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'[EE:] Wire Gauge'
2004\09\04@133112 by David Challis
2004\09\04@162535 by olin_piclist
2004\09\05@063231 by Nate Duehr

Olin Lathrop wrote:
> David Challis wrote:
>
>>The AWG "Wire gauge is the resistance per unit length in decibels,
>>where 10 AWG wire has 1 ohm per thousand
>>feet resistance."
>
>
> Decibels doesn't make sense in this context.  I guess they are really trying
> to say
>
>   gauge = 10 * Log10(mOhms / foot) ?
>
> But that implies that really fat wires have a negative gauge.  #0 cable
> would have 100uOhms/foot and have 3.2 times the diameter of #10.  Anything
> bigger would have to have a negative guage, although I've never heard of
> that.  Of course, I haven't worked with such fat cables either, so maybe
> they do have negative gauge numbers.  Or maybe by that size they are called
> something else, like "bus bars" and have a whole different numbering system?

Kinda.  Zero gauge is also known as 1/0 or "one aught".  The next bigger
size is 2/0 or 00 or "two aught".  And so forth, and so on.

Solid copper becomes a pain in the butt above about 4/0, but a lot of
times you see stranded construction stuff that goes much much bigger, of
course, and a few manufacturers put crazy stuff like 8/0 on the outside
jacket trying to say the stuff is the equivalent of a solid copper wire
that is that gauge.

Main distribution legs that are 1" or greater cross-section stuff in the
-48VDC battery systems at a telco central office is pretty common, that
stuff looks like small fire hoses.  And I got to see some again here
recently on a trip where some equipment I was responsible for was
installed in a CO.

The fun thing to see was the tool they use to crimp together cables that
size.  It looks similar to a "Sawsall" that is battery operated but its
only purpose in life is to crimp these huge sized cables to each other
using special soft metal rings that have two holes in them the size of
the cable.  Both cables are inserted and then the tool clamps down in
and crushes in a circular fashion -- for the first few, it was
fascinating to watch.  (Hey nothing like that is too interesting after
the first five or six of them.)

And I was more than willing to let those much-maligned Union
electricians climb around in overhead racks installing those, while I
remained planted firmly on the ground.  It was only about $6 million
dollars worth of hardware they were building the power distribution
system for, while climbing around like monkeys overhead... I figured I'd
leave that liability to them.

Each of our systems pulls about a max of 10-12A at -48VDC, and each
cabinet has two of those, two Cisco switches (~.2A @ -48VDC), a cabinet
fan, and a remote power switching device to be able to turn any of those
devices on and off remotely, making for a maximum load of about 26-27A @
-48VDC per cabinet.  The full load is wired to the power switching
device and then broken out from there for the various hardware.  Six
cabinets of that and two more cabinets of supporting hardware running on
AC.  The main distribution frame for the power was about 30 cable feet
from the equipment, and then the distance from there to the battery
plant down the hall was easily over 150 cable feet.  Not a power system
to be messed with by non-professionals, for sure.

Would have been a fun trip -- if it hadn't been to New Jersey and the
hotel where we played "Name that Stain" with the carpet in the rooms.

--
Nate Duehr, spam_OUTnateTakeThisOuTnatetech.com
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2004\09\05@085508 by Bob Ammerman

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