Was UPS between AC mains and computer? No. UPS and
computer both connect to AC mains just like light bulbs. In
fact it would be same protection if both computer and UPS
shared same wall receptacle. Any transient from the
receptacle confronts UPS and computer equally. However
protection inside a UPS is often so grossly undersized that a
surge too small to damage a computer might still damage the
UPS. Furthermore, some computers can even act as surge
protectors - shunt a destructive surge so that it does not
seek earth ground via other computers.

Until you define specific circuits - including how every
wall receptacle is wired, then I cannot provide more
information.

I cannot say exactly why that particular event happened.
But above is one reason why a UPS may be damaged and computer
is not. Computer power supplies have internal protection.
Protection so sufficient that there is little adjacent to a
power supply that can enhance protection. But computer
internal protection can be overwhelmed if destructive
transients are not earthed before entering the building.

Bottom line is this. You had UPS failure. Therefore you
have no effective surge protection. Even surge protectors
must not be damaged due to a surge.

To provide a better answer, do as I do - autopsy the dead
body. Replace the defective part to learn what has actually
been damaged. Autopsy only complete when the failed unit is
fully functional.

If a server farm has no 'whole house' protection and a single
point earth ground, then no UPS or plug-in protector is going
to do anything better. In fact, it is just not a reliable
operation if 1) every incoming utility line does not enter at
the common service entrance all connected to the single point
earth ground and 2) building does not have necessary 'whole
house' protector on incoming AC mains. From Sun Microsystems
planning guide:
http://www.sun.com/servers/white-pap...ning-guide.pdf
Lightning surges cannot be stopped, but they can be diverted.
The plans for the data center should be thoroughly reviewed
to identify any paths for surge entry into the data center.
Surge arrestors can be designed into the system to help
mitigate the potential for lightning damage within the data
center. These should divert the power of the surge by
providing a path to ground for the surge energy. Protection
should be placed on both the primary and secondary side of
the service transformer. It is also necessary to protect
against surges through the communications lines. The
specific design of the lightning protection system for the
data center will be dependent on the design of the building
and utilities and existing protection measures.

If you are suffering transient damage, then the human is
reason for failure. What Sun writes is so well proven and
understood that it was standard even before WWII. Protection
is only as effective as its earth ground.

As for your brownouts - if any voltage is too low for a
computer, then the utility has grossly violated national
standards. A PUC call would create a massive response - if
your AC voltage drops so low as to be problematic to a
computer.

someone wrote:
"w_tom" wrote in message
...
A 3 or 5% reduction in voltage, also known as a brownout to
the utility, is totally irrelevant to electronics and
especially irrelevant to computers. A computer works just
fine even when incandescent bulbs dim to less than 40%
intensity. Even demanded in Intel specifications. IOW what
the utility calls a voltage reduction is full power to the
computer. Utility would have to decrease voltage more than
20% for a computer to see a brownout. But if utility voltage
drops that low, then electric motors may be damaged. IOW
voltage too low to damage electric motors is even full power
to a computer - which demonstrates how resilient a computer
really is.

BTW, utility does not institute a voltage reduction to save
money. Voltage reductions are a last ditch effort to avoid
rolling blackouts.

True - my opinion as well - perhaps you could convince my
local utility re this procedure being used on a daily basis.

Spikes and harmonics are (or should be) irrelevant to a
computer. Again, because the computer is so resilient.
However that internal computer protection assumes the building
has a 'whole house' protector so that spikes cannot overwhelm
computer internal protection.

All of which is irrelevant to HD protection. Either the
power supply will output correct power or it will shutdown.
This, of course, assumes the computer assembler had basic
electrical knowledge and did not install those 'defective by
design' $25 or $40 power supplies. But again, this was
explained earlier.

There is nothing cost effective adjacent to the computer. No
UPS nor power strip protector that will protect computer
hardware. Computer internal protection assumes the building
has implemented a 'whole house' protector on AC mains
connected less than 10 feet to central earth ground.
Protection as it was even done and well proven before WWII.

Perhaps you could explain the half dozen UPS I have seen
that operated correctly and interrupted close in electrical
faults. Naturally the UPS were scrap after the electrical
event - but the protected electronics were ok. $40 UPS vs
$800 desktop or in one situation $200 - $300 UPS vs. $5000
of servers.