While electronics technologies have come and gone, mounting them in 19-in. racks is as popular as ever. There are various theories over the origin of the 19-in. rack, but Practical-Home-Theater-Guide.com says that George Westinghouse used 19-in racks in 1890s to mount railroad relays. Then, in the early 1900s, telephone companies designed their switches to fit in 19-in. racks.
In 1965, the Electronics Industry Association published EIA Standard 310, Cabinets, Racks, Panels, and Associated Equipment. The latest revision is EIA/ECA 310-E, which was published in December 2005. The standard is available from Global IHS.
Amazingly, 19-in. racks are still widely used. The biggest users of 19-in. racks are IT companies, which use them to mount IT equipment, such as servers and network switches. Test equipment companies are also big users of 19-in. racks. Many AMETEK Programmable Power power sources, such as the new Asterion AC/DC power source and the Sorensen XG Series of DC power supplies, are designed to be mounted in 19-in. racks. When properly used, they provide protection from harsh environmental conditions physical security, cooling, cable management, and mobility for test systems.
How to choose the right rack
When choosing a rack for your test system there are four major considerations: height, width, depth, and load rating:
Height. The height of the rack may be the most important consideration. Common heights for floor-standing racks and rack enclosures are 42U, 45U and 48U, with custom sizes up to 58U, where U is equal to 1.752 inches. Before selecting a height, consider all of the equipment that you'll want to mount in the rack and leave extra space for future expansion, if you can.
Width. Since the width of the rack’s mounting rails is a standard width, just make sure that the test equipment you wish to install in the rack conforms to the EIA-310-E standard. The standard width for rack enclosures is 24 inches or 600 mm, but wider enclosures are available that will accommodate cabling without obstructing airflow. This is especially important if your system must operate in an area without climate control.
Depth. When specifying the depth of your 19-in. rack, make sure that it will be deep enough not only for your equipment, but also any cabling. Take into account the minimum bending radius of the cables that you're using as well as the depth of the connectors. Exceeding the minimum bending radius will put undue stress on a cable and may cause it to fail earlier than anticipated.
42 inches is the standard depth for a 19-in. rack, but extra-deep (48 inches) rack enclosures are also available. If you do need extra depth, you may be able to adjust the depth of the vertical mounting rails in a four-post rack or rack enclosure, but only within certain limits. Shallower racks, including 36-in. (mid-depth) and 32-in. (shallow depth), are also available if your application requires that the rack fit in a small space.
Load Rating. The load rating (or weight capacity) of a rack specifies how much weight it can safely support. Add up the weights of all the equipment you plan to install in the rack and then add a safety factor to account for equipment that you may have to add at a later date. If you're going to be regularly moving the rack, look for the rolling or dynamic load rating as well as the stationary or static load rating.