Re: Backups

Bud-- wrote:

Both the IEEE and NIST guides say plug-in suppressors are effective. The
same protection may or may not be built into a UPS. Or a UPS can be
plugged into a plug-in surge suppressor. In the US, a UPS with surge
protection should be listed under UL1449. Plug-in suppressors, have MOVs
between H-N, H-G, N-G  - they protect against all surge modes.

For many years I did work for a small company that installed monitoring
equipment for utility companies. Much of the monitoring equipment was
either installed or had sensors atop water towers and on bridges, so you
can imagine the lightening problems we had on those wonderful metal
structures. We never found a completely satisfactory setup and I have
opened many, many carbonized surge protection devices. The most effective
ones were for power leads. One especially good one used either MOVs or gas
discharge tubes, depending on the model and application, in front of heavy
inductors (#10 wire coils) with dedicated grounds of at least #6 wire. In
very high risk areas of the Southeast US, we would actually filter the
power main at the service entrance then add additional devices at the
connection point for clusters of equipment. We lost a number of filters
but only 2-3 computers or pieces of equipment over the years but when
lightning makes a direct strike on the service box all you can do is adopt
the old pilot's maneuver of last resort: Bend over, put head between legs,
kiss a$$ goodbye.

The approach we used to prevent surge damage - which was far more common in
industrial settings - was to power equipment with battery backup units
which ALWAYS supplied power via the inverter. These use either the power
line or the battery to power the inverter so that nothing is ever passed
directly to the protected equipment. We rarely had any issue at all with
power-induced failures that way.

Telephone lines, network cables, and instrumentation leads are a totally
different problem. These will pick up spikes via induction from nearby
events and they are hard (expensive) to protect without affecting the
signal you want from circuit, especially instrumentation lines. Optical
isolators are about the best you can do but even that provides coupling
paths via power supplies and such.

Over the years, I have found that the biggest single problem with protection
schemes has been the quality of the grounding system. Being so simple, we
rarely pay attention to it once installed. Any connections in the ground
system need to be inspected at regular for intervals for corrosion and
continuity. Clean or tighten connectors, etc. That applies for both
lightning as well as surge systems. I worked mainly with industrial
locations, but you would be surprised at what a hair drier or electric
drill can do to your power lines!

--
Will Honea
.

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