EIA stands for the Electronic Industries Alliance. The EIA standards direct component marking, data modeling, color coding and packaging materials. EIA-310 is a specification for the “standard rack”. This specification standardizes key features of 19″ racks, such as the rack unit, vertical hole spacing, horizontal hole spacing, rack opening and front panel width. The latest revision is EIA-310-D.
A rack unit is a unit of measure defined as 1.75 inches. It is used as a unit of measurement for the overall height of 19 inches rack frames. For example, server system that requires 1U rack space, or has a 1U rack chassis form factor, means the server system occupies 1.75” of vertical space within the networking cabinet or rack. A server system with a 2U rack chassis form factor will occupy 3.5” of vertical space.
Networking cabinets or racks that follows the EIA-310 standard also uses 1.75” as a rack unit. Meaning, a 6U cabinet or rack will be able to mount six 1U server systems, or three 2U server systems.
Front Panel Width
On a 19” rack, the 19” dimension measures the front flange width of the mounting equipment:
The opening in the rack is specified at a minimum of 450 mm (17.72”). 2-Post racks and many other racks with threaded holes are often larger. Square hole racks tend to be close to the minimum opening specification.
The horizontal spacing of the vertical rows of holes is specified by EIA-310 at 18 & 5/16″, or 18.312”, which equates to 465.1 mm.
The vertical spacing is defined as a repeating pattern of holes 0.625” apart within one rack unit of 1.75”. Within one unit, the second hole is in the middle of the rack unit, which the first and the third hole is 0.625” away from the second hole.
Referencing the photo below you will see 0.625” + 0.625” + 0.50” = 1.75”.
NavePoint cabinets and racks abides by the standards laid out by EIA to maintain continuity with the market offerings to ensure proper fit and function of most 19” chassis.
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