Re: DC power versus AC power

[Owen DeLong]

Also, some AC circuit breakers are of a design that counts on the magnetic
properties of AC, and, therefore, won't trip due to ANY DC load.  I think
these are mostly not available any more, but I remember encountering them
some time ago and realizing that it would be _REALLY_ bad if someone put
them in a DC plant accidentally.

Owen


--On Monday, December 30, 2002 9:18 -0500 "Robert E. Seastrom" 
<[EMAIL PROTECTED]> wrote:



"Barton F Bruce" <[EMAIL PROTECTED]> writes:


Typical 120/208V small branch circuit breakers in small buildings and
homes have an interrupting capacity rated at 10,000 amps, and should not
be deployed where that can be exceeded. It will be on the label.


It's worth noting that the interrupting capacity of the aforementioned
breakers is 10,000 amps *AC*, and that said circuit breakers should
not be used in *DC* applications despite the fact that the voltage is
less than half as much and the fact that they're downstream from a
600A fuse (and have smaller wire in the circuit that will naturally
limit how many amps can go into a short anyway).

I'm hazy on the theory (perhaps someone more knowledgeable can post
it), but my understanding is that with AC the arc has a chance to
quench 120 times per second (ie, every time there's a zero crossing),
and with DC that opportunity (obviously) does not exist.

Bottom line is that one should buy breakers and fuses that are
designed for use in DC powerplants, rather than trying to cheap out
with something you picked up at Home Depot or Pep Boys.  I'm sure I'm
wasting my breath since _nobody_ who reads NANOG would ever try to cut
corners to save a few bucks...  :)

---Rob

Re: DC power versus AC power

[Stephen Sprunk]

Thus spake Robert E. Seastrom <[EMAIL PROTECTED]>:
> "Stephen Sprunk" <[EMAIL PROTECTED]> writes:
>
>> Thus spake joe mcguckin <[EMAIL PROTECTED]>:
>>> It only takes 30ma to put your heart into atrial fibrillation. In
>>> the usa, gfi's are set to trip at 5ma.
>>
>> Did you mean 5A, or am I misunderstanding GFIs?
>
> it's 5ma.  http://www.national.com/ds/LM/LM1851.pdf

Perfect, thanks.

I learn so many interesting things on NANOG, it almost makes up for the
noise :)

S

Re: DC power versus AC power

[David Lesher]

I deny saying:

> But they are there for reason. They are typ. full of power to

powDer



-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[Robert E. Seastrom]

"Stephen Sprunk" <[EMAIL PROTECTED]> writes:

> Thus spake joe mcguckin <[EMAIL PROTECTED]>:
> > It only takes 30ma to put your heart into atrial fibrillation. In the
> > usa, gfi's are set to trip at 5ma.
> 
> Did you mean 5A, or am I misunderstanding GFIs?

it's 5ma.  http://www.national.com/ds/LM/LM1851.pdf

---rob

Re: DC power versus AC power

[Steven M. Bellovin]

In message <004f01c2b018$4ac14900$[EMAIL PROTECTED]>, "Stephen Sprunk" wr
ites:
>
>Thus spake joe mcguckin <[EMAIL PROTECTED]>:
>> It only takes 30ma to put your heart into atrial fibrillation. In the
>> usa, gfi's are set to trip at 5ma.
>
>Did you mean 5A, or am I misunderstanding GFIs?
>

No -- 5 ma is correct.  (GFIs measure the difference in current between 
the hot and neutral leads -- if it exceeds 5 ma, it trips.)

--Steve Bellovin, http://www.research.att.com/~smb (me)
http://www.wilyhacker.com (2nd edition of "Firewalls" book)

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Stephen Sprunk said:
> 
> 
> > It only takes 30ma to put your heart into atrial fibrillation. In the
> > usa, gfi's are set to trip at 5ma.
> 
> Did you mean 5A, or am I misunderstanding GFIs?

5ma is correct.
It takes very little current to cause fibrillation.

GFI's compare the current going out the hot lead of a receptacle
with that coming back the neutral. If there is more out than back,
it makes the assumption the rest is going through Jill Winecooler/
Joe Sixpack to ground, and trips.




-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Robert E. Seastrom said:
> 
> Bottom line is that one should buy breakers and fuses that are
> designed for use in DC powerplants, rather than trying to cheap out
> with something you picked up at Home Depot or Pep Boys.  I'm sure I'm
> wasting my breath since _nobody_ who reads NANOG would ever try to cut
> corners to save a few bucks...  :)

Gawd yes. 

We all know those little 3AG glass fuses, right? They also come
in ceramic. A regular PITA -- you can not look and see they are
blown.

But they are there for reason. They are typ. full of power to
quench the resulting arc. A glass 3AG can and will open, yet the
arc just keeps goingslagging the fuseholder, and whatever was
errr... protected.

There is as much diversity and engineering in fusing as router
design. Voltage to be broken, AC vs DC, time curve to open, other
factors all enter into it. I see two fuses in series on "pole pigs"
primaries around here. Finally had a chance to ask the foreman.
One is {say} 10A and that is sized for overloads. The second is
15A, but its sole function is to open FAST if the primary takes a
lightning hit and the spark-gap on the transformer conducts. Seems
they can't get both qualities right in one fuse so they use two.

And RES is correct; DC circuit breakers are different animals than
AC by a long shot. Fuses have different ratings as well. RTFM.


Please be careful; while you might [now] be easily replaced, the
suffering VC's will not appreciate losing all to a dropped tool.


ps: I've not even mentioned the acid and H2 gas [kaaBOOM] issues...


-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[Stephen Sprunk]

Thus spake joe mcguckin <[EMAIL PROTECTED]>:
> It only takes 30ma to put your heart into atrial fibrillation. In the
> usa, gfi's are set to trip at 5ma.

Did you mean 5A, or am I misunderstanding GFIs?

> Normally 48VDC wouldn't be considered a 'lethal' voltage (I've talked
> to telephone technicians who said they used to play a game in the CO
> by wiring a handle to 90V ring voltage and seeing who could grab it
> for the longest time),

That explains so many things...

