White Papers


ATTENTION: For instructions on how to properly link to these white papers. click here 60 result(s) found.
Number Title & Abstract
WP-206 v0
Overload Protection in a Dual-Corded Data Center Environment
In a dual-corded environment, the loss of power on one path will cause the load to transfer to the other path, which can create an overload condition on that path. This can lead to a situation where the failure of one path leads to the failure of both paths. This paper explains the problem and how to solve it, and provides a set of rules to ensure that a dual-path environment provides the expected fault tolerance.
WP-129 v3
Comparing Data Center Power Distribution Architectures
Significant improvements in efficiency, power density, power monitoring, and reconfigurability have been achieved in data center power distribution, increasing the options available for data centers. This paper compares five power distribution approaches including panelboard distribution, field-wired PDU distribution, factory-configured PDU distribution, floor-mount modular power distribution, and modular busway, and describes their advantages and disadvantages. Guidance is provided on selecting the best approach for specific applications and constraints.
WP-165 v0
Types of Prefabricated Modular Data Centers
Data center systems or subsystems that are pre-assembled in a factory are often described with terms like prefabricated, containerized, modular, skid-based, pod-based, mobile, portable, self-contained, all-in-one, and more. There are, however, important distinctions between the various types of factory-built building blocks on the market. This paper proposes standard terminology for categorizing the types of prefabricated modular data centers, defines and compares their key attributes, and provides a framework for choosing the best approach(es) based on business requirements.
WP-127 v4
A Quantitative Comparison of High Efficiency AC vs. DC Power Distribution for Data Centers
This paper presents a detailed quantitative efficiency comparison between the most efficient DC and AC power distribution methods, including an analysis of the effects of power distribution efficiency on the cooling power requirement and on total electrical consumption. The latest high efficiency AC and DC power distribution architectures are shown to have virtually the same efficiency, suggesting that a move to a DC-based architecture is unwarranted on the basis of efficiency.
WP-210 v0
Single Phase UPS Management, Maintenance, and Lifecycle
“How long will my battery last?” and “what is the best practice for maintaining my UPS?” are very common questions posed from UPS owners. Few realize there is more to the UPS than just battery back-up; and that, like all electronics it has a life expectancy. Many of the factors that affect battery life also affect UPS electronics. Some factors may be controlled by taking some preventative measures or simply adjusting some basic UPS settings. This whitepaper discusses the key factors that influence both battery and UPS life; and provides some simple recommendations and guidelines to help you manage your single phase UPS to maximize the life and overall availability.
WP-151 v0
Review of Four Studies Comparing Efficiency of AC and DC Distribution for Data Centers
DC is proposed for use in data centers as an alternative to AC distribution primarily based on publicized claims of efficiency improvements and energy savings. This paper shows that the most widely cited values for quantitative improvements are wrong and grossly overstate the efficiency differences between AC and DC, and that the latest AC and DC systems provide effectively the same efficiency. This paper compares the results of four different publicized studies and explains the assumptions and mistakes that have led to erroneous but widely circulated beliefs about the efficiency benefits of DC power distribution.
WP-207 v0
Design and Specification for Safe and Reliable Battery Systems for Large UPS
A properly designed UPS battery solution is important for safe and reliable operation. This paper describes the main components and functions of a battery system, and discusses the reasons why vendor pre-engineered battery solutions are optimal. In cases where pre-engineered solutions don’t meet the requirements, vendor-engineered solutions are next best. If third party custom battery solutions must be used, design guidelines are provided to ensure a safe and reliable design.
WP-118 v4
Virtualization and Cloud Computing: Optimized Power, Cooling, and Management Maximizes Benefits
IT virtualization, the engine behind cloud computing, can have significant consequences on the data center physical infrastructure (DCPI). Higher power densities that often result can challenge the cooling capabilities of an existing system. Reduced overall energy consumption that typically results from physical server consolidation may actually worsen the data center’s power usage effectiveness (PUE). Dynamic loads that vary in time and location may heighten the risk of downtime if rack-level power and cooling health are not understood and considered. Finally, the fault-tolerant nature of a highly virtualized environment could raise questions about the level of redundancy required in the physical infrastructure. These particular effects of virtualization are discussed and possible solutions or methods for dealing with them are offered.
