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Define: EIA-310

What is EIA

EIA stands for the Electronic Industries Association. The current revision is
EIA-310-D. The EIA-310 document is available for purchase at the IHS website.

Overview

EIA-310 is a specification for what is often called the “standard rack”.
This specification standardizes several important features of 19″ racks, such as
the Rack Unit (RU or
U), vertical hole spacing, horizontal hole spacing, rack opening and front
panel width. The specification also sets tolerances on each of these
dimensions.

The EIA-310 specification has been the 19″ racks standard for equipment for
50 years. Despite this, RackSolutions believes that the items that the
specification does not cover is the real reason for the industry wide
incompatibility we now face. Rack features such as hole type, rack mounting
depth, front and rear space, and obstructions between front and rear rails are
the cause of real rack headaches.

Vertical Hole Spacing

Vertical hole spacing is defined as a repeating pattern of holes within one
Rack Unit of 1.75″. The hole spacing alternated at: 1/2″ – 5/8″ – 5/8 and
repeats. The start and stop of the “U” space is in the middle of the 1/2″
spaced holes. See the diagram below.

Horizontal Spacing

The horizontal spacing of the vertical rows of holes is specified by EIA-310
at 18 5/16″ (18.312)(465.1 mm). This dimension is not well maintained on some
racks, causing problems with equipment installation. Many manufacturers use
equipment mounting slots instead of holes to allow for variations in this
dimension.

Rack Opening

The opening in the rack is specified as a minimum of 17.72″ (450mm). 2Post
or relay racks tend to have a larger than normal opening, as do many other racks
with threaded holes. Square hole racks tend to be very close to the minimum
opening.

Front Panel Width

The only dimension on a 19″ rack that actually measures 19″ is the width of
the front panel of equipment.

More Information

What is a 19″
Rack

What is a Rack
Unit (“U” or “RU”)

Wikipedia has an in-depth overview of 19″ racks.

Why
all racks are not created equal

Written by bob

This entry was posted on
Thursday, October 11th, 2007 at 10:40 pm and is filed under Popular, Terminology. You can follow any responses to this
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18 Responses to “Define: EIA-310”

Raul Cortes Says:
October
26th, 2007 at 3:09 pm

Horizontal Spacing. 465 mm = 18.307″.

Regards!

Bob Mimlitch Says:
October
26th, 2007 at 10:43 pm

Yep. 18.312″ (18 5/16″) = 165,10448mm. I’m sure they rounded it off.
However, the EIA-301 RevD states 465mm. The older EIA-301 RevC uses 18 5/16″
(18.312″), so you’re both right.

Craig McCluskey Says:

November
9th, 2007 at 10:41 am

http://electronics.ihs.com/collections/abstracts/eia-310.htm
says,

Section 1
Description: This section is the soft metric
conversion of the superseded EIA-310-C to
conform with U.S. Public Law
100-418.

I’m sure this means rounding off.

It also says,

Section 2
Description: This section is an adaptation of IEC
917 recommendations for Cabinets,
Racks and Panels. It is compatible
with the IEC 25 millimeter practices….

Whatever 25 millimeter practices are. Is that different than 25.4 mm = 1
inch?

Craig

Joseph B. Mattheeussen Says:
April
8th, 2008 at 4:57 pm

Actually, the ‘correct’ mm to inch Conversion Standard is the inverse of
.03937″ (=’s 1mm)… Therefore the EXACT inverse is actually:
25.400050800101600203200406400813, or 25.40005 for short!!! Multiply any
‘inch’ number by the Conversion factor of 25.40005 and you get the mm
equivalent, and the opposite goes by dividing the ‘X’mm number by the
Conversion factor to get the actual inch equivalent… -Can you tell I’m a
Design Eng’r?!

J Edelson Says:
May
23rd, 2008 at 12:58 pm

Not quite:

As _currently_ defined, the inch is 2.54 cm _exactly_.

When the US congress adopted the meter as the standard of measure (in the
mid 1800’s), it also adopted the standard that a yard was exactly 3600/3937 of
a meter, which made the meter 39.37″ and the mm 0.03937″ as Joseph states.

However in the mid 1900’s the inch was _redefined_ to be 2.54 cm.

This leads to there being two different definitions of the foot in common
use. The ‘survey foot’ uses the old definition.