S

Re: DC power versus AC power

[Robert E. Seastrom]

"Barton F Bruce" <[EMAIL PROTECTED]> writes:

> Typical 120/208V small branch circuit breakers in small buildings and homes
> have an interrupting capacity rated at 10,000 amps, and should not be
> deployed where that can be exceeded. It will be on the label.

It's worth noting that the interrupting capacity of the aforementioned
breakers is 10,000 amps *AC*, and that said circuit breakers should
not be used in *DC* applications despite the fact that the voltage is
less than half as much and the fact that they're downstream from a
600A fuse (and have smaller wire in the circuit that will naturally
limit how many amps can go into a short anyway).

I'm hazy on the theory (perhaps someone more knowledgeable can post
it), but my understanding is that with AC the arc has a chance to
quench 120 times per second (ie, every time there's a zero crossing),
and with DC that opportunity (obviously) does not exist.

Bottom line is that one should buy breakers and fuses that are
designed for use in DC powerplants, rather than trying to cheap out
with something you picked up at Home Depot or Pep Boys.  I'm sure I'm
wasting my breath since _nobody_ who reads NANOG would ever try to cut
corners to save a few bucks...  :)

---Rob

Re: DC power versus AC power

[Barton F Bruce]

A few points:

Below 50 volts, anyone can do the wiring. No licensed electrician is needed
im most jurisdictions.

Total fault current available determines the damage that will be done when
something like a wrench falls across bus bars. Time, too, counts. If you
can't vaporize the whole wrench before the upstream fuse or breaker opens,
then you just have scarred metal. For any given load, the AC wiring, running
higher voltage than 48VDC CO batteries, will be smaller due to the lower
amperage requirements and the larger typically allowed voltage drop.

The AC network's source impedance is going to be a lot higher than a local
battery string. too.

A 600 amp capacity BDFB panel in a COLO room even just a 100' of cable loop
length (50' end to end) from the main fuse panel at the batteries may well
be wired with excess ampacity just to limit the IR drop. Instead of just a
single 535MCM cable (that has adequate ampacity) that might mean up to
3x535MCM or 2x777MCM in parallel for both battery and return for both A and
B battery feeds! That is a lot of copper.

Look at the current available from a typical 9,000 ampere hour battery
through just a single 100' length of 750MCM cable that has a resistance of
.00150 ohms, assuming, for simplicity no resistance for the battery. That is
48 / .00150 = 32,000 amps, and that is very comfortable short term for a
battery that can deliver 9,000 amps for an hour!

The cable between the battery and the main fuse panel is unprotected other
than by the ability to vaporise the straps between cells that are often
substantially smaller in cross section than the cable. After the main fuse
panel, typically there would be a 600 amp fuse protecting the feed to a BDFB
Before that fuse goes, there is still plenty of energy to vaporize common
hand tools.

Typical 120/208V small branch circuit breakers in small buildings and homes
have an interrupting capacity rated at 10,000 amps, and should not be
deployed where that can be exceeded. It will be on the label.

Some carriers have reservations about the small plug in (bullet pins on
rear) BDFB panel breakers that in one case size range from a few amps to
100. Apparently there have been fires, and fuses are considered safer.

Once you get past dry skin resistance, I have several times seen human body
resistance given as 1 ohm. I have no idea how/where that is being measured.

Re: DC power versus AC power

[joe mcguckin]

It only takes 30ma to put your heart into atrial fibrillation. In the usa,
gfi's are set to trip at 5ma.

Normally 48VDC wouldn't be considered a 'lethal' voltage (I've talked to
telephone technicians who said they used to play a game in the CO by wiring
a handle to 90V ring voltage and seeing who could grab it for the longest
time), but you've got to consider the extreme cases where the working
environment may be wet or a worker could get exposed through open wounds,
puncture wounds or mucus membranes.

Under the right circumstances, nearly any voltage can be lethal.

Joe



On 12/29/02 5:40 PM, "Scott Granados" <[EMAIL PROTECTED]> wrote:

> 
> Is 48V DC at the amps present normallyin switch rooms etc enough to cause
> electricucian?  I have seen bad things with wrenches dropped across
> batteries even 12 volt car batteries although in this case it was a large
> battery bank in a submarine but I was curious about the 48V sources in
> switch rooms.
> 
> 
> 
> - Original Message -
> From: "David Lesher" <[EMAIL PROTECTED]>
> To: "nanog list" <[EMAIL PROTECTED]>
> Sent: Sunday, December 29, 2002 4:43 PM
> Subject: Re: DC power versus AC power
> 
> 
>> 
>> Unnamed Administration sources reported that Michael Painter said:
>>> 
>>> 
>>> 
>>>>> But, as Stephen already eluded to... Compared with an AC plant
> design, to
>>> me, one of the biggest drawbacks of a DC plant is safety  (I have had to
>>> kick a fellow worker away from the rack before). <<
>>> 
>>> What was the worker doing?  Is this 48 VDC?
>> 
>> Bet so.
>> 
>> And note, it's not just ISP's, of course. I heard that Sprint
>> PCS ha[s,d] a Dallas tech in critical condition and a dead switch
>> after a dropped wrench & resulting fire.
>> 
>> In the words of Phil Esterhaus:
>> 
>> Let's be careful out there
>> 
>> 
>> 
>> 
>> 
>> --
>> A host is a host from coast to [EMAIL PROTECTED]
>> & no one will talk to a host that's close[v].(301) 56-LINUX
>> Unless the host (that isn't close).pob 1433
>> is busy, hung or dead20915-1433
>> 
> 

Re: DC power versus AC power

[Stephen Sprunk]

Thus spake "Scott Granados" <[EMAIL PROTECTED]>
> Is 48V DC at the amps present normallyin switch rooms etc enough to cause
> electricucian?  I have seen bad things with wrenches dropped across
> batteries even 12 volt car batteries although in this case it was a large
> battery bank in a submarine but I was curious about the 48V sources in
> switch rooms.

2500-class devices only need 2A, but a GSR needs 60A -- and 60A DC is
significantly more dangerous than 60A AC due to the duty cycle.