WP-157 v3
Eco-mode: Benefits and Risks of Energy-saving Modes of UPS Operation
Many newer UPS systems have an energy-saving operating mode known as “eco-mode” or by some other descriptor. Nevertheless, surveys show that virtually no data centers actually use this mode, because of the known or anticipated side-effects. Unfortunately, the marketing materials for these operating modes do not adequately explain the cost / benefit tradeoffs. This paper shows that eco-mode provides a reduction of approximately 2% in data center energy consumption and explains the various limitations and concerns that arise from eco-mode use. Situations where these operating modes are recommended and contra-indicated are also described.
WP-200 v0
Impact of Leading Power Factor on Data Center Generator Systems
IT devices may exhibit electrical input current with a characteristic called “leading power factor”. This situation may cause back-up generators to become unstable and shut down. Furthermore, a data center that is operating correctly for a long time may suddenly develop a problem as the IT load changes over time, or during an unusual event. This means that it is important to understand the margin of safety and correct for this condition before it happens. This paper explains the problem, why and how it occurs, and how to detect and correct it.
WP-61 v0
Electrical Distribution Equipment in Data Center Environments
IT professionals who are not familiar with the concepts, terminology, and equipment used in electrical distribution, can benefit from understanding the names and purposes of equipment that support the data center, as well as the rest of the building in which the data center is located. This paper explains electrical distribution terms and equipment types and is intended to provide IT professionals with useful vocabulary and frame of reference.
WP-194 v0
Arc Flash Considerations for Data Center IT Space
Do IT administrators violate arc flash requirements when they turn off or reset a branch circuit breaker? What about swapping out a rack power strip? Most data center operators are familiar with fire safety and shock hazard protection, but are less familiar with arc flash safety. Three IT trends have increased the severity of a potential arc flash in the IT space; higher data center capacities, higher rack densities, and higher efficiency designs. This paper discusses these three trends in the context of arc flash safety within the IT space. Arc flash is explained, potential areas of concern in the IT space are identified, and compliance with associated regulations is discussed.
WP-43 v3
Dynamic Power Variations in Data Centers and Network Rooms
The power requirement required by data centers and network rooms varies on a minute by minute basis depending on the computational load. This magnitude of this variation has grown and continues to grow dramatically with the deployment of power management technologies in servers and communication equipment. This variation gives rise to new problems relating to availability and management.
WP-92 v2
Comparison of Static and Rotary UPS
Much confusion exists among data center professionals when deciding whether to deploy static or rotary Uninterruptible Power Supplies (UPS) in their data centers. This paper defines both static and rotary UPS architectures, points out similarities and differences, and analyzes the advantages and disadvantages of each in data center environments.
WP-29 v7
Rack Powering Options for High Density
Alternatives for providing electrical power to high density racks in Data Centers and Network Rooms are explained and compared. Issues addressed include quantity of feeds, single-phase vs. three-phase, number and location of circuit breakers, overload, selection of plug types, selection of voltage, redundancy, and loss of redundancy. The need for the rack power system to adapt to changing requirements is identified and quantified. Guidelines are defined for rack power systems that can reliably deliver power to high density loads while adapting to changing needs.
WP-90 v1
Essential Standby Generator System Requirements for Next Generation Data Centers
Effective standby generator system installations must address the known problems and challenges relating to current and past designs. This paper presents a categorized and prioritized overview of generator system challenges and the requirements needed to overcome them.
WP-48 v1
Comparing Availability of Various Rack Power Redundancy Configurations
Transfer switches and dual-path power distribution to IT equipment are used to enhance the availability of computing systems. Statistical availability analysis techniques suggest large differences in availability are expected between the various methods commonly employed. This paper examines various electrical architectures for redundancy that are implemented in today’s mission-critical environments. The availability analyses of these various scenarios are then performed and the results are presented. The analysis identifies which approach provides the best overall performance, and how alternatives compare in performance and value.
WP-120 v2
Guidelines for Specification of Data Center Power Density
Conventional methods for specifying data center density are ambiguous and misleading. Describing data center density using Watts / ft2 or Watts / m2 is not sufficient to determine power or cooling compatibility with high density computing loads like blade servers. Historically there is no clear standard way of specifying data centers to achieve predictable behavior with high density loads. An appropriate specification for data center density should assure compatibility with anticipated high density loads, provide unambiguous instruction for design and installation of power and cooling equipment, prevent oversizing, and maximize electrical efficiency. This paper describes the science and practical application of an improved method for the specification of power and cooling infrastructure for data centers.