Alwyn
Castelino Says:
July 15th, 2008
at 8:04 am

when US congress adapted they didnt clealy seen mfg facility available
around the globe! so nobody belives in US standards as practice for more
sophiticated work we can adapt 25.400050800101600203200406400813mm=1″
but
as we go do the enclosure or any panel work there its difficult to maintain
the acuracy

cheeerz

Ken Morenz Says:

January
27th, 2009 at 4:54 pm

OMG this is funny. There’s a debate over a 0.0002% error in the definition
of a millimeter / inch conversion about something that probably varies 1% or
more.

Carlos Says:
February
5th, 2009 at 2:12 pm

Y cual es el estandar del calibre de los parales para los Rack´s
????????

Jakob Bohm Says:

March
29th, 2009 at 11:06 am

Mr. Castelino is wrong here, Mr. Edelson is right. The change from
1/0.03997 to 25.4 by US congress was BECAUSE of mfg facilities around the
world becoming a reality. The other countries still using inches at the time
almost simultaneously passed similar laws or regulations adjusting their
(slightly different!) conversion ratios to 25.4 too. The only people still
using the 0.03997″ ratio are a few ultra-conservative industries (such as US
surveyors) and people who were taught the wrong ratio from outdated
schoolbooks.

That said, this article commits the deadly sin of randomly rounding
specifications differently and inconsistently. If you want to be inexact, do
it consistently. 18.312″ (465.14mm) OR 18.31″ (465.1mm) OR 18.3″ (ca. 465mm)
OR 18 5/16″ (ca. 46 1/2 cm). The ca. (circa) in front of 465 mm is needed
because 465 looks like a human-chosen exact specification, even though it is
not.

What is truly missing from this article are actual tolerance ranges for
each number (e.g. the center distance of holes should be at least 18.???”
(46?.? mm) and at most 18.???” (46?.? mm) but in reality varies between 18.?”
(46? mm) and 18.?” (46? mm).

A W Covert Says:
April
28th, 2009 at 9:15 am

RE: Front panel width definition above:

A SMART equipment manufacturer will make his faceplate slightly smaller
than 19″ – such as 18-31/32″ to avoid any problems with rubbing in tight
racks.

I once had an AP Audio patch bay that actually measured 19-1/32″ and would
not go into my all-steel welded rack (Premier or Bud). I e-mailed the mfg. and
they said they saw no problem with it becuase no one else had complained
before! Well, not everyone has cheap plywood racks with enough ‘give’ in the
sides.

By the same token, I suppose a smart rack manufacturer would error a little
on the wide side when spacing his (recessed) rails.

This kind of goes along with Jakob’s statement above where he notes “What
is truly missing from this article are actual tolerance ranges for each
number”. Amen!

Sintesis modular (Parte 1) | Racó tècnic
Says:
July
5th, 2011 at 11:45 am

[…] albergar servidores. Las medidas del formato se basan basada en las
espeficaciones definadas en la EIA-310 . El ancho esta normalizado, siempre es
de 19″, recordemos que 1″(pulgada) = 2,54cm .·. […]

jwood Says:
July
5th, 2011 at 11:53 am

English translation to the Spanish post above: host servers. The
measurements are formatted based on the specs defined in EIA-310. The width is
standardized, it is always 19 “, remember that 1″ (inch) = 2.54 cm

Sam Says:
July
31st, 2011 at 9:09 am

Is the propoer term EIA or has it been changed to CEA?

jwood Says:
August
2nd, 2011 at 2:56 pm

Good question. We are researching this. Per Wikipedia, EIA was dissolved in
Feb, 2011. Thanks for bringing it to our attention.

Don Says:
October
23rd, 2011 at 11:10 am

Looking for definitive history of the relay rack dimensions which seems to
be lost. Who (what person) or company was the initial designer of the
dimensions we use in relay racks, why were those dimensions picked and when
and what were the circumstances that started it all. All I’ve been able to
find is vague references to the old railroad signaling relays. What happened
to the history that created these specific dimensions? We just all have
‘accepted’ them because they are there??

jwood Says:
October
24th, 2011 at 4:01 pm

Don,
Wish we could help, but we don’t know the origin or history of the
2 post, relay rack either.
-RackSolutions Support

What is a rackmount server? by Kenneth Andrews |
Inside Technology 360 Says:
February 11th,
2014 at 8:03 am

[…] can be slotted into the rack on sliding rails and fastened to the rack
frame with screws. The industry standards for 19-inch racks have been in place
for more than half a […]

Observations… › Rack water cooling Says:

October
13th, 2015 at 10:19 pm

[…] based the spacing for the rails off the EIA-310 standard. If you don’t
want to take measurements and figure the math on this, you’ll want to
[…]

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