If you _remember_ to defuse/disable the leads from the A _and_ B fuse panels
to the device you're working on, you'll be okay.  The real danger is when
people are working on the "upstream" side of the power panel, which is often
difficult/impossible to defuse and carries significantly higher amperages.

S

Re: DC power versus AC power

[Stephen Sprunk]

Thus spake "Wayne Bogan" <[EMAIL PROTECTED]>
>
> For those AC only powered units, you can also purchase an invertor for DC
to
> AC conversion.  You would then have the advantages of DC for your AC
> equipment.  This does, however, add the potential of another point of
> failure such as fuses or breakers in the invertor.

Well, that's how AC UPS's work -- just beware what percentage of the input
current is lost in the conversion from DC to AC, plus what is lost
converting from AC back to DC inside the equipment.  Much simpler to specify
DC equipment to begin with if you really care about availability.

S

Re: DC power versus AC power

[Owen DeLong]

Absolutely.  Often, there are more than a few hundred amps available.
Remember, many of those switch rooms were built to specs to drive a very
large number of solenoids, relays, etc.  All relatively high-current
devices compared to today's solid state stuff.  Alot of the specs were
never reduced, the rooms just got bigger, and the number of customers.
There's a reason the backbone is multiple copper plates and not just
wire.

Owen


--On Sunday, December 29, 2002 5:40 PM -0800 Scott Granados 
<[EMAIL PROTECTED]> wrote:


Is 48V DC at the amps present normallyin switch rooms etc enough to cause
electricucian?  I have seen bad things with wrenches dropped across
batteries even 12 volt car batteries although in this case it was a large
battery bank in a submarine but I was curious about the 48V sources in
switch rooms.



- Original Message -
From: "David Lesher" <[EMAIL PROTECTED]>
To: "nanog list" <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 4:43 PM
Subject: Re: DC power versus AC power




Unnamed Administration sources reported that Michael Painter said:
>
>
>
> > > But, as Stephen already eluded to... Compared with an AC plant

design, to

> me, one of the biggest drawbacks of a DC plant is safety  (I have had
> to kick a fellow worker away from the rack before). <<
>
> What was the worker doing?  Is this 48 VDC?

Bet so.

And note, it's not just ISP's, of course. I heard that Sprint
PCS ha[s,d] a Dallas tech in critical condition and a dead switch
after a dropped wrench & resulting fire.

In the words of Phil Esterhaus:

Let's be careful out there





--
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Barney Wolff said:
> 
> 
> > I'm surprised you're still around after a sub battery accident.
> > They're a grade up from most CO's in available current, I'd bet.
> 
> I'd bet the other way.  CO battery has to supply ring current, dial
> tone and voice current, not just run the switch itself, at least
> in the Copper Age.  I don't think -48VDC is an electrocution risk
> unless you're sweaty, but a vaporized wrench sure can burn you, and
> I don't think GFIs existed for DC.
> 
> Anyway, nukes don't need the battery capacity of the old diesels.

 and
 


-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[David Lesher]

Ouch...

nas-corp.com is rejecting  me for "profanity"

Was it the 'sweaty' or the posterior term?

Jeeze


-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Michael Painter said:
> 
> 
> I've laid across the buss-bars before...definitely an uneasy feeling, but never
> felt it unless I was sweaty. 
>  Capability of thousands of Amps, but it's the old "power transfer"
> deal...internal resistance of the source vs. internal resistance of the load (your
> body).

True. It's all Ohms law. But for those of you who (unlike me)
speak C and mean a language, not 3E8m/s. let's look at
13.8v car battery and a 120v line cases.

Ohms are what resist the flow of [I'll say so even though I'll
wince] electrons.

I = E/R. I = current, E voltage, R resistance.

People are not good conductors; let's just say you have oh 100Kohm
from one DRY thumb to another. Most of that is skin. Get inside
the ?epidermous [sp]? and it goes down fast. Get even slightly
sweaty, and same deal.

So I = 13.8/100k is not much current. Not enough to hurt.

I = 120v/100K is 1.2ma. That's not enough to cook you, but
may be enough to screw up your heart. That's why the "one hand
rule" exists. Loop one hand through belt at your ass, work with
other. Iffen you get bit finger to finger on the same hand,
it won't pass though your trunk. (Assuming rubber shoes...)

Now, consider that dropped screwdriver. Say the total resistance
of it across the contacts is 0.05 ohms. (It's dirty...)

I = 13.8/0.05 = 276 A. Sparks fly. Tool melts, you hope.

I = 120v/0.05 = 2400 A. Here, the 20A breaker should clear as
fast as it can, and it's likely only going to be oh 1000A until
it does. Still shit flies and if your eyes are in the way...

Now, milliseconds later [if the fuse/breaker has not cleared]
that initial current gets enough things hot, melts/cleans parts,
LOWERING THE RESISTANCE as it ..improves..  the connection... 

Worst case, you get a plasma arc that LOVES to conduct.

In that case, the resistance goes to near zero. The current is
only limited by other resistances in the battery string, and you
have good tight connections and large cables, right? 

If you are lucky, the screwdriver is consumed and the short stops.
If not, well soon you get badly burnt. Wrenches are a lot more
massive; and will do more damage.

Some major burn cases live.  I'm not sure they are the lucky ones.


Short summary: 120vac line may "electrocute" you easily; a high
current lower voltage system can cook you just as dead. Neither
is "safe" to futz with casually.




-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

RE: DC power versus AC power

[blitz]

Just some musings...

Been watching this discussion for a couple loops now. I have to say you're 
both right on certain things, and that each individual design has to be 
done on the merits of the need for 100% uptime vs what's tolerable.

AC is always easier to run, as the conductors are smaller because the 
voltage is higher and I/R losses are smaller. It does not however, lend 
itself to staying alive in that time when the AC mains fail and the 
generator starts and gets itself online. For that one needs a battery.

From my days at one of the three letter telcos, we had huge battery banks, 
monstrous individual cells, that had ampacities that you can arc weld with 
with ease and never notice the drain. However, the conductors running 
around the sites were often the size of your wrist and the I/R drop in even 
these conductors was noticeable, especially when you had two ESS switches 
plus the transport gear on battery alone. We backed up the battery plant(s) 
with a 1 megawatt Cat diesel.

