Editing 19-inch rack (section)

===Structural support===
Rack-mountable equipment is traditionally mounted by bolting or clipping its front panel to the rack. Within the IT industry, it is common for network/communications equipment to have multiple mounting positions, including tabletop and wall mounting, so rack-mountable equipment will often feature L-brackets that must be screwed or bolted to the equipment prior to mounting in a 19-inch rack. With the prevalence of [[#Related standards|23-inch racks]] in the Telecoms industry, the same practice is also common, but with equipment having 19-inch and 23-inch brackets available, enabling them to be mounted in existing racks.

A key structural weakness of front-mounted support is the bending stress placed on the mounting brackets of the equipment, and the rack itself. As a result, 4-post racks have become common, featuring a mirrored pair of rear mounting posts. Since the spacing between the front and rear mounting posts may differ between rack vendors and/or the configuration of the rack (some racks may incorporate front and rear rails that may be moved forwards and backward, e.g. APC SX-range racks), it is common for equipment that features 4-post mounting brackets to have an adjustable rear bracket.

Servers and deep pieces of equipment are often mounted using rails that are bolted to the front and rear posts (as above, it is common for such rails to have an adjustable depth), allowing the equipment to be supported by four posts, while also enabling it to be easily installed and removed.

Although there is no standard for the depth of equipment, nor specifying the outer width and depth of the rack enclosure itself (incorporating the structure, doors and panels that contain the mounting rails), there is a tendency for 4-post racks to be {{convert|600|mm|in|2|abbr=on}} or {{convert|800|mm|in|2|abbr=on}} wide, and for them to be {{convert|600|mm|in|2|abbr=on}}, {{convert|800|mm|in|2|abbr=on}} or {{convert|1010|mm|in|2|abbr=on}} deep. This of course varies by manufacturer, the design of the rack and its purpose, but through common constraining factors (such as raised-floor tile dimensions), these dimensions have become quite common. The extra width and depth enables cabling to be routed with ease (also helping to maintain the minimum bend radius for fiber and copper cables) and deeper equipment to be utilized. A common feature in IT racks is mounting positions for ''zero-U'' accessories, such as [[power distribution unit]]s (PDUs) and vertical cable managers and ducts, that utilize the space between the rear rails and the side of the rack enclosure.

The strength required of the mounting posts means they are invariably not merely flat strips but actually a wider folded strip arranged around the corner of the rack. The posts are usually made of [[steel]] of around 2&nbsp;mm thickness (the official standard recommends a minimum of 1.9&nbsp;mm), or of slightly thicker [[aluminum]].

Racks, especially two-post racks, are often secured to the floor or adjacent building structure so as not to fall over. This is usually required by local building codes in [[Earthquake|seismic zones]]. According to [[Telcordia Technologies]] Generic Requirements document GR-63-CORE, during an earthquake, telecommunications equipment is subjected to motions that can over-stress equipment framework, circuit boards, and connectors. The amount of motion and resulting stress depends on the structural characteristics of the building and framework in which the equipment is contained and the severity of the earthquake. Seismic racks rated according to  [https://telecom-info.njdepot.ericsson.net/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=GR-63& GR-63], ''NEBS Requirements: Physical Protection,'' are available,<ref>[https://telecom-info.njdepot.ericsson.net/ido/AUX/GR_63_TOC.i03.pdf Telcordia GR-63-CORE, NEBS Requirements: Physical Protection]</ref> with Zone 4 representing the most demanding environment.<ref>{{cite web|title=Telcordia GR-1502-CORE, Central Office/Network Environment Detail Engineering Generic Requirements |url=https://telecom-info.njdepot.ericsson.net/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=GR-1502& |archive-url=https://web.archive.org/web/20110716204652/https://telecom-info.njdepot.ericsson.net/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=GR-1502& |archive-date=2011-07-16 |url-status=live |access-date=2009-07-27 }}</ref><ref>{{Cite web |url=http://www.hoffmanonline.com/stream_document.aspx?rRID=16186&pRID=16185 |title=Seismic Enclosures Provide an Extra Measure of Protection |access-date=2007-10-29 |archive-date=2009-01-13 |archive-url=https://web.archive.org/web/20090113154540/http://www.hoffmanonline.com/stream_document.aspx?rRID=16186&pRID=16185 |url-status=dead }}</ref>

[https://telecom-info.njdepot.ericsson.net/site-cgi/ido/docs.cgi?ID=SEARCH&DOCUMENT=GR-3108& GR-3108], ''Generic Requirements for Network Equipment in the Outside Plant (OSP),'' specifies the usable opening of seismic-compliant 19-inch racks.