larry@uunet.uu.net (Larry Lippman) (10/08/90)
In articles <13072@accuvax.nwu.edu>, <13103@accuvax.nwu.edu> and <13127@accuvax.nwu.edu>, Donald E. Kimberlin, Thomas J. Roberts and haynes@ucscc.ucsc.edu discuss and ask questions about the 19" rack standard. I have commingled the quotes from their articles in order to create a logical flow and shed further light on this issue. > >I do not know if this is the right forum to ask this question but > >since the telecom history goes back more than 100 years it is worth > >a try. > Any technology historians out there for this one? > Let's get nit-picky about trivia. :-) You came to the right place, and to the right person. :-) In the Bell System and WECo world, rack mounted telephone apparatus as we know it today did not begin to develop until about 1917. Prior to that time, apparatus was chiefly constructed in wooden boxes which sat on the floor or hung on walls. Anyone who has ever seen pictures of the first transcontinental telephone line repeater systems will know exactly what I mean. The requirement for repeaters seemed to spur the development of relay racks and a dimensional standard, and as far as I know, sometime between 1917 and 1920 the 23" mounting plate and relay rack standard was born. The first WECo product that I know of to utilize the 23" mounting plate was the 22-type voice frequency repeater, which made its debut in 1920. The 23" WECo standard was based upon mounting plates in 2" increments, with vertical relay rack mounting holes on 1" centers. > >When and by whom was the 19" rack standard invented ? Sometime during the 1920's, and probably by RCA. WECo also made use of 19" apparatus beginning in the 1920's, but its use was primarily restricted to transmission measurement apparatus and other apparatus specifically related to radio communication. The 19" standard (today called EIA) made use of apparatus mounting plates in 1-3/4" increments, with relay rack mounting holes in three-hole spacing increments of 5/8"-5/8"-1/2". While 19" is by far the most common panel width, the EIA standard also covers panels in widths of 24" and 30". Please note that an EIA width is 24" and *not* 23" (a common misconception). > As a matter of interest, you will be surprised to see how many > manufacturers violate the standard in various details. If you have > been engaged in rack-mounting equipment of various vendors, it is not > at all unusual to have to perform some hacksaw, hammer and file > surgery in the process. Tell me about it! Special thanks for notable aggravation in past years go out to Specific Products (frequency standard receiver), Pacific Measurements (digital precision microwave power meter) and various apparatus made by Singer Metrics Division. :-) > I cannot speak to the issues of what corner of history this method > came from, but have reason to believe it predates the Bell hegemony, > dating back to days of peak Western Union influence. I don't believe the 19" rack was originated by Western Union, but I cannot be certain. > BTW, 19 inches is not the only "standard." Bell electronics equipment > most commonly uses 23 inch racks, while "frames" of electromechanical > switching equipment mount in 30 or even 36 inch widths, all using the > same 1-3/4 inch vertical increments. The WECo apparatus standard for 23", 30" and 36" mounting plates are *all* based upon a 2" mounting plate increment with 1" vertical hole spacing. > I do know the US inch-dimensioned racks all have whole-unit metric > equivalents. Because the inch-dimensioned racks do not actually come > out to exact inches, the root might well be some European imports of > antiquity that set the norm for the US. Interestingly enough, the 1970's vintage Japanese wire spring relay-crossbar PABX, such as those made by Hitachi, NEC and OKI, generally used the WECo 36" mounting plate for both relays and crossbar switches. > As this is a telecom newsgroup, I feel compelled to mention that AT&T > equipment racks [5ESS(Tm)] are usually 22.5" wide. Ah, yes the WECo ESS mounting frames. This began as a 23" U-shaped mounting plate whose width was extended by 1/2" of flat metal on each side so that it would mount from *behind* the frame. All traditional 23", 30" and 36" apparatus plates mount from the *front* of the frame. Then there was the WECo 770 and 800-series PABX's which used 36" plates which also mounted from behind the swing-out frames. In closing, I have a special treat for John Higdon. John's favorite :-) telephone company and apparatus manufacturer, GTE/Automatic Electric, has yet another rack standard for some electromechanical switching apparatus: 18-3/8" wide. I will further make John's day by admitting that I have personally experienced aggravation over being unable to mount any 19" apparatus in such frames. :-) Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry VOICE: 716/688-1231 || FAX: 716/741-9635 {utzoo||uunet}!/ \aerion!larry