Both AC supply and DC have their places, both have limitations.
Obviously if its got to always be there-no-excuses-no-margin-for error, the 
costly battery solution is the only way. Batteries, copper, chargers, fuse 
panels, big wires. $$
Add maintenance.. yes, water boy...someone's going to have to check 
tightness of all those connections, as even a little looseness will turn a 
buss bar into molten metal at the amperages we are talking about here. 
Someone will need to test the capacity of the system from time to time 
under load conditions as well, to find cells going bad, and hot spots in 
the conductors. Liquid cells have specific gravity charts that need watched 
and water added as it evaporates. This makes them a maintenance job at 
regular intervals.

"If you don't do this now, under good times and daylight conditions, you 
WILL be doomed to do it under power failure, and no light conditions". -Sparky

One last thought on DC safety...there is a LOT of current in even one of 
these cells. I've seen a finger amputated when a wedding ring bridged a 
pair of conductors and a metal watch band vaporize when laid across a buss 
bar, resulting in 3rd degree burns. Typical voltages are 48v which is just 
low enough to give a sweaty arm a tingle to let you know the trons are 
there. Bridge them with a conductor and expect fireworks. Anyone working 
around batteries needs to have their head screwed on right. They are not 
typically dangerous, but you do have to make sure you observe the rules. 
You have high current, dangerous acid, and hydrogen gas present. You should 
treat it as you would any potentially dangerous industrial process, with 
respect.

Scale all this to the size of the battery plant you're contemplating using 
to protect your gear.
If I were designing a site, and had unlimited $, a battery plant would back 
it up. We stored 48 hours of electricity, enough time to repair or replace 
the generator.

If you can rely on your power feed in being there within a few seconds of a 
commercial mains failure, (your site has an adequate generator, which is 
maintained and tested regularly) you can usually get by with that lowball 
UPS system, one that youre going to lock away in a room or the bottom of a 
rack and forget about until the feces hits the air mover. You will, don't 
argue, I know you will. When the power's on, you don't pay attention to 
backup systems, please see "sparky" quote above.
I've even had idiots say "we cant test the UPS because, What happens if it 
fails? we go down"cant do that in the middle of a business day... yet 
they would never allocate some "night" time to test. Ok, see you next outage.
My idea of a UPS is take the maximum amount of power you need for your 
equipment now, and add 50% then double it.
The 50% is normal equipment additions, the double is for that weak battery 
two or three years down the road.

Ive run an ISP for three days during an Ice storm, using 4 tractor trailer 
batteries, and a great, big, over-rated UPS. Two batteries were online at 
one time, in parallel,  two were being charged from a 150 amp alternator on 
my truck to replace them in 4 hours. The secret here was plenty of battery, 
plenty of UPS. Never let the battery go dead, and be able to change out the 
parallel battery without loosing all power. A simple matter of planning. 
That little gel-cell inside your UPS is a 12 volt battery in all aspects. A 
tractor trailer battery is as well. You can always use a larger battery as 
room permits. If the UPS can handle the load, all you need to feed it is 
12v, car battery, truck battery, etc. all work. Just observe polarity, as 
you'll only get one chance if you do it wrong.

A word or two about Gell-Cells:
Gell cells are nice, and don't slop like liquid cells. There is a price you 
pay. Gelatin electrolytes have what's called an electron-mobility problem 
caused by the "Gelatin" in the electrolyte. Less current can be consumed at 
once, and inversely

Re: DC power versus AC power

[Scott Granados]

Yes it will the wrench will become litterally liquid and spray.  So no it
doesn't explode in the litteral sense but it appears to and also sounds like
it:).  A safe experiment to do which many people probably did as Kids is to
take a piece of tin foil and place it across the terminals of say a trainset
transformer or perhaps  a 6 V drycell battery that you set up with a proper
switch so you can switch on the flow when you are standing back.  The foil
will sizzle and pop used to be the way you could demonstrate how fuses
worked.  Imagine that but this time the wrench handle goes pop.

- Original Message -
From: "David Diaz" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "nanog list" <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 5:45 PM
Subject: Re: DC power versus AC power


>
> While I would normally think some of this exaggeration.  When I was
> at Netrail, I did a road trip to upgrade a facility in DC.  It's
> kinda amazing what passed for colo in those days.  The little UPS
> actually had a string of Pet boys car batteries.  Nathan Estes
> dropped a wrench into the battery bay and there was a nice explosion
> according to him.  The wrench literally vaporized.  Now I said that
> wasnt possible.  He will stick to his story to this day.
>
> The only thing I could figure was that it literally moltified into
> super small droplets and just sprayed.  Regardless of whether it's
> completely accurate, he was out searching for another wrench... it
> took a lot of chocolate mile to relax him after that.
>
>
>
>
> At 20:11 -0500 12/29/02, David Lesher wrote:
> >Unnamed Administration sources reported that Scott Granados said:
> >>
> >>  Is 48V DC at the amps present normallyin switch rooms etc enough to
cause
> >>  electricucian?  I have seen bad things with wrenches dropped across
> >>  batteries even 12 volt car batteries although in this case it was a
large
> >>  battery bank in a submarine but I was curious about the 48V sources in
> >>  switch rooms.
> >
> >
> >Electrocution is but one way to die from too many columbs.
> >Internal burning is a big one.  Most people die, not from immediate
> >cardiac arrest, but rather from kidney/spleen/liver failure as
> >they try to remove the cooked you parts from your bloodstream,
> >and clog up. (First responder treatment is multiple saline inputs
> >to flush you out, and keep flushing you. This via a friend who was
> >"lit" and lived.)
> >
> >The instantaneous short circuit current available from a CO-grade
> >battery string is nothing short of frightening. It will easily
> >turn a 18" crescent wrench bright orange and start spitting the
> >molten metal around within few seconds.
> >
> >I'm surprised you're still around after a sub battery accident.
> >They're a grade up from most CO's in available current, I'd bet.
> >
> >
> >
> >
> >--
> >A host is a host from coast to [EMAIL PROTECTED]
> >& no one will talk to a host that's close[v].(301) 56-LINUX
> >Unless the host (that isn't close).pob 1433
> >is busy, hung or dead20915-1433
>
> --
>
> David Diaz
> [EMAIL PROTECTED] [Email]
> [EMAIL PROTECTED] [Pager]
> www.smoton.net [Peering Site under development]
> Smotons (Smart Photons) trump dumb photons
>
>
>

Re: DC power versus AC power

[David Diaz]

While I would normally think some of this exaggeration.  When I was 
at Netrail, I did a road trip to upgrade a facility in DC.  It's 
kinda amazing what passed for colo in those days.  The little UPS 
actually had a string of Pet boys car batteries.  Nathan Estes 
dropped a wrench into the battery bay and there was a nice explosion 
according to him.  The wrench literally vaporized.  Now I said that 
wasnt possible.  He will stick to his story to this day.

