billing accuracy, enabling precise tracking of power usage by individual tenants. Eaton’s PDUs, for example, support such environments with configurable, high-accuracy metering capabilities.

Critical Load
Any device, server, or system whose failure would compromise the mission of the data center or IT environment. Power infrastructure must prioritize redundancy and fault tolerance for these loads.

D-H

Daisy Chaining
A method of connecting multiple PDUs to share a single IP address, reducing network infrastructure costs and simplifying remote management. Up to eight Eaton Metered Input PDUs can be daisy-chained, allowing centralized control and monitoring of multiple power supplies with a single command, enhancing scalability and operational efficiency.

Demand Factor
The ratio of actual power consumed to the maximum possible load. This metric is vital for capacity planning, especially when designing UPS and PDU specifications.

Distribution Panel
Also referred to as Remote Power Panel (RPP), it provides circuit-level power distribution to IT racks or other loads. RPPs often include metering, circuit breakers, and branch-level monitoring.

Downtime (Planned vs. Unplanned)
Planned downtime refers to scheduled outages for maintenance; unplanned refers to unexpected outages due to failure. Power systems are designed to minimize both, especially unplanned disruptions.

ePDU G3 Technology

Eaton’s third-generation power distribution unit technology, featured in rack-mounted PDUs, offering advanced capabilities such as outlet-level metering, switching, and universal input compatibility. ePDU G3 PDUs support diverse IT environments, from small businesses to enterprise data centers, with features like tool-less installation, high operating temperatures, and integration with management software for real-time monitoring and automation.

Energy Efficiency

A measure of how effectively a data center power distribution system minimizes energy waste while delivering reliable power. Efficient systems, such as those incorporating three-phase PDUs or lithium-ion UPS batteries, reduce operating costs and environmental impact. Eaton’s solutions, for instance, emphasize energy-efficient designs to support sustainable data center operations.

Form Factor
The physical configuration of a PDU or UPS, typically described in terms of rack units (U or RU) or mounting orientation (e.g., 0U for vertical, 1U or 2U for horizontal). Form factor impacts space utilization and installation flexibility. For example, vertical PDUs save rack space and provide more outlets, while horizontal PDUs occupy standard rack units.

Harmonics
Distortions in the AC power waveform caused by nonlinear loads (e.g., servers, variable frequency drives). High harmonic distortion can lead to overheating, reduced efficiency, and equipment failure, requiring filtering or harmonic mitigation.

High Density (HD) PDU
A rack-mounted PDU designed for environments with concentrated power demands, such as enterprise data centers. HD PDUs, like Eaton’s HD Metered Outlet and HD Managed models, offer configurability, outlet-level metering, and switching capabilities. They support rapid deployment with tool-less installation and integrate with management platforms for enhanced control and monitoring.

I-M

Intelligent PDU (iPDU)
A Power Distribution Unit equipped with features such as remote power monitoring, outlet-level switching, and environmental sensors. iPDUs are central to intelligent infrastructure management and PUE optimization.

Intelligent Power Management Platform
A software solution that integrates with networked PDUs and UPS systems to provide comprehensive monitoring, control, and automation of power infrastructure. Eaton’s Intelligent Power Management Platform, compatible with Metered Input, Metered Outlet, and Managed PDUs, enables remote management via web or SNMP protocols, offering insights into power usage, predictive maintenance, and cybersecurity updates.

Isolation Transformer
A device used to decouple two circuits for safety, noise reduction, or voltage adjustment. In UPS systems, isolation transformers can also mitigate harmonics and improve power quality.

Load Balancing
The even distribution of electrical load across available phases or circuits to ensure system efficiency and avoid overloading. It’s a critical component of system design in three-phase environments.

Lithium-Ion UPS Battery
A power storage solution for UPS systems that uses lithium-ion chemistry, offering advantages over traditional lead-acid batteries, including longer lifespan, smaller footprint, and higher energy density. Lithium-ion batteries reduce maintenance costs and improve energy efficiency, making them suitable for modern data centers prioritizing sustainability and space optimization.

Maintenance Bypass
A system that allows power to bypass a UPS during maintenance or replacement without interrupting power to connected equipment. Maintenance bypasses enhance redundancy and reliability in backup power systems, providing a cost-effective alternative to fully redundant setups. Best practices include proper installation to ensure seamless operation during power source transitions.

Mean Time Between Failures (MTBF)
A reliability metric representing the average time a system or component operates before failing. High MTBF values indicate robust engineering—an essential benchmark in mission-critical power systems.

