What does 1U, 2U or 3U mean?

Many rack-mounted power systems are specified as being 1U, 2U, 3U, etc. What does this mean? For electronic equipment racks (e.g., 19 or 23 inches wide), the term 1U is used to define one rack unit of height.

1U equals 1.75-inches (44.45mm) of rack height. Therefore, a 2U rack mount height would be 2 x 1.75", which equals 3.5-inches high. A 3U height would be 3 x 1.75" = 5.25-inches.

It should be noted that the 1U, 2U, 3U, etc., heights are maximum dimensions. In order to allow for mechanical tolerances and to provide some space between panels, typically, for each 1U of height manufacturers may deduct about 0.03" (see Photo #1). For example, a 2U panel, which has a nominal height of 3.50" may be only 3.44" high [3.50" – (2 x 0.03") = 3.44"].

Individual power supplies are sometimes mounted within rack-mounted enclosures that require integral power. In these cases, the power supply needs to be a bit shorter than the equipment’s overall height to allow for the top and bottom covers. So a 1U high enclosure-mountable power supply needs to be shorter than 1.75-inches; a 2U enclosure-mountable supply needs to be shorter than 3.5-inches, and so forth (see Photo #2).

Examples

Photo #1: This 19" rack-mountable power system can hold up to 3 plug-in, hot-swap and redundant power supplies. The enclosure with mounting ears is 1.72" high (= 1.75" minus 0.03") and is therefore considered 1U high.

Photo #2: This 1000-watt switch-mode power supply is 3.25” high and, therefore, can be mounted in a 2U rack-mountable enclosure, which can vary between 3.44" to 3.50" high.

Here are a couple of handy conversion factors: 1 inch = 25.4 millimeters (mm), 1 mm = 0.03937 inch.

Server Rack Basics

What is a server rack?

Server racks are open frames or cabinets designed for mounting, organizing and securing EIA-standard 19-inch width rack-mount IT and A/V equipment such as servers, routers, hubs, switches and audio/video components,regardless of the manufacturer. They also provide cable

management and enable optimized airflow for increased operational efficiency and prolonged equipment life.

where are server racks used?

• Data centers Industrial/factory

• Server roomsEdge of network locations Earthquake zone networks A/V & digital signage installations

•

Quiet network Locations

• Classrooms

Network closets

Top Server Rack Features

Provide organization and security for critical equipment Server racks have sturdy steel frames and locking cabinets to secure and organize up to 3,000 lbs. of 19-inch rack equipment. They provide safe homes for servers, storage, network hardware and all the indispensable devices that keep your network efficient and productive.

Deliver efficient cooling

 Most network racks feature front-to-rear airflow that supports efficient hot-

aisle/cold-aisle configurations and exceed server manufacturer requirements to keep equipment operating reliably. Roof and

panel fans are also available to optimize cooling efficiency.

Support diverse applications

Many server rack heights, widths, depths and other variations are available, with a wide range of configuration options so support any application.

Makes your job easier

Most server racks have been designed to optimize installation and maintenance, and that philosophy shows in the details that make routine tasks quicker and easier, adding up to big benefits over the workday.

Features like quick-adjust mounting rails, modular side panels and toolless mounting slots for vertical PDUs and cable managers facilitate installation and configuration. Seamless compatibility with all EIA-standard 19-inch rack equipment ensures trouble-free setup.

  Types of Server Racks

premium-grade floor and wall mount server racks and cabinets enclosures-cabinet organize and secure IT equipment wherever it is located, from high-density data centers to the tightest of spaces at the edge of your network.

Compatible designs, tool-less mounting and an extensive line of rack accessories mean easier planning, faster deployments and more efficient maintenance.

A rack unit (abbreviated U or RU) is a unit of measure defined as 1+³⁄₄ inches (44.45 mm). It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby the height of the frame or equipment is expressed as multiples of rack units. For example, a typical full-size rack cage is 42U high, while equipment is typically 1U, 2U, 3U, or 4U high.

The rack unit size is based on a standard rack specification as defined in EIA-310. The Eurocard specifies a standard rack unit as the unit of height; it also defines a similar unit, horizontal pitch (HP), used to measure the width of rack-mounted equipment. The standard was adopted worldwide as IEC 60297 Mechanical structures for electronic equipment – Dimensions of mechanical structures of the 482.6 mm (19 in) series, and defines the sizes for rack, subrack (a shelf-like chassis in which cards can be inserted), enclosures-cabinetand the pitch of printed circuit boards/cards providing physical compatibility of technological equipment, typically in telecommunications.