The only thing I could figure was that it literally moltified into 
super small droplets and just sprayed.  Regardless of whether it's 
completely accurate, he was out searching for another wrench... it 
took a lot of chocolate mile to relax him after that.




At 20:11 -0500 12/29/02, David Lesher wrote:
Unnamed Administration sources reported that Scott Granados said:


 Is 48V DC at the amps present normallyin switch rooms etc enough to cause
 electricucian?  I have seen bad things with wrenches dropped across
 batteries even 12 volt car batteries although in this case it was a large
 battery bank in a submarine but I was curious about the 48V sources in
 switch rooms.



Electrocution is but one way to die from too many columbs.
Internal burning is a big one.  Most people die, not from immediate
cardiac arrest, but rather from kidney/spleen/liver failure as
they try to remove the cooked you parts from your bloodstream,
and clog up. (First responder treatment is multiple saline inputs
to flush you out, and keep flushing you. This via a friend who was
"lit" and lived.)

The instantaneous short circuit current available from a CO-grade
battery string is nothing short of frightening. It will easily
turn a 18" crescent wrench bright orange and start spitting the
molten metal around within few seconds.

I'm surprised you're still around after a sub battery accident.
They're a grade up from most CO's in available current, I'd bet.




--
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433


--

David Diaz
[EMAIL PROTECTED] [Email]
[EMAIL PROTECTED] [Pager]
www.smoton.net [Peering Site under development]
Smotons (Smart Photons) trump dumb photons

Re: DC power versus AC power

[Barney Wolff]

On Sun, Dec 29, 2002 at 08:11:46PM -0500, David Lesher wrote:
> 
> I'm surprised you're still around after a sub battery accident.
> They're a grade up from most CO's in available current, I'd bet.

I'd bet the other way.  CO battery has to supply ring current, dial
tone and voice current, not just run the switch itself, at least
in the Copper Age.  I don't think -48VDC is an electrocution risk
unless you're sweaty, but a vaporized wrench sure can burn you, and
I don't think GFIs existed for DC.

Anyway, nukes don't need the battery capacity of the old diesels.

-- 
Barney Wolff http://www.databus.com/bwresume.pdf
I'm available by contract or FT, in the NYC metro area or via the 'Net.

Re: DC power versus AC power

[Scott Granados]

>
> Unnamed Administration sources reported that Scott Granados said:
> >
> > Is 48V DC at the amps present normallyin switch rooms etc enough to
cause
> > electricucian?  I have seen bad things with wrenches dropped across
> > batteries even 12 volt car batteries although in this case it was a
large
> > battery bank in a submarine but I was curious about the 48V sources in
> > switch rooms.
>
>
> Electrocution is but one way to die from too many columbs.
> Internal burning is a big one.  Most people die, not from immediate
> cardiac arrest, but rather from kidney/spleen/liver failure as
> they try to remove the cooked you parts from your bloodstream,
> and clog up. (First responder treatment is multiple saline inputs
> to flush you out, and keep flushing you. This via a friend who was
> "lit" and lived.)
>

The only way I've seen anyone die from being shocked is heart failure.  This
was a very very large AC hit though not DC.


> The instantaneous short circuit current available from a CO-grade
> battery string is nothing short of frightening. It will easily
> turn a 18" crescent wrench bright orange and start spitting the
> molten metal around within few seconds.
>
> I'm surprised you're still around after a sub battery accident.
> They're a grade up from most CO's in available current, I'd bet.
>

Yes, they are I don't recall the amps off hand but it was amazing.  It does
take a lot of juice though to spin motors that large and run all that
equipment considering your primary power source is nuclear also.

In my case I wasn't the one who was hit I was a fair distance off and
someone working, an electrician, touched a wrench across the terminals on
one cell only.  For get a few seconds pretty instantly the wrench was gone
as well as a better part of his hand and wrist.  However, touching both
terminals on the cell did not yield a shock which was what made me think and
ask the question i the first place.  I can't imagine the damage possible
though if someone in that setting touched one of the main bus's.

>
>
>
> --
> A host is a host from coast to [EMAIL PROTECTED]
> & no one will talk to a host that's close[v].(301) 56-LINUX
> Unless the host (that isn't close).pob 1433
> is busy, hung or dead20915-1433
>

Re: DC power versus AC power

[Michael Painter]

- Original Message -
From: "Scott Granados" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "nanog list" <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 3:40 PM
Subject: Re: DC power versus AC power


>
> Is 48V DC at the amps present normallyin switch rooms etc enough to cause
> electricucian?  I have seen bad things with wrenches dropped across
> batteries even 12 volt car batteries although in this case it was a large
> battery bank in a submarine but I was curious about the 48V sources in
> switch rooms.

I've laid across the buss-bars before...definitely an uneasy feeling, but never
felt it unless I was sweaty. 
 Capability of thousands of Amps, but it's the old "power transfer"
deal...internal resistance of the source vs. internal resistance of the load (your
body).