Metered Input PDU
A PDU that measures and reports power consumption at the input level, providing data center operators with insights into overall power usage. Metered Input PDUs support daisy-chaining and remote management, reducing infrastructure costs and enabling proactive load management. Eaton’s models include features like IEC outlet grips and high operating temperature tolerance.

Metered Outlet PDU
A PDU that monitors power consumption at the individual outlet level, offering granular data for billing, load balancing, and performance optimization. These PDUs are critical in colocation data centers, where precise metering ensures accurate allocation of power costs among tenants. Eaton’s Metered Outlet PDUs integrate with management software for enhanced control.

Modular UPS
A scalable, hot-swappable Uninterruptible Power Supply system where individual power modules can be added or replaced without system shutdown. Ideal for growing data centers.

N-R

N+1 Redundancy
A fault-tolerant architecture that includes one additional component beyond what is necessary for operation (e.g., one extra UPS module). Ensures continued operation even if a single component fails.

Neutral Conductor
A conductor that carries current in a balanced three-phase system and completes the electrical circuit. Correct sizing and routing are vital for mitigating harmonic issues and ensuring safe system operation.

Overcurrent Protection
A system of devices, such as fuses and breakers, designed to protect circuits from excessive current which can cause equipment damage or fire hazards.

PDU (Power Distribution Unit)
A device used to distribute electric power to racks and IT equipment. PDUs range from basic units to advanced intelligent PDUs with monitoring, switching, and environmental sensing capabilities.

Power Factor
A measure of how effectively incoming power is used. A low power factor (closer to 0 than 1) indicates poor efficiency and may incur utility penalties. Correction methods include capacitors or UPS features.

Rack PDU (rPDU)
A form factor of PDU that mounts directly to server racks. These devices can be basic or intelligent, single-phase or three-phase, and are critical for modern rack-level energy management.

Remote Power Panel (RPP)
An electrical panel that delivers branch circuit power to IT racks, typically fed from a PDU or switchgear. RPPs allow flexible distribution and typically include circuit-level monitoring and protection.

S-Z

Scalability
The capability of power infrastructure (e.g., modular UPS, busway) to grow in capacity without requiring wholesale replacement. A key driver for modern distributed architecture.

Single-Phase PDU
A PDU that receives and distributes power using a single electrical phase, suitable for smaller data centers or low-power applications. Single-phase PDUs are simpler and less costly than three-phase PDUs but have lower capacity, making them ideal for network closets or small server rooms.

Single Point of Failure (SPOF)
Any component in the power path whose failure would cause a total system outage. Redundancy strategies are designed to eliminate SPOFs in high-availability environments.

Static Transfer Switch (STS)
An electronic device that switches between two power sources (typically utility and generator) in milliseconds without interrupting the load. STSs are used to eliminate power interruptions during source transitions.

Surge Protection Device (SPD)
Protects sensitive electronics from voltage spikes typically caused by lightning or switching surges. Integrated into PDUs, UPS systems, or at the service entrance.

Three-Phase Power
A method of AC power distribution used for efficiency and balance in industrial and data center environments. It allows for higher power density compared to single-phase power.

Total Harmonic Distortion (THD)
A metric indicating the level of harmonic distortion in a system. Low THD is desirable and often a performance specification for UPS or PDU systems in sensitive IT environments.

Uninterruptible Power Supply (UPS)
A battery-backed power device that provides uninterrupted power to critical systems during outages or fluctuations. Types include double-conversion (online), line-interactive, and standby models.

Universal Input PDU (UPDU)
A PDU with interchangeable input cables that support multiple plug types, enabling compatibility with diverse electrical standards across regions and applications. UPDUs reduce equipment costs and deployment time by allowing a single PDU chassis to adapt to various power configurations, enhancing flexibility in global data center operations.

Uptime Institute Tiers
A standardized classification (Tier I–IV) defining data center reliability, redundancy, and uptime expectations. Tier III and IV facilities demand advanced, redundant power distribution strategies.

Voltage Drop
A decrease in voltage along a conductor due to resistance. Can lead to inefficiencies or equipment malfunction, particularly in long cable runs or undersized conductors.

Zone Distribution
A strategic power distribution layout in large facilities where power is distributed to zones (each served by RPPs or localized PDUs), reducing cabling complexity and improving load management.

Final Notes

This glossary is curated to support decision-makers, engineers, and operations professionals as they engage with the complex and mission-critical world of power distribution infrastructure. Understanding these terms ensures effective communication, strategic planning, and robust implementation of high-availability systems.

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