While a rack unit is defined as 1+³⁄₄ inches (44.45 mm), a front panel or filler panel in a rack is not an exact multiple of this height. To allow space between adjacent rack-mounted components, a panel is ¹⁄₃₂ inches (0.03125 in or 0.794 mm) less in height than the full number of rack units would imply. Thus, a 1U front panel would be 1²³⁄₃₂ inches (1.71875 in or 43.66 mm) tall. If n is number of rack units, the ideal formula for panel height is h = (1.75n − 0.031) for calculating in inches, and h = (44.45n − 0.794) for calculating in millimetres. Manufacturing allows for dimensions with less precision.

An electrical enclosure is a cabinet for electrical or electronic equipment to mount switches, knobs and displays and to prevent electrical shock to equipment users and protect the contents from the environment. The enclosure is the only part of the equipment which is seen by users. It may be designed not only for its utilitarian requirements, but also to be pleasing to the eye. Regulations may dictate the features and performance of enclosures for electrical equipment in hazardous areas, such as petrochemical plants or coal mines. Electronic packaging may place many demands on an enclosure for heat dissipation, radio frequency interference and electrostatic discharge protection, as well as functional, esthetic and commercial constraints.The 42 Extra cables, improved

airflow

Standards:

nternationally, IEC 60529 classifies the IP Codes (ingress protection rating) of enclosures.

In the United States, the National Electrical Manufacturers Association (NEMA) publishes NEMA enclosure type standards for the performance of various classes of electrical enclosures. The NEMA standards cover corrosion resistance, ability to protect from rain and submersion, etc.

Materials:

Electrical enclosures are usually made from rigid plastics, or metals such as steel, stainless steel, or aluminum. Steel cabinets may be painted or galvanized. Mass-produced equipment will generally have a customized enclosure, but standardized enclosures are made for custom-built or small production runs of equipment. For plastic enclosures ABS is used for indoor applications not in harsh environments. Polycarbonate, glass-reinforced, and fiberglass boxes are used where stronger cabinets are required, and may additionally have a gasket to exclude dust and moisture.

Metal cabinets may meet the conductivity requirements for electrical safety bonding and shielding of enclosed equipment from electromagnetic interference. Non-metallic enclosures may require additional installation steps to ensure metallic conduit systems are properly bonded.

(PLC) installed in an electrical enclosure

stainless steel and carbon steel

Carbon steel and stainless steel are both used for enclosure construction due to their high durability and corrosion resistance. These materials are also moisture resistant and chemical resistant. They are the strongest of the construction options. Carbon steel can be hot or cold rolled.

Hot rolled carbon steel is used for stamping and moderate forming applications. Cold rolled sheet is produced from low carbon steel and then cold reduced to a certain thickness and can meet ASTM A366 and ASTM A611 requirements。

Stainless steel enclosures are suited for medical, pharma, and food industry applications since they are bacterial and fungal resistant due to their non-porous quality Stainless steel enclosures may be specified to permit wash-down cleaning in, for example, food manufacturing areas.

Aluminum

Aluminum is chosen because of its light weight, relative strength, low cost, and corrosion resistance. It performs well in harsh environments and it is sturdy, capable of withstanding high

impact with a high malleable strength. Aluminum also acts as a shield against electromagnetic interference.

Polycarbonate

Polycarbonate used for electrical enclosures is strong but light, non-conductive and non-magnetic. It is also resistant to corrosion and some acidic environments; however, it is sensitive to abrasive cleaners. Polycarbonate is the easiest material to modify.

Fiberglass

Fiberglass enclosures resist chemicals in corrosive applications. The material can be used over all indoor and outdoor temperature ranges. Fiberglass can be installed in environments that are constantly wet.

Terminology

Enclosures for some purposes have partially punched openings (knockouts) which can be removed to accommodate cables, connectors, or conduits. Where they are small and primarily intended to conceal electrical junctions from sight, or protect them from tampering, they are also known as junction boxes, street cabinets or technically as serving area interface.

Telecommunications

Telecommunication enclosures are fully assembled or modular field-assembled transportable structures capable of housing an electronic communications system. These enclosures provide a controlled internal environment for the communications equipment and occasional craftspeople. The enclosures are designed with locks, security, and alarms to discourage access by unauthorized persons. Enclosures can be provided with a decorative facade to comply with local building requirements.

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