--Michael

>
>
>
> - Original Message -
> From: "David Lesher" <[EMAIL PROTECTED]>
> To: "nanog list" <[EMAIL PROTECTED]>
> Sent: Sunday, December 29, 2002 4:43 PM
> Subject: Re: DC power versus AC power
>
>
> >
> > Unnamed Administration sources reported that Michael Painter said:
> > >
> > >
> > >
> > > > >But, as Stephen already eluded to... Compared with an AC plant
> design, to
> > > me, one of the biggest drawbacks of a DC plant is safety  (I have had to
> > > kick a fellow worker away from the rack before). <<
> > >
> > > What was the worker doing?  Is this 48 VDC?
> >
> > Bet so.
> >
> > And note, it's not just ISP's, of course. I heard that Sprint
> > PCS ha[s,d] a Dallas tech in critical condition and a dead switch
> > after a dropped wrench & resulting fire.
> >
> > In the words of Phil Esterhaus:
> >
> > Let's be careful out there
> >
> >
> >
> >
> >
> > --
> > A host is a host from coast to [EMAIL PROTECTED]
> > & no one will talk to a host that's close[v].(301) 56-LINUX
> > Unless the host (that isn't close).pob 1433
> > is busy, hung or dead20915-1433
> >
>

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Charles Sprickman said:
 
> Additionally I wonder why non-conductive tools wouldn't be the norm in an
> environment where there's an "open" power grid? :)

"Fools rush in where."

It was in years past. I recall how excited the power room guys
were over TI's first all-plastic watches. They simply did not
ever wear same until then.



-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Scott Granados said:
> 
> Is 48V DC at the amps present normallyin switch rooms etc enough to cause
> electricucian?  I have seen bad things with wrenches dropped across
> batteries even 12 volt car batteries although in this case it was a large
> battery bank in a submarine but I was curious about the 48V sources in
> switch rooms.


Electrocution is but one way to die from too many columbs.
Internal burning is a big one.  Most people die, not from immediate
cardiac arrest, but rather from kidney/spleen/liver failure as
they try to remove the cooked you parts from your bloodstream,
and clog up. (First responder treatment is multiple saline inputs
to flush you out, and keep flushing you. This via a friend who was
"lit" and lived.)

The instantaneous short circuit current available from a CO-grade
battery string is nothing short of frightening. It will easily
turn a 18" crescent wrench bright orange and start spitting the
molten metal around within few seconds.

I'm surprised you're still around after a sub battery accident.
They're a grade up from most CO's in available current, I'd bet.




-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[Charles Sprickman]

On Sun, 29 Dec 2002, Scott Granados wrote:

> but I was curious about the 48V sources in switch rooms.

Don't forget there's a quiet yet resourceful list over at
[EMAIL PROTECTED]  They love talking about this kind of stuff.

Additionally I wonder why non-conductive tools wouldn't be the norm in an
environment where there's an "open" power grid? :)

Charles

>
>
> - Original Message -
> From: "David Lesher" <[EMAIL PROTECTED]>
> To: "nanog list" <[EMAIL PROTECTED]>
> Sent: Sunday, December 29, 2002 4:43 PM
> Subject: Re: DC power versus AC power
>
>
> >
> > Unnamed Administration sources reported that Michael Painter said:
> > >
> > >
> > >
> > > > >But, as Stephen already eluded to... Compared with an AC plant
> design, to
> > > me, one of the biggest drawbacks of a DC plant is safety  (I have had to
> > > kick a fellow worker away from the rack before). <<
> > >
> > > What was the worker doing?  Is this 48 VDC?
> >
> > Bet so.
> >
> > And note, it's not just ISP's, of course. I heard that Sprint
> > PCS ha[s,d] a Dallas tech in critical condition and a dead switch
> > after a dropped wrench & resulting fire.
> >
> > In the words of Phil Esterhaus:
> >
> > Let's be careful out there
> >
> >
> >
> >
> >
> > --
> > A host is a host from coast to [EMAIL PROTECTED]
> > & no one will talk to a host that's close[v].(301) 56-LINUX
> > Unless the host (that isn't close).pob 1433
> > is busy, hung or dead20915-1433
> >
>

Re: DC power versus AC power

[Scott Granados]

Is 48V DC at the amps present normallyin switch rooms etc enough to cause
electricucian?  I have seen bad things with wrenches dropped across
batteries even 12 volt car batteries although in this case it was a large
battery bank in a submarine but I was curious about the 48V sources in
switch rooms.



- Original Message -
From: "David Lesher" <[EMAIL PROTECTED]>
To: "nanog list" <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 4:43 PM
Subject: Re: DC power versus AC power


>
> Unnamed Administration sources reported that Michael Painter said:
> >
> >
> >
> > > >But, as Stephen already eluded to... Compared with an AC plant
design, to
> > me, one of the biggest drawbacks of a DC plant is safety  (I have had to
> > kick a fellow worker away from the rack before). <<
> >
> > What was the worker doing?  Is this 48 VDC?
>
> Bet so.
>
> And note, it's not just ISP's, of course. I heard that Sprint
> PCS ha[s,d] a Dallas tech in critical condition and a dead switch
> after a dropped wrench & resulting fire.
>
> In the words of Phil Esterhaus:
>
> Let's be careful out there
>
>
>
>
>
> --
> A host is a host from coast to [EMAIL PROTECTED]
> & no one will talk to a host that's close[v].(301) 56-LINUX
> Unless the host (that isn't close).pob 1433
> is busy, hung or dead20915-1433
>

Re: DC power versus AC power

[David Lesher]

Unnamed Administration sources reported that Michael Painter said:
> 
> 
> 
> > >But, as Stephen already eluded to... Compared with an AC plant design, to
> me, one of the biggest drawbacks of a DC plant is safety  (I have had to
> kick a fellow worker away from the rack before). <<
> 
> What was the worker doing?  Is this 48 VDC?

Bet so.

And note, it's not just ISP's, of course. I heard that Sprint
PCS ha[s,d] a Dallas tech in critical condition and a dead switch
after a dropped wrench & resulting fire.

