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Power companies sometimes include as bill-stuffers the suggestion to
disconnect your appliances when a severe lightning storm is approaching.
But that is no help if you are not in the house at that time. If, on the
other hand, you are in the house, pulling out the power cord of an
appliance that remains connected to a telephone line or cable
TV might not be the best idea: you would lose the grounding
of the appliance normally done by the power cord -
possibly a safety problem should a surge come
upon the telephone or cable TV.

By showing you the basic principles of surge protection, this booklet should
help you make the choices that fit your needs for protection, without
overdoing it. To make the right choice, it is useful to note that there
are two types of electronic appliances. For each of these types, a
different type of surge protector might be needed. These
types include:
¨ Simple, one link connection to power the system
¨ Dual connection to both power and communications

One-link connections
Examples of one-link connection of powered electronic appliances include a TV
set with "rabbit ears" antenna, a portable radio receiver, a computer with no
modem connection or remote printer, a compact fluorescent lamp, etc. In
the category of one-link connection we also find an old-fashioned
telephone connected only to the telephone system.

Note that most of these have a two-prong
plug, which is their sole connection to the
power system. For the TV set, a simple
AC plug-in surge protector on the power
cord would be sufficient. For just the
lamp, the cost of a surge protector
would be greater than the cost of
simply replacing the lamp, if damaged
by a surge - and therefore not be justified.
¨What kind of appliances ?

Two-link connections
This type of appliance is another matter. Typical of these would be a computer
with a modem, a video system with cable or satellite link, a phone system
directly powered from a receptacle (those with a large adapter plug
and a thin cable with jack which goes to the appliance generally
have sufficient internal isolation against surges).

The surge problem with this type of appliance is that a surge
coming in from one of the two systems - power or
communications - can damage the appliance, because
of a difference in the voltage between the two
systems when the surge occurs. This can
happen even when there are surge
protectors on each of the systems.
(For those of you interested in
finding out why that is so, more on
that subject on page 18.)
Fortunately, you can find a special type of surge protector
against the problem, as described next.

Equalizing differences
A simple solution to the problem of voltage differences for two-link
appliances is to install a special surge protector that incorporates, in the
same package, a combination of input/output connections for the two
systems. Each link, power and communications, is fed through the
protector which is then inserted between the wall receptacles and
the input of the appliance to be protected. This type of surge
protector is readily available in computer and electronics
stores, and the electrical section of home building stores.

In addition to words on the package, it can be recognized
by the presence of either a pair of telephone jacks or
video coax connectors in addition to the power
receptacles. Some models might have all three in
the same package. Do note a few words of caution:
(1) Read carefully the instructions or markings to
find which is "in" and which is "out" for the
telephone wires. It is important to note, before you
buy the product, whether your wall receptacles are
wired for three-prong power cords. Some of these
combined protectors might not work very well if
plugged into a 2-blade receptacle, using a "cheater"
plug. (On some, an indicating light will signal that.)

Not just power-line surges

Among other disturbances on the power lines, there was a brief mention of
sags and outages on page 2. You are certainly and unhappily well-
acquainted with outages that can occur for any number of reasons
beyond the control of your utility. Sags - a brief decrease of the line
voltage - can be more subtle and do occur more often than the
complete outage. You will notice these when the lights dim
momentarily, digital clocks or VCR controls blink, or your
computer shuts down then reboots - possibly losing some

Industrial and commercial users, health-care facilities and other critical
systems have for many years used a device called "uninterruptible
power supply" (UPS) that provides continuous power across a sag,
or for the first portion of an extended outage (an independent
local power generator set can then kick in).

The aggravation of consumers caused by sags and outages has created a
mass-market for consumer applications, making them affordable when
looked at as protection against these annoying (but not damaging)
disturbances - and with built-in surge protection as a bonus in many
cases. These consumer-type UPSs have a small battery which is
sufficient to ride through any sag and short outages. Some
models even include the software to make a computer shut
down in an orderly sequence in case of a long outage.

Surges in other systems
So far, we have looked at surges on the power line alone, or on a combination
of power and communications lines. Surges of a slightly different kind can
also happen in parts of other electrical systems that do not directly
involve a power line. Examples of these are: the antenna for a
remote garage door opener, the sensor wiring for an intrusion
alarm system, the video signal part of a satellite dish receiver.
Surges in these systems are caused by nearby lightning

These other systems just mentioned have not been the subject of standards
on surge protection as much as power and telephone systems.
Furthermore, protective devices for these other systems are not as
readily available to consumers. It is more difficult to offer well-defined
guidance on surge protection for these systems. Applying
preventive surge protection schemes to an existing system
might be difficult when the sensitivity of such a system to
surges is not known. When considering installation of a
new system, it would be a good idea to ask pointed
questions on that subject before signing the contract.

¨Protection for other systems

Some codes or practices aimed at providing safety for persons, when they are
correctly applied, can also provide some equipment protection.

