Cabinet and Rack Mounting of Electronic Equipment

Introduction

A rack is a floor standing structure capable of supporting chassis of electronic equipment. Early mounting of electronic equipment consisted primarily of these open air racks.

A cabinet is simply an enclosed rack. Cabinets are used in most applications today because they are more attractive, provide more protection, and because over-heating is no longer as much of a problem.

Height (Mounting Hole Patterns)

Vertical mounting members of racks or cabinets provide mounting holes for attaching front panels and chassis slides. These holes are normally the Universal RETMA hole pattern recognized by the Electronic Industries Association. Occasionally, however, the obsolete Western Electric hole pattern is used. Both hole patterns repeat every 1 3/4 inches. For this reason, the height of standard chassis front panels are made in 1 3/4 inch increments, (less 1/32 for clearance).

IMPORTANT DESIGN CONSIDERATION: Top and bottom edge of chassis front panels should be centered on 1/2 inch hole spacing. See the illustration below.

Chassis Front Panel Configurations

There are two standards which determined the location of mounting slots on chassis front panels, one of which is cancelled. Mil-Std-189 (cancelled) was established over 50 years ago and was based on the Western Electric hole pattern. The Electronic Industries Association  (EIA) RS-310 specification is based on the RETMA hole pattern. The table below illustrates the two standards.

Standard Front Panel Sizes and Slot Locations

Panel Height

Mil-Std-189 (Cancelled)

EIA RS-310

Figure 

Number
 of RETMA
Increments

Effective

Actual

A B C D A B
1 1 3/4 1.719 1.25       1.25   1
2 3 1/2 3.469 3.00       3.00  
3 5 1/4 5.219 2.25       2.25   2
4 7 6.969 4.00       4.00  
5 8 3/4 8.719 2.25 1.75     5.75  
6 10 1/2 10.469 3.00 2.25     3.00 2.25 3
7 12 1/4 12.219 5.75 1.75     2.25 3.50
8 14 13.969 4.00 3.50     3.00 4.00
9 15 3/4 15.719 5.75 3.50     4.75 4.00
10 17 1/2 17.469 7.50 3.50     6.50 4.00
11 19 1/4 19.219 5.75 5.25     5.75 5.25
12 21 20.969 4.00 5.25 1.75   7.50 5.25
13 22 3/4 22.791 5.75 1.75 5.25 4
14 24 1/2 24.469 7.50 5.25 1.75
15 26 1/4 26.219 5.75 7.00 1.75
16 28 27.969 4.00 3.50 5.25 1.75     5
17 29 3/4 29.719 5.75 3.50 5.25 1.75    
18 31 1/2 31.469 7.50 3.50 5.25 1.75    

Slide Mounting Height

The diagram below illustrates the recommended mounting heights of the various Chassis Trak slide models. Mounting heights shown represent the distance from the bottom of the chassis front panel to the centerline of the slide. Figures are based on MIL-STD-189 or EIA RS_310. These panels are available in increments of 1 3/4 inch (less 1/32 inch clearance between panels.

Cabinet Width

Ideally, chassis width plus thickness of the slides should equal the clear opening width of the cabinet. This table describes standard chassis widths and the clear opening widths of cabinet.

 

Cabinet Clear Opening Width

Cabinet Front
Panel Width

Chassis
 Width

Minimum
 Standard

Most Cabinets

Vent Rak
 Cabinets

19 17 17.750 17.781 17.812 17.937
24 22 22.750 22.781 22.812 22.937
30 28 28.750 28.781 28.812 28.937
Maximum Allowable
Slide Thickness
.375 .390 .406 .468