In the words of Phil Esterhaus:

Let's be careful out there





-- 
A host is a host from coast to [EMAIL PROTECTED]
& no one will talk to a host that's close[v].(301) 56-LINUX
Unless the host (that isn't close).pob 1433
is busy, hung or dead20915-1433

Re: DC power versus AC power

[Michael Painter]

- Original Message - 
From: "Kuhtz, Christian" <[EMAIL PROTECTED]>
To: "Wayne Bogan" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 9:37 AM
Subject: RE: DC power versus AC power


> >But, as Stephen already eluded to... Compared with an AC plant design, to
me, one of the biggest drawbacks of a DC plant is safety  (I have had to
kick a fellow worker away from the rack before). <<

What was the worker doing?  Is this 48 VDC?

Thanks,

--Michael
 

Re: DC power versus AC power

[Måns Nilsson]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

- --On Sunday, December 29, 2002 00:46:56 -0500 [EMAIL PROTECTED] wrote:
> Does anyone actually wire up 
> both the A side and B side to a single DC power supply and use diodes to 
> keep the two supply grids separate?

We've built a number of "joiner" boxes in-house at KTHNOC; basically an
aluminium box with rectifier bridge and heatsink, and screw terminals. 

We use them for 2511 terminal servers and similar. So, yes. 

> DC also avoids bulky AC power cords...and not only are the wires less
> bulky, but you'll likely cut them to the actual length needed.  Since DC
> wiring is usually screwed down, they don't get bumped or accidentally
> pulled out of the outlets as often.

YMMV, but 4 times 2x10mm² + 16mm² PE (The DC connects for a 12n16 GSR) I
find bulkier than 4 10A power cords ;-). You are right on spot about the
tidy/sturdy part, though. 

- -- 
Måns NilssonSystems Specialist
+46 70 681 7204 KTHNOC  MN1334-RIPE

We're sysadmins. To us, data is a protocol-overhe
-BEGIN PGP SIGNATURE-
Version: GnuPG v1.0.7 (OpenBSD)

iD8DBQE+D2P802/pMZDM1cURAmCfAJ9lumFsIw0n1ZrUjWLg0/Fy1gC2/QCgm2/F
NvqZ52RiOzlYKY+ul2YF3lI=
=O9Am
-END PGP SIGNATURE-

RE: DC power versus AC power

[Kuhtz, Christian]

> Switched power supplies really don't care about the quality of the 
> sine  waves that feeds them, as long as they have energy to put into
> the "tank". On the other hand, video monitors like sine waves, and 
> they may not get along with DC inverters/rectifiers (or even portable
> AC no-breaks, which usually generates AC from DC).

Sure.  And not to get into a contest here, but it all depends on how bad the
approximation is and what gear it is we're talking about.  

It's just something to consider and research, and include in the decision.
Clean power plants (and that's got nothing to do with green ;) is always a
good thing.  Doesn't have to be perfect, just close enough for . 

Thanks,
Christian


*
"The information transmitted is intended only for the person or entity to
which it is addressed and may contain confidential, proprietary, and/or
privileged material.  Any review, retransmission, dissemination or other use
of, or taking of any action in reliance upon, this information by persons or
entities other than the intended recipient is prohibited.  If you received
this in error, please contact the sender and delete the material from all
computers."

Re: DC power versus AC power

[Rubens Kuhl Jr.]

| Not to mention additional cost of wasted electricity (which does add up
| significantly when it is anything but a spot solution) and pitfalls of
| inverters (like their imperfect sine waves).  And if you're putting spot
| solution UPS units out into the bottom of a particular rack, be ware their
| canny ability to catch fire when the price is right.

Switched power supplies really don't care about the quality of the sine
waves that feeds them, as long as they have energy to put into the "tank".
On the other hand, video monitors like sine waves, and they may not get
along with DC inverters/rectifiers (or even portable AC no-breaks, which
usually generates AC from DC).


Rubens Kuhl Jr.

RE: DC power versus AC power

[Kuhtz, Christian]

From: Wayne Bogan [mailto:[EMAIL PROTECTED]]
> For those AC only powered units, you can also purchase an invertor 
> for DC to AC conversion.  You would then have the advantages of DC
> for your AC equipment.  This does, however, add the potential of 
> another point of failure such as fuses or breakers in the invertor.

Not to mention additional cost of wasted electricity (which does add up
significantly when it is anything but a spot solution) and pitfalls of
inverters (like their imperfect sine waves).  And if you're putting spot
solution UPS units out into the bottom of a particular rack, be ware their
canny ability to catch fire when the price is right.

Inverters or rectifiers should be point solutions in a plant layout.  If you
have a lot of AC & DC, get two protected plants.  Only way to live.
Sometimes that's not just nice to have, but simply required.

If you're primarily a systems shop and have environmentally conditioned
space, get AC.  If you're in a nasty colo spot, with poor environmental
(read: not guaranteed meat locker climate 24x7), get DC & NEBS hardware or
hardware which meets NEBS almost entirely but doesn't carry the sticker for
some silly reason such as "easily flammable plastic used for front grill".
Depending on what your colo requires.  There are many different flavors of
colo. 

Speaking of flavors, consider the impact of a turf vendor based on whatever
decision you chose when going into colo space.  May or may not be an issue.

See what equipment offers what, do the math on cost of plant and gear, pros
& cons.  And make a business decision based on engineering data. (uh, right)

But, as Stephen already eluded to... Compared with an AC plant design, to
me, one of the biggest drawbacks of a DC plant is safety  (I have had to
kick a fellow worker away from the rack before).  One of the biggest
advantages is simplicity of design when it comes to battery plant.  

There is no universal answer, it all depends.  And one ends up shuffling off
and having to do a bunch of homework.

Of course, this is all IMHO and I've been wrong before.