WP-27 v3
Efficiency and Other Benefits of 208 Volt Over 120 Volt Input for IT Equipment
Decisions made regarding the distribution of 208V or 120V power to IT equipment can significantly impact overall efficiency of the data center. This paper explores the voltage connection options of 208 volt (V) and 120V for servers in North America and considers the efficiency implications of these choices. This same discussion applies to the use of 200V vs. 100V in Japan.
WP-98 v0
The Role of Isolation Transformers in Data Center UPS Systems
Most modern UPS systems do not include the internal transformers that were present in earlier designs. This evolution has increased efficiency while decreasing the weight, size, and raw materials consumption of UPS systems. In the new transformerless UPS designs, the transformers are optional and can be placed in the best location to achieve a required purpose. In older designs, transformers were typically installed in permanent positions where they provided no benefit, reduced system efficiency, or were not optimally located. This paper considers the function of transformers in UPS systems, when and how transformers should be used, and how the absence of internal transformers in newer UPS designs frequently improves data center design and performance.
WP-63 v6
AC vs DC Power Distribution for Data Centers
DC power distribution has been proposed as an alternative to AC power distribution in data centers, but misinformation and conflicting claims have confused the discussion. A detailed analysis and model show that many of the benefits commonly stated for DC distribution are unfounded or exaggerated. This paper explains why high efficiency AC will likely emerge as the dominant choice for data center power distribution.
WP-128 v2
High-Efficiency AC Power Distribution for Green Data Centers
The use of 240 volt power distribution for data centers saves floor space, simplifies power cabling, saves capital cost, reduces weight, and increases electrical efficiency. This paper describes the various con-figurations for this distribution architecture and quantifies the benefits for the optimal configuration. Note: The methods in this paper only apply in North America and are for problems that are unique to North America.
WP-28 v1
Rack Powering Options for High Density in 230VAC Countries
Alternatives for providing electrical power to high density racks in data centers and network rooms are explained and compared. Issues addressed include quantity of feeds, single-phase vs. three-phase, number and location of circuit breakers, overload, selection of connector types, selection of voltage, redundancy, and loss of redundancy. The need for the rack power system to adapt to changing requirements is identified and quantified. Guidelines are defined for rack power systems that can reliably deliver power to high density loads while adapting to changing needs.
WP-18 v1
The Seven Types of Power Problems
Many of the mysteries of equipment failure, downtime, software and data corruption, are often the result of a problematic supply of power. There is also a common problem with describing power problems in a standard way. This white paper will describe the most common types of power disturbances, what can cause them, what they can do to your critical equipment, and how to safeguard your equipment, using the IEEE standards for describing power quality problems.
WP-108 v3
Making Large UPS Systems More Efficient
As energy resources become scarcer and more expensive, electrical efficiency is becoming a more important performance factor in the specification and selection of large UPS systems. There are three subtle but significant factors that can materially affect a company’s cost of operating a UPS system and particularly the electrical bill. Unfortunately, the people who specify systems often fail to recognize these factors, which leads to increased costs to the owner because operational efficiencies are not correctly considered. This paper discusses the common errors and misunderstandings in evaluating UPS efficiency. UPS efficiency curves are explained, compared, and their cost implications quantified.
WP-73 v1
Reducing the Hidden Costs Associated with Upgrades of Data Center Power Capacity
Scaling the power capacity of legacy UPS systems leads to hidden costs that may outweigh the very benefit that scalability intends to provide. A scalable UPS system provides a significant benefit to the Total Cost of Ownership (TCO) of data center and network room physical infrastructure. This paper describes the drawbacks of scaling legacy UPS systems and how scalable rack-based systems address these drawbacks. The cost factors of both methods are described, quantified and compared.
WP-109 v1
Reliability Analysis of the APC Symmetra MW Power System
This paper is a quantitaive reliability analysis of the APC Symmetra MW UPS performed by MTechnology, Inc. (MTech). In contrast to common MTBF calculations based on summing component failure rates, this study used techniques of Probabilistic Risk Assessment (PRA) to calculate the likelihood of over 680, 000 potential failure modes. The mathematical method accounts for uncertainty in failure rates and component performance, and provides detailed guidance as to the contribution of each system component to the overall risk of failure. The study included an exhaustive analysis of the system’s architecture, component selection, control system, manufacturing practices, and response to internal and external faults. The study also included a detailed review of APC’s delta conversion online topology.
