Ask the Ranger: How do I Read the Dimensions of a Rackmount?
I am planning to put my home entertainment system on a rackmount frame. I have never used rackmount and do not understand the dimension listed. Particularly, is a 19� rackmount 19� wide? If not, what is the usable width?
The short answer to this question is nominally 17.5� of usable width. If you would like to know how this came about and have no fear of the unknown, then read on!
There are three standard rack widths related to Datacom and telecom. These are 19, 23 and 24 inches respectively. 19 inch is standard for Datacom. 23 inch is standard for telecom, and 24 inch is a combination broadcasting/telecom standard that is not that much in use today.
The components designed to fit these standards are not the same width as the standard. Only the faceplate or rack ears (features of the component that have the ability to support the component when it is mounted in the rack) has the standard width. When a component needs to be supported at all four corners, there is typically a rear mounting bracket (or brackets) that are also the standard width. The rest of the component is normally about 1.5 inches narrower than the standard width.
The best way to explain this is to look at two simple rackmount components:
· two post relay rack
· blank panel
The two post relay rack is a pair of vertical uprights that have mounting holes. A base, and a top provide the support structure to keep the rack square, upright, and with the same mounting width from top to bottom. You can mount 19 inch components in a 19 inch relay rack. The simplest component is a flat blank panel. The flat blank panel is exactly 19 inches wide. To install it, place the panel up against the uprights of the relay rack. Line up the holes in the panel with the appropriate holes on the rack, insert the correct screw (based on screw size and number of threads per inch), tighten, and voila! Now you have installed a blank panel on a relay rack. The same process works for any rackmount component. However, with something other than a blank panel, there is a “body� or chassis attached to the blank panel, and in order to get this “body� to pass between the uprights, it cannot be 19 inches wide. It cannot exceed the free space between the uprights, which is normally called the “pass through distance.� The pass through distance is usually in the range of 17.5 to 17.75 inches wide, although this varies with different manufacturers and types of racks. So a typical 19 inch rackmount component is about 17.5 inches wide with a face plate or rack ears that provide the actual 19 inch width.
