battan@qtc.UUCP (Jim Battan) (08/18/89)
I hear that "RETMA rails" are the standard 19" rail spacing in all computer equipment racks. What does the "RETMA" acronym stand for? Who defined the "standard"? -- Jim Battan uunet!sequent!qtc!battan +1 503 626 3081 Quantitative Technology Corportation (QTC) 8700 SW Creekside Place, Suite D Beaverton, OR 97005
mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti) (08/18/89)
In article <447@qtc.UUCP> battan@qtc.UUCP (Jim Battan) writes: >I hear that "RETMA rails" are the standard 19" rail spacing in all >computer equipment racks. >What does the "RETMA" acronym stand for? I recently needed the nominal dimensions of rack stuff for a personal project and one of the mechanical designers where I work gave me a photocopy of a photocopy of a ... of _RETMA Standard SE-102, Panel Mounting Racks, Panels, and Associated Equipment_. RETMA is the _Radio-Electronics-Television Manufacturers Association_. The standard was first published in February of 1919 (no typo, that's 1919!). The copy I have indicates it was reprinted in March of 1931. I have no idea whether RETMA is still active, but the document gives an address of 777 14th St, N.W., Washington 5, D.C. (Remember postal zone numbers? No zip codes in 1931!) >Who defined the "standard"? RETMA! -- ============================================================================ Michael Kesti Grass Valley Group, Inc. | "Like one and one don't make two, mrk@gvgspd.GVG.TEK.COM | one and one make one." !tektronix!gvgpsa!gvgspd!mrk | - The Who, Bargain
cdl@mplvax.EDU (Carl Lowenstein) (08/19/89)
In article <447@qtc.UUCP> battan@qtc.UUCP (Jim Battan) writes: >I hear that "RETMA rails" are the standard 19" rail spacing in all >computer equipment racks. >What does the "RETMA" acronym stand for? Radio Electronic Television Manufacturers' Association >Who defined the "standard"? Nobody all at once, it just sort of happened. Here comes some history from memory, since I haven't seen the printed references in 25 years or more. First there was Western Electric (WE), who made equipment for telephone systems. They wanted to mount their relays in relay racks (naturally), and chose to do so on panels that were multiples of 1.75 inches high. To fasten the panels to the racks, a pattern of holes was devised that repeated every 1.75 inches. Pairs of holes 0.5 inches on center. So the over-all hole pattern was alternating 0.5 inch and 1.25 inch spaces. Each panel fit with its edges between a pair of 0.5-inch spaced holes. Next there was the radio broadcasting industry, who also wanted to mount things neatly in racks. Perhaps not electronic things, since the word Electronics did not become widely used until the mid to late 1930's. Nevertheless, the Radio Manufacturers' Association (RMA) chose to use panels which were a multiple of 1.75 inches, but they decided on a hole pattern for the rack which was just a uniform 1.75 inches everywhere. Each panel fit with its edges between a pair of 1.75-inch spaced holes. Radio amateurs, who scrounged equipment from everywhere, soon noticed that WE panels would only sometimes fit RMA racks, and vice versa. Eventually, there was a great compromise when somebody noticed that a rack could be drilled with the inclusive OR of the two hole patterns. So it is unto this day that the 1.75 inch repetition of the hole pattern consists of 0.5 inch, 0.625 inch, 0.625 inch. And the edge of the panel still fits between the 0.5-inch spaced holes, which happens to be also the mid-point of a pair of 1.75-inch spaced holes. Along the way, the RMA diversified itself, as there came to be Electronics and Television, so there was the Radio Electronics Television Manufacturers' Association (RETMA). Eventually they gave up on adding new nouns to their title, and ended up as the Electronic Industries' Association (EIA). And this, my dearly beloved, explains why some equipment still doesn't fit in its rack. It is off by 0.25 inch one way or the other, because somebody doesn't know the difference between the 0.5-inch hole pairs and the 0.625-inch hole pairs. -- carl lowenstein marine physical lab u.c. san diego {decvax|ucbvax} !ucsd!mplvax!cdl cdl@mpl.ucsd.edu