WP-111 v2
Reliability Analysis of the APC InfraStruXure Power System
The APC InfraStruXure product line offers an alternative architecture to the central UPS. MTechnology, Inc. used the techniques of Probabilistic Risk Assessment (PRA) to evaluate the reliability of the 40 kW InfraStruXure UPS and PDU with static bypass. The calculations considered the performance of the InfraStruXure in both ideal and real-world conditions. The study also compared the performance of the InfraStruXure architecture to that of a central UPS serving a hypothetical 500 kW critical load in a data center. The results showed that the InfraStruXure architecture was significantly less likely to suffer failure of all loads in the data center, and slightly less likely to experience failure in any one piece of IT equipment. This paper summarizes the key findings of MTechnology's quantitative risk assessment and discusses their implications for facility managers and designers.
WP-52 v1
Four Steps to Determine When a Standby Generator is Needed for Small Data Centers
Small data centers and network rooms vary dramatically in regard to the amount of UPS runtime commonly deployed. This paper describes a rational framework for establishing backup time requirements. Tradeoffs between supplemental UPS batteries and standby generators are discussed, including a total cost of ownership (TCO) analysis to help identify which solution makes the most economic sense. The analysis illustrates that the runtime at which generators become more cost effective than batteries varies dramatically with kW and ranges from approximately 20 minutes to over 10 hours.
WP-62 v1
Powering Single-Corded Equipment in a Dual Path Environment
The use of dual power path architecture in combination with IT equipment with dual power supplies and power cords is an industry best-practice. In facilities using this approach there are inevitably some IT devices which have only a single power cord. There are a number of options for integrating single-corded devices into a high availability dual path data center. This paper explains the differences between the various options and provides a guide to selecting the appropriate approach.
WP-65 v2
Comparing Data Center Batteries, Flywheels, and Ultracapacitors
Most data center professionals choose lead-acid batteries as their preferred method of energy storage. However, alternatives to lead-acid batteries are attracting more attention as raw material and energy costs continue to increase and as governments become more vigilant regarding environmental and waste disposal issues. This paper compares several popular classes of batteries, compares batteries to both flywheels and ultracapacitors, and briefly discusses fuel cells.
WP-8 v2
Inter-system Ground Noise: Causes and Effects
Many power-related problems are the result of Inter-System Ground Noise. This problem cannot be corrected using typical AC-only power protection equipment. The cause and solution of Inter-System Ground Noise problems are described.
WP-22 v5
Understanding EPO and its Downtime Risks
An Emergency Power Off (EPO) system is a control mechanism, formally known as a "disconnecting means." It is intended to power down a single piece of electronic equipment or an entire installation from a single point. EPO is employed in many applications such as industrial processes and information technology (IT). This white paper describes the advantages and disadvantages of EPO for protecting data centers and small IT equipment rooms containing uninterruptible power supply (UPS) systems. Various codes and standards that require EPO are discussed. Recommended practices are suggested for the use of EPO with UPS systems.
WP-69 v1
Power and Cooling for VoIP and IP Telephony Applications
Voice Over IP (VoIP) deployments can cause unexpected or unplanned power and cooling requirements in wiring closets and wiring rooms. Most wiring closets do not have uninterruptible power available, and they do not provide the ventilation or cooling required to prevent equipment overheating. Understanding the unique cooling and powering needs of VoIP equipment allows planning for a successful and cost effective VoIP deployment. This paper explains how to plan for VoIP power and cooling needs, and describes simple, fast, reliable, and cost effective strategies for upgrading old facilities and building new facilities.
WP-1 v7
The different types of UPS systems
There is much confusion in the marketplace about the different types of UPS systems and their characteristics. Each of these UPS types is defined, practical applications of each are discussed, and advantages and disadvantages are listed. With this information, an educated decision can be made as to the appropriate UPS topology for a given need.
WP-38 v1
Harmonic Currents in the Data Center: A Case Study
This document provides an overview of how problems related to harmonic neutral currents are mitigated by load diversity, with specific focus on Information Technology data center environments. Detailed measurements of an actual operating data center are presented. This case study illustrates the way that load diversity mitigates harmonic current levels, lowers shared neutral current in multi-wire feeders and branch circuits, and improves total circuit power factor.
