Audio-Video Equipment Racks (1)
Standard 19-inch Rack Basics

Equipment racks come in all shapes and sizes, and are as diverse as the equipment they carry. Yet there are a few basics about standard 19-inch rack enclosures that apply irrespective of brand, shape, and size. More in this guide to standard 19-inch racks.

Origins of Rack-Mounting

Equipment racks, also referred to as rack enclosures, are part of nearly every major home theater installation, with most advanced audio video installations making use of standard 19-inch racks.

Yet the origins of rack mounting dates to the days of industrialist George Westing-house way back in 1890.

Westinghouse had first designed 19-inch shelving to house relay gear used in his railroad industry. Eventually, early telephone companies also adopted this 19-inch width.

The 19-inch width for equipment racks still lives today. Eventually, it was the Electronic Industries Alliance (EIA) that finally standardized this 19-inch structure through its 310-D standard, first published in 1965. It defines a 1.75-inch (44.45mm) 'rackspace' height and 19-inch (482.6mm) width to make equipment interchangeable within common housings.

One may also come across other similar standards related to 19-inch rack systems. These include the 60297 standard series, set by the IEC (International Electrotechnical Commission), and the 41494 SC48D - set by the German Institute for Standardization or DIN (Deutsches Institut für Normung e.V.). Both standards deal with the dimensions of the mechanical structure of 19-inch racks and related sub-components.

Modern AV Equipment Racks

Rack mounting have evolved into a sophisticated system of enclosures covering various designs that are as diverse as the equipment they hold. This in view that though AV racks are governed by international standards, yet choosing the various rack components, including determining the rack's structural design, content, and covering, is left up to each individual manufacturer to accommodate end user requirements.

The Standard 19-inch Rack - Rack Anatomy

The front of each rack has two parallel, vertical metal mounting rails designed to hold equipment. These strips are each 0.625-inch wide and are separated by a gap of 17.75-inch, creating an overall rack width of 19-inch, hence the 19-inch standard.

These vertical mounting strips include regularly spaced holes - arranged vertically in repeating sets of three, with their centers separated by 0.5-inch, 0.625-inch, and 0.625-inch. This pattern repeats itself every 1.75-inch, forming the basic rack space called a rack unit, (denoted by RU or just U).

As a result, the vertical dimension of a standard 19-inch rack is often measured in the number of RU space compartments it can hold. On the other hand, equipment designed to fit these racks is conventionally described by the number of RUs it occupies.

Rack-mountable equipment is usually bolted onto the front vertical strips, while heavier equipment  would make use of a second pair of mounting strips located at the backside of the rack. Often, heavy equipment is also supported by horizontal rails that allow it to be slid out for maintenance.

With non-rackmountable gear - as is the case with most domestic home theater components, these horizontal rails can also be used to hold suitable shelves onto which to put your gear. It is important that these shelves include perforations to allow air to circulate freely between system components to avoid overheating.

Depth of equipment racks vary depending on the equipment to be mounted. Some slim-styled audio video equipment racks as used in home theater installations come with an overall depth of 22-inches. This still leaves more than enough internal space to hold most AV components.

Rack Height Considerations

As already pointed out, height of an EIA standard 19-inch equipment rack is often referred to in the number of RU or U spaces it can accommodate. With non-standard A/V equipment racks designed for home theater use, height is specified in inches. These non-standard racks - while still using 19-inch wide shelves - would normally indicate the number of equipment shelves that they can accommodate.

Working with EIA standard  19-inch racks would normally enable you to better customize the rack for your needs due to the vast range of compatible accessories available from major manufacturers.

Whatever rack system you adopt, keep in mind that the following may affect the required overall rack height: ventilation (fans, blowers, and thermostat controls), space for AC power distribution strips, power protection units such as surge suppressors, and cable management.

Rack Accessories

	One can find a never-ending-list of accessories for EIA 310-D standard racks. These range from cable managers, ventilation units, rackmount shelves and drawers, etc., available from various manufactures. These rack accessories are normally fully compatible with any 19-inch rack - irrespective of make.
This renders the standard 19-inch equipment rack, the most versatile rack solution since it is possible for the end user to come up with a customized rack system that best suit individual needs.

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