For instance, the general practice of telephone companies is to provide a
surge protector as part of their services at the point where the telephone
line enters the house (in dense urban environments, the National
Electrical Code allows an exception). This protector is known as the
"Network Interface Device" (NID) and you will find it on the outside
of your house (see the drawing on page 19).

Another example of code requirement is that of cable TV systems for which
the National Electrical Code requires proper safety-oriented grounding
practices. The problem, however, is that in some cases, the video
equipment can still be damaged by voltage differences, as explained
on page 12.

With the increasing popularity of small-dish
satellite receivers, installation by the user as
do-it-yourself has also increased. Typical
instructions for installation show how to
make the connections, for instance in the
figure at right. What the figure does not
show is the need to provide a combined
protector for power, telephone, and cable.

A well pump installed outside the house presents a
double challenge: protecting the pump motor itself
against surges, and protecting the house wiring
against surges that might enter the house by the
line that powers the pump. The first protection is
generally built-in for modern submersible pumps.
The second protection should be provided by a surge protector installed at the
point where the power line to the pump leaves the house, using protectors
similar to those applied at the power line service entrance.

Intruder alarm systems using wires between sensors and their central control
unit can be disturbed - and damaged in severe cases - by lightning
striking close to the house. The wires necessary for this type of
installation extend to all points of the house and act as an antenna
system that collects energy from the field generated by the
lightning strike, and protection should be included in the
design of the system, rather than added later by the
owner. Wireless systems are less sensitive than
wired systems.

Questions .... and answers

Among the questions often asked by consumers about surges, here is a
selection of typical concerns and simple answers.

Q - When looking at the devices offered in the store, the packages show
specifications and claims that puzzle me. Can you explain ?
A's - Here are some typical specifications, and corresponding comments:
Joules - A (simplified) measure of the surge energy that the protector can dissipate without
damage to itself. The higher the value, the more energy the protector can handle. Typical
values range from about 100 joules, up to 1000 joules or more. Because this joule
number is often based on the three combinations of the wiring, many specifications
show the total joules rather than a breakdown among each of the three
combinations. Maximum surge current (below) may give better information.
Clamping voltage - A measure of the voltage-limiting capability of the protector. An
oversimplified perception might be that the lower, the better. Many specifications show
330 volts for this voltage. This number is embedded in the UL standard values, but it is
not a requirement. Somewhat higher clamping voltages, such as 400 volts or more,
may be sufficient for protecting electronic appliances, and will make the surge
protector itself less susceptible to damage from "swells" (see page 2).
Maximum surge current - A measure of the ability of the protector to handle surge current
without damage to itself. You will find a range of values from several hundred to several
thousand amperes. Even the lower values offered by manufacturers are sufficient for
most surges, but a higher value will give you (generally for a slightly higher price)
a comfortable margin of peace of mind.
Speed of response - This specification appears on some packages, others do not even
mention it. Since practically all protectors use the same kind of technology for the
protective components, and their speed of response is inherently adequate for power-
line surges, there is no need to emphasize a fast speed of response.
Internal protection - Some packages provide a description of what happens on the load side
of the surge protector (cut-off or still powered), should the protective element be damaged
by an exceptionally large surge or a long overvoltage. See on page 7 your choice, "Quit
and be protected or continue" - but now unprotected. Some packages also provide
a cut-off and reset feature in cases of large swells, protecting the protector itself
as well as the load.
Indicating lights - See the discussion of their meaning on page 7. Be sure that you will
remember the meaning after you have discarded the package. If a card with
explanations is included in the package, save it because the meaning of the light -
on or off, and what the difference there is among colors - is not always clear on
the device itself. If the protector maintains power on the load side, how often
will you look under or behind your desk to check and make sure that the
"Protection on" light is still on ?
UL 1449 Second Edition - Some packages show “UL listed Second Edition” rather than the
simple "UL Listed" found on others. It shows explicitly that the product has passed the
most recent, improved tests for safety. Other standard symbols such as ETL or CSA
might be present instead of UL. They all represent the latest testing for safety.
Guaranteed protection - A measure of the manufacturer's confidence in the actual
performance of the product. As for all guarantees, do read the fine print.

¨More questions and answers

Q - If I install one plug-in surge protector in one room, are the receptacles in other
rooms also protected ?
A - Yes, but only to some degree. The wiring in your house is split into several "branch
circuits" originating from your service entrance panel. If a surge protector is installed
on a particular branch circuit, the other receptacles on the same branch circuit
might benefit from it, but that benefit is much less on other branch circuits. To
be more relaxed about protection in other rooms, it would be a good idea
to install a surge protector for each of the sensitive appliances in the
house. This is especially true for the multi-link appliances because
of the problem explained on page 12. (See the next Q&A on
whole-house protection and Figure 3 on page 19.)
Q - Will a surge protector installed at the service entrance be sufficient for the
whole house ?
A - There are two answers to that question: Yes for one-link appliances, No for two-link
appliances. Since most homes today have some kind of two-link appliances, the
prudent answer to the question would be No - but that does not mean that a surge
protector installed at the service entrance is useless. An important function of the
service-entrance protector is to divert large surges coming on the power line,


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