"w_tom" wrote in message
...
Was UPS between AC mains and computer? No.

Wrong. Topologically the UPS is "between".

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.


WRONG! About a critical 10 nanoseconds WRONG nevermind the impedances and
common mode condiderations!

Any transient from the
receptacle confronts UPS and computer equally.

Not in the critical time domain.

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.

NO, the first component with surge suppression topologically is usually the
one that takes the HIT. Do you suppose that's by design?

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.


OH, you mean unless the building is a heavily constructed Faraday cage and
all wiring has feedthru bypass and surge suppression, then a destructive
transient could get through and that has NOTHING to do with you high
transient impedance ground wire.. Why is it that we all knew that?

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.

HUH, frequently good surge protectors are destroyed by big surges just as
they are designed to do. The good one FAIL closed circuit where protection
is even better!

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,

NO, a large server farm has grid ground and power grid firewalls.

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

No, you are getting closer to reality.

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.

To a good Faraday cage or ground plane. A circuit of LOW AC IMPEDANCE.

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.

What that all boils down to is design the Faraday Cage or ground plane well
and has little to do with actual earth grounding save the UL and electrical
code.