WP-36 v1
Data Center VRLA Battery End-of-Life Recycling Procedures
Contrary to popular belief, the recycling of lead-acid batteries, which are the most common batteries found in data centers, is one of the most successful recycling systems that the world has ever seen. Reputable battery manufacturers, suppliers, and recycling companies have teamed up to establish a mature and highly efficient lead-acid battery recycling process. This paper reviews battery end-of-life options and describes how a reputable vendor can greatly facilitate the safe disposal and recycling of VRLA lead-acid batteries.
WP-15 v1
Watts and Volt-Amps: Powerful Confusion
This note helps explain the differences between Watts and VA and explains how the terms are correctly and incorrectly used in specifying power protection equipment.
WP-3 v1
Calculating Total Power Requirements for Data Centers
Part of data center planning and design is to align the power and cooling requirements of the IT equipment with the capacity of infrastructure equipment to provide it. This paper presents methods for calculating power and cooling requirements and provides guidelines for determining the total electrical power capacity needed to support the data center, including IT equipment, cooling equipment, lighting, and power backup.
WP-96 v1
A Hidden Reliability Threat in UPS Static Bypass Switches
IT managers will be surprised to learn that some medium and high power UPS systems on the market today (rated 50 kW and higher) use undersized static bypass switches despite their negative implications. By using a contactor or a circuit breaker in parallel with SCRs, these static bypass switches are able use smaller, less expensive SCRs that are rated to carry less than full load current continuously. This paper shows that the availability of the UPS system is compromised when undersized static bypass switches are employed in the system. The advantages of fully rated static bypass switches are discussed.
WP-79 v1
Technical comparison of On-line vs. Line-interactive UPS designs
UPS systems below 5000VA are available in two basic designs: line-interactive or double-conversion on-line. This paper describes the advantages and disadvantages of each topology and addresses some common misconceptions about real-world application requirements.
WP-21 v1
Neutral Wire Facts and Mythology
This Technical Note discusses many common misunderstandings about the function of the neutral wire and its relation to power problems. The subjects of dedicated lines, phase reversal, isolation transformers, and grounding are addressed. Various myths are described and criticized.
WP-60 v2
Avoiding AC Capacitor Failures in Large UPS Systems
Most AC power capacitor failures experienced in large UPS systems are avoidable. Capacitor failures can give rise to UPS failure and can in some cases cause critical load drops on stand-alone and paralleled systems. AC capacitor failures have historically been ascribed to unavoidable random failure or supplier defect. However, recent advances in the science of capacitor reliability analysis show that capacitor failures can be controlled by system design. This paper explains AC capacitor failure mechanisms and demonstrates how UPS designers and specifiers can avoid most common AC capacitor failures and the associated consequences.
WP-9 v2
Common Mode Susceptibility of Computers
This white paper examines and challenges the claims made in literature regarding the alleged high susceptibility of computers to common mode noise.
WP-32 v7
Battery Technology for Data Centers and Network Rooms: Environmental Regulations
Some lead-acid batteries located in data centers are subject to government environmental compliance regulations. While most commercial battery back-up systems fall below required reporting levels, very large UPS and DC plant batteries may have to comply. Failure to comply can result in costly penalties. Environmental compliance regulations focus on the amount of sulfuric acid and lead in a given location. This paper offers a high level summary of the regulations and provides a list of environmental compliance information resources.
WP-75 v3
Comparing UPS System Design Configurations
There are five principle UPS system design configurations that distribute power from the utility source of a building to the critical loads of a data center. The selection of the appropriate configuration or combination thereof for a particular application is determined by the availability needs, risk tolerance, types of loads in the data center, budgets, and existing infrastructure. This paper will focus on these five configurations; the advantages and disadvantages of each are discussed. The impact on availability is addressed for each configuration and guidelines are provided for choosing the appropriate design.
WP-85 v1
Data Line Transient Protection
Electrical transients (surges) on data lines can destroy computing equipment both in the business and home office environments. Many users appreciate the risk of power surges but overlook data line surges. This white paper explains how transients are created, how they can have devastating effects on electrical equipment, and how surge suppression devices work to help protect against them.
WP-35 v4
Battery Technology for Data Centers and Network Rooms: Lifecycle Costs
The lifecycle cost of different UPS battery technologies is compared. The costs associated with the purchase of batteries, the infrastructure costs, and the costs associated with inflexibility to meet changing requirements are discussed and quantified.
WP-33 v5
Battery Technology for Data Centers and Network Rooms: Site Planning
The choice of UPS battery technology directly impacts site requirements and the costs for protecting information technology and network environments. This paper will discuss how battery technologies impact site requirements.
