bud-- wrote:
On Nov 23, 9:56 am, "w_tom" wrote:

There is no stopping or blocking of lightning as plug-in protector
manufacturers hope you believe.
The best information I have seen on surges and surge protection is at
http://www.mikeholt.com/files/PDF/Li...ion_May051.pdf
- the title is "How to protect your house and its contents from
lightning: IEEE guide for surge protection of equipment connected to AC
power and communication circuits" published by the IEEE in 2005 (the
IEEE is the dominant organization of electrical and electronic
engineers in the US).

A second guide is
http://www.nist.gov/public_affairs/p.../surgesfnl.pdf
- this is the "NIST recommended practice guide: Surges Happen!: how to
protect the appliances in your home" published by the National
Institute of Standards and Technology (the US government agency
formerly called the National Bureau of Standards) in 2001

Both guides were intended for wide distribution to the general public
to explain surges and how to protect against them. The IEEE guide was
targeted at people who have some (not much) technical background.

Both say plug-in surge suppressors are effective.

All interconnected devices, like a computer and printer, need to
connect to the same surge protector. If a device, like a computer, has
external connections like phone or LAN, all those wires have to run
through the surge suppressor for protection. This type of suppressor is
called a surge reference equalizer (SRE) by the IEEE (also described by
the NIST). The voltage on all wires connected to the SRE (power, phone,
CATV, LAN, ...) are clamped to a common ground at the SRE and the
voltages are held to a value that is safe to the connected device.
Ratings vary from junk to very high.

While a single point ground with phone, CATV, ... protectors connecting
with short wires to the grounding electrode wire at the power service
is best for eliminating the ground potential differences in Doug's
post, SREs also provide protection.


That protector also does not stop or absorb anything. A protector is
only as effective as its earth ground. Effective protectors make a
short and temporary connection to earth.
As is clearly described in the IEEE guide, plug-in suppressors work by
clamping,.They do not work primarily by earthing, or stopping,
blocking, absorbing.


Many
believe a plug-in protector will somehow stop or absorb what 3 miles of
sky could not.
Among those who believe that are the IEEE and NIST.

I suggest that you go back and re-read your references. For instance,
on pg. 38:

Well-designed and well-built plug-in protectors will actually withstand
the
10,000 A (8x20 µs) surge current, and that is rating required by NFPA
780-2004
for plug-in protectors. However, the UL 1449 Standard only requires
plug-in
protectors to withstand, without damage, ~20 500 A surges. Inexpensive
protectors using the 6C type of circuit are designed to respond to
overload by
opening the protective fusing shown in Figure 6C, sometimes at surge
currents
barely over the 500 A limit. Because the UL 500 A surge withstand
requirements
are relatively weak, it is important to have both a hard-wired
protector at the
service entrance and a plug-in protector at the critical loads.

This clearly recommends that you don't depend upon a surge protector
alone, simply because the minimum UL requirements are REALLY a minimum.
Most people don't know that surge protectors use devices (MOVs) that
have a limited life, and they don't have a visible indicator showing
how much of their life is left. High quality surge protectors are sold
by www.zerosurge.com.

The IEEE report confirms what w_tom was saying about voltage
differentials on the building grounding during a lightning strike:

If wiring comes into a building at many different points, it is much
more difficult
to get proper protection against lightning surges. Even if surge
protectors are
installed at these alternate entry points, the long ground wires
running back to the
main building ground greatly reduce the effectiveness of the
protectors. In highlightning
areas, where lightning protection is a major concern, it is worth
routing
as many AC and signal cables as possible past the building power entry
point, to
facilitate good grounding for protectors and cable sheaths

I highly recommend a thorough reading of the IEEE document for a
complete discussion of this issue. The take home message: individual
surge protection devices ARE NOT a complete lightning protection plan.

Tom Seim
Richland, WA