What Does EIA Stand For?
EIA is an initialization for the Electronic Industries Alliance. This alliance represented a group of trade associations for electronic manufacturers in the United States before its dissolution in 2011. EIA standards are still maintained by former sectors of the alliance, with differentiating naming conventions based on the industry and respective sectors.
What is EIA-310-D?
EIA-310-D is the original document issued by the Electronic Industries Association – renamed the Electronic Alliance in 1997 – written to standardize varying features of 19” rack cabinets. The document outlines specific guidelines for several important terms often used in the server rack industry. Terms such as Rack Units (RU or U), vertical hole spacing, horizontal hole spacing, rack opening, and front panel width.
Below is a short description of each term outlined by the document and the parameters in which they lie.
Vertical Hole Spacing
Vertical hole spacing is defined as a repeating pattern of holes within one Rack Unit of 1.75”. The whole spacing alternates at 1/2” – 5/8” – 5/8” and then repeats. The “U” space starts and stops in the middle of the 1/2” holes.
Horizontal spacing of vertical rows is specified by EIA-310 at 19 5/16” (18.312) (465.1 mm). This dimension is not universal to all racks which in turn causes problems during installation of equipment. Most manufactures, however, use equipment mounting slots instead of holes to allow for variations in this dimension.
The opening in the rack is specified at a minimum of 17.72” (450 mm) 2-Post or telco relay racks typically err larger than this, as do many other racks with threaded holes. Square hole racks tend to be close to the minimum opening specification.
Front Panel Width
The front panel width is the only dimension on a 19” rack that actually measures 19”.
EIA standards are not mandated by any governing bodies, meaning compliance is not enforced. Manufactures are at liberty to choose whether or not they want to build cabinets in adherence with the document. Most manufactures will abide by the standards laid out by EIA to maintain continuity with the antiquated market standards.