Overview and History
– Equipment designed for rack placement is described as rack-mount, rack-mount instrument, rack-mounted system, rack-mount chassis, subrack, rack cabinet, or rack-mountable.
– The height of electronic modules is standardized as multiples of 1.75 inches or one rack unit (U).
– The industry-standard rack cabinet is 42U tall, but 45U racks are also common.
– The term ‘relay rack’ originated in telephony and later used in railroad signaling.
– The 19-inch rack format with rack-units of 1.75 inches was established as a standard by AT&T in 1922.
Equipment Mounting
– Rack rails are used to mount equipment in a 19-inch rack.
– There are two-post and four-post rack configurations.
– Rack rails can be tapped with screw threads or use clearance holes and cage nuts.
– Square-hole racks allow for boltless mounting of equipment.
– L-brackets are used for tabletop and wall mounting of network/communications equipment.
Fastening
– Originally, mounting holes were tapped with a specific screw thread.
– Tapped-hole racks are still used for hardware that rarely changes.
– Clearance-hole racks have larger holes for freely inserting bolts and using cage nuts.
– Square-hole racks allow for easy boltless installation and removal of equipment.
– Cage nuts made for square-hole racks enable the use of older equipment meant for different rack types.
Structural Support
– Rack-mountable equipment is typically bolted or clipped to the front panel of the rack.
– Network/communications equipment may have multiple mounting positions, including tabletop and wall mounting.
– 4-post racks with rear mounting posts provide better structural support.
– Adjustable rear brackets are common for equipment with 4-post mounting brackets.
– Rails are used to mount servers and deep equipment, allowing for easy installation and removal.
Dimensions and Variations
– There is no standard for the depth of equipment or the outer width and depth of the rack enclosure.
– 4-post racks tend to be 600mm or 800mm wide and 600mm, 800mm, or 1,010mm deep.
– The 19-inch rack format is widely used in various industries.
– The Western Electric 23-inch standard is still used in legacy ILEC/CLEC facilities.
– The technology mounted within the 19-inch rack has changed considerably over time. Source: https://en.wikipedia.org/wiki/19_inch_rack
A 19-inch rack is a standardized frame or enclosure for mounting multiple electronic equipment modules. Each module has a front panel that is 19 inches (482.6 mm) wide. The 19 inch dimension includes the edges or ears that protrude from each side of the equipment, allowing the module to be fastened to the rack frame with screws or bolts. Common uses include computer servers, telecommunications equipment and networking hardware, audiovisual production gear, music production equipment, and scientific equipment.