Thanks,
Christian


-Original Message-
From: Wayne Bogan [mailto:[EMAIL PROTECTED]]
Sent: Sunday, December 29, 2002 1:06 PM
To: [EMAIL PROTECTED]
Subject: Re: DC power versus AC power




- Original Message -
From: "Stephen Sprunk" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 1:58 AM
Subject: Re: DC power versus AC power


>
> Thus spake ip dude <[EMAIL PROTECTED]>:
> > Hello NANOG group. I am trying to make a case for using DC power
> > supplies versus AC power supplies for typical IP networking
> > equipment. Is there any published whitepapers detailing this subject?
> > Do you have any suggestions to aide my argument?
>
> Most of the argument depends on the facility you're in.  Assuming you're
> asking as an end-customer:
>
> DC requires clue from your staff when installing/removing equipment, and
> this means safety training at a minimum.  Power choice also affects your
> equipment purchasing: DC versions of gear are often priced higher, and
gear
> not intended for telcos/ISPs may not have a DC option available at all.
>
> OTOH, many colos -- especially ones run by telcos -- don't provide AC UPS.
> If you want AC UPS in these environments, you'll have to provide your own,
> which is expensive, bulky, and a maintainance burden.
>
> If you're building your own datacenter, please specify that and I'm sure
> you'll get a whole different discussion :)
>
> S
>
>



*
"The information transmitted is intended only for the person or entity to
which it is addressed and may contain confidential, proprietary, and/or
privileged material.  Any review, retransmission, dissemination or other use
of, or taking of any action in reliance upon, this information by persons or
entities other than the intended recipient is prohibited.  If you received
this in error, please contact the sender and delete the material from all
computers."

Re: DC power versus AC power

[Wayne Bogan]

For those AC only powered units, you can also purchase an invertor for DC to
AC conversion.  You would then have the advantages of DC for your AC
equipment.  This does, however, add the potential of another point of
failure such as fuses or breakers in the invertor.


- Original Message -
From: "Stephen Sprunk" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Sunday, December 29, 2002 1:58 AM
Subject: Re: DC power versus AC power


>
> Thus spake ip dude <[EMAIL PROTECTED]>:
> > Hello NANOG group. I am trying to make a case for using DC power
> > supplies versus AC power supplies for typical IP networking
> > equipment. Is there any published whitepapers detailing this subject?
> > Do you have any suggestions to aide my argument?
>
> Most of the argument depends on the facility you're in.  Assuming you're
> asking as an end-customer:
>
> DC requires clue from your staff when installing/removing equipment, and
> this means safety training at a minimum.  Power choice also affects your
> equipment purchasing: DC versions of gear are often priced higher, and
gear
> not intended for telcos/ISPs may not have a DC option available at all.
>
> OTOH, many colos -- especially ones run by telcos -- don't provide AC UPS.
> If you want AC UPS in these environments, you'll have to provide your own,
> which is expensive, bulky, and a maintainance burden.
>
> If you're building your own datacenter, please specify that and I'm sure
> you'll get a whole different discussion :)
>
> S
>
>

Re: DC power versus AC power

[Stephen Sprunk]

Thus spake ip dude <[EMAIL PROTECTED]>:
> Hello NANOG group. I am trying to make a case for using DC power
> supplies versus AC power supplies for typical IP networking
> equipment. Is there any published whitepapers detailing this subject?
> Do you have any suggestions to aide my argument?

Most of the argument depends on the facility you're in.  Assuming you're
asking as an end-customer:

DC requires clue from your staff when installing/removing equipment, and
this means safety training at a minimum.  Power choice also affects your
equipment purchasing: DC versions of gear are often priced higher, and gear
not intended for telcos/ISPs may not have a DC option available at all.

OTOH, many colos -- especially ones run by telcos -- don't provide AC UPS.
If you want AC UPS in these environments, you'll have to provide your own,
which is expensive, bulky, and a maintainance burden.

If you're building your own datacenter, please specify that and I'm sure
you'll get a whole different discussion :)

S

Re: DC power versus AC power

[jlewis]

On Fri, 27 Dec 2002, Scott Granados wrote:

> It is likely that in many settings during power failures transition from ac
> street power to ac generator power will have some lag and during that time
> your hardware could loose power.  This of course depends on ups systems in
> use and many factors.  Dc usually however is clean in its transition and
> goes with out saying is battery backed up.

I'll add to that, that since DC removes the need for your own UPS's, by
going with DC, you save rack space, deploy less gear (UPS's are HEAVY),
and don't have to worry about which POPs have how many UPS's with dead
batteries at any given time.  OTOH, since with DC you're unlikely to have
any backup power of your own, it is important to wire up both an A side
and B side.  Some places (like certain telcos) like to briefly turn off
parts of their DC power grids somewhat regularly.  This makes gear with
only one set of DC inputs rather annoying.  Does anyone actually wire up 
both the A side and B side to a single DC power supply and use diodes to 
keep the two supply grids separate?

DC also avoids bulky AC power cords...and not only are the wires less
bulky, but you'll likely cut them to the actual length needed.  Since DC
wiring is usually screwed down, they don't get bumped or accidentally
pulled out of the outlets as often.

--
 Jon Lewis *[EMAIL PROTECTED]*|  I route
 System Administrator|  therefore you are
 Atlantic Net|  
_ http://www.lewis.org/~jlewis/pgp for PGP public key_

Re: DC power versus AC power

[Scott Granados]

It is likely that in many settings during power failures transition from ac
street power to ac generator power will have some lag and during that time
your hardware could loose power.  This of course depends on ups systems in
use and many factors.  Dc usually however is clean in its transition and
goes with out saying is battery backed up.  Also, some hardware only is
available in DC form such as the ons15454's I believe.


- Original Message -
From: "ip dude" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, December 27, 2002 5:14 PM
Subject: DC power versus AC power


>
> Hello NANOG group. I am trying to make a case for using DC power supplies
versus AC power supplies for typical IP networking equipment. Is there any
published whitepapers detailing this subject? Do you have any suggestions to
aide my argument?
>
> _
> Get your own free Ranch eMail and Classified Ads at http://cattletoday.com
>
> _
> Select your own custom email address for FREE! Get [EMAIL PROTECTED] w/No
Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag
>

DC power versus AC power

[ip dude]

Hello NANOG group. I am trying to make a case for using DC power supplies versus AC 
power supplies for typical IP networking equipment. Is there any published whitepapers 
detailing this subject? Do you have any suggestions to aide my argument? 

_
Get your own free Ranch eMail and Classified Ads at http://cattletoday.com

_
Select your own custom email address for FREE! Get [EMAIL PROTECTED] w/No Ads, 6MB, 
POP & more! http://www.everyone.net/selectmail?campaign=tag