WP-24 v3
Effect of UPS on System Availability
This white paper explains how system availability and uptime are affected by AC power outages and provides quantitative data regarding uptime in real-world environments, including the effect of UPS on uptime.
WP-17 v1
Understanding Power Factor, Crest Factor, and Surge Factor
This white paper explains the technical terms of power factor, crest factor, and surge factor. The use of these terms in specifying UPS is explained.
WP-20 v1
The Different Types of AC Power Connectors in North America
A confusing array of AC power plugs and receptacles exist to deliver power to various electronic loads. This white paper describes the different types of connectors used to power computer equipment in North America. An illustration guide is provided in the appendix to help identify the various connectors by appearance and size.
WP-34 v3
Battery Technology for Data Centers and Network Rooms: Ventilation of Lead-Acid Batteries
Lead-acid batteries are the most widely used method of energy reserve. Ventilation systems must address health and safety as well as performance of the battery and other equipment in a room. Valve regulated lead acid (VRLA) batteries and modular battery cartridges (MBC) do not require special battery rooms and are suitable for use in an office environment. Air changes designed for human occupancy normally exceed the requirements for VRLA and MBC ventilation. Vented (flooded) batteries, which release hydrogen gas continuously, require a dedicated battery room with ventilation separate from the rest of the building. This paper summarizes some of the factors and U.S. codes to consider when selecting and sizing a ventilation system for a facility in which stationary batteries are installed.
WP-23 v1
Reliability Models for Electric Power Systems
This white paper explains the sources of downtime in electric power systems and provides an explanation for site-to-site variations in power availability. The factors affecting power quality from generation to the utilization point are summarized. There is a qualitative description of a model, which can be combined with data to provide a method for estimating down time based on site-related factors.
WP-93 v1
Fundamental Principles of Generators for Information Technology
Every Information Technology professional who is responsible for the operation of computing equipment needs to ensure their data center or network room is prepared for extended utility power outages. Understanding the basic functions and concepts of standby generator systems helps provide a solid foundation allowing IT professionals to successfully specify, install, and operate critical facilities. This paper is an introduction to standby generators and subsystems that power a facility’s critical electrical loads when the utility cannot.
WP-113 v2
Electrical Efficiency Modeling for Data Centers
Conventional models for estimating electrical efficiency of data centers are grossly inaccurate for real-world installations. Estimates of electrical losses are typically made by summing the inefficiencies of various electrical devices, such as power and cooling equipment. This paper shows that the values commonly used for estimating equipment inefficiency are quite inaccurate. A simple, more accurate efficiency model is described that provides a rational basis to identify and quantify waste in power and cooling equipment.
WP-31 v8
Battery Technology for Data Centers and Network Rooms: U.S. Fire Safety Codes Related to Lead Acid Batteries
Fire safety regulations and their application to UPS battery installations are reviewed. In some cases, fire codes do not clearly recognize improvements in battery safety resulting from changing battery technology. Valve Regulated Lead Acid (VRLA) batteries are frequently deployed within data centers and network rooms without the need for the elaborate safety systems that are required for Vented (Flooded) Lead Acid batteries. Proper interpretation of the fire codes is essential in the design and implementation of data centers and network rooms.
WP-39 v2
Battery Technology for Data Centers and Network Rooms: VRLA Reliability and Safety
The Valve Regulated lead-Acid (VRLA) battery is the predominant choice for small and medium-sized Uninterruptible Power Supply (UPS) energy storage. This white paper explores how the technology affects overall battery life and system reliability. It will examine the expected performance, life cycle factors, and failure mechanisms of VRLA batteries.
WP-30 v12
Battery Technology for Data Centers and Network Rooms: Lead-Acid Battery Options
The lead-acid battery is the predominant choice for Uninterruptible Power Supply (UPS) energy storage. Over 10 million UPSs are presently installed utilizing Flooded, Valve Regulated Lead Acid (VRLA), and High Density Modular Battery Cartridges (HDBCMBC) systems. This paper discusses the advantages and disadvantages of these three battery technologies.
WP-87 v2
Grounding and the Use of the Signal Reference Grid in Data Centers
Signal reference grids are automatically specified and installed in data centers despite the fact that they are no longer needed by modern IT equipment. Even when installed, they are typically used incorrectly. This paper explains the origins of the signal reference grid, the operating principles and limitations, and why they no longer are needed.