any good UPS for a Fedora server

[Mikkel L. Ellertson]

John Summerfield wrote:
> 
> In the event of a quake, it seems to me prudent to cut HT and mains, but
> then generator sets automatically starting up would tend to negate the
> action.
> 
Not really - before you cut the mains, you switch the generator set
control to off instead of auto. The transfer switch and remote
generator controls are normally located right by the mains - it
makes the wiring so much easier. It can get more complicated in data
centers, or large buildings where only specific sections are
connected to backup power. (Things like elevators and emergency
lighting...) But they are also not unattended installations.

> I occasionally hear about events involving live wires on the ground
> following accidents and fires. It's bad news, especially for the poor
> kid that picks one up.
> 
This should not be a problem with even a home generator setup. This
is because any setup should disconnect from the incoming line while
using the generator. (A setup for a farm, or designed to power
several buildings is different. You can have overhead lines between
the generator and different buildings.) You need to do this not just
for safety sake, but because if you don't, you will overload your
generator because you are trying to power your neighbors as well.
Any auto-start setup that does not include a transfer switch to
automatically take care of this was designed/installed by an fool.
For that matter, even manual-start setups should have it. The
practice some people use with a double-mail cord to connect the
generator to the house wiring after pulling the mains is not a safe
practice.

I have installed a few backup generator setups over the years,
especially in preparation for y2k. The risk from a proper
installation in not significantly greater then when you are powered
off the mains. The main added risk is that fact that you are running
some kind of engine to power the generator, and it has some type of
fuel system. This is slightly less risky then running a car engine.
(It is not moving, and the fuel tank/lines are normally better
protected.) If your generator runs off of propane/natural gas, then
the added risk is probably less. You would probably have that fuel
source on location anyway.

Now, what is scary are the battery banks used to power a large UPS
installation. I have seen too many installations where there is no
short-circuit protection on the battery leads. When you have a bank
that produces 120V, and has the short-circuit potential of several
thousand amps, the results of a short can be interesting. Then
again, they will usually vaporise enough copper to clear the short.
But the plasma created while doing so tends to be hard on the rest
of the equipment located there. There is a fair amount of heat, as
well as light and RF generated when you vaporise a few cubic inches
of copper. (I have seen 6" of 1/4" x 6" copper bus missing.)

A setup with a couple of 12V deep discharge batteries and an
inverter is dangerous on a lower scale. But it does have an added
danger that is often overlooked when it is a home-brew setup. When
you charge the batteries, the produce hydrogen gas, and that is
explosive. If you do not have proper ventilation, you risk an
explosion. The biggest danger is when charging after heavy use, but
even normal maintenance charging produces some. This is why you have
to add water every so often - it gets broken down as a byproduct of
charging.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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