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practice guide
recommended
NIST




Special
Publication
960-6
ABOUT THIS BOOKLET ....

This booklet has been prepared to help home dwellers, owners,
contractors, insurance agents and all parties interested in reducing
the number of cases and severity of equipment damage caused
by the unavoidable surges that occur in the electrical systems.
It is offered as a public service without any commercial
intentions.

The information offered here is the result of collective efforts by several
experts on the subject, but presented in a simple format with practical
hints on what to avoid and what to do. General principles are
explained, but specific brand names are not discussed or
mentioned as the technology and packaging techniques
are constantly evolving.

n The need for protection – What is a “surge”
n A few words about other power problems
n Source of surges – Lightning and other
n How tough are today’s appliances
n Protection for the whole house
n Protection at the outlet
n Good and bad installations
n Where and how to get help
n Common questions and answers
n A few hints for your electrical contractor
HOW TO PROTECT THE APPLIANCES
IN YOUR HOME
What's a surge ?
The power you get from the wall outlet is known as "120
volts AC power." It can be represented by a sine wave
of voltage, as shown at the bottom of this page. The
power companies try to keep that voltage
uniform. Lightning, short-circuits, poles
knocked down by cars, or some other
accident can make the voltage jump to
hundreds, even thousands of volts.

The voltage spike shown on the left of this page is what
engineers call a "surge." A surge will last only a few
millionths of one second (the "blink of an eye" is
thousands of times longer than the typical
surge). It is enough to destroy or to
upset your appliances.

What can a surge do
to your appliances ?
Your appliances are designed to run on the normal 120 volts AC
supply, with some tolerance for more or less, but they can be
damaged, or their controls can be upset by surges. The
result is then frustration and repair bills, and even a fire in
rare cases.

See the next pages for a discussion of how sensitive
your appliances can be to these surges.




Don't give up !
You can do something about it, your electrician can help
and even the power company can offer help, as this
booklet will show you - the why’s and how’s.
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¨ Other disturbances . . .

.... and what they can do to your appliances
In the normal operation of a power system, unavoidable disturbances
other than surges also happen. They can upset electronic appliances,
but are unlikely to cause permanent damage. This booklet is
concerned with surges and how to protect your appliances
against surges. However, just to give you an idea of what
these other disturbances can be, the graphs and words
below will give you the right words when you want to
discuss a problem with your power company, your
electrician, and (hopefully, not any longer) an
electronics repair shop.

This is the voltage that we all take for
granted, every second of the minute,
every minute of the hour, every hour of
the day, every day of the year. But
occasionally, for a short time ....
Normal line voltage
The voltage falls below normal: a sag.
Sags are unlikely to damage most
appliances, but they can make a
computer crash, confuse some
digital clocks and cause VCRs to
forget their settings.
Sag
The reverse of a sag is called a swell:
a short duration increase in the line
voltage. This disturbance might
upset sensitive appliances, and
damage them if it is a very large
or very long swell.
Swell

Noise is a catch word sometimes used
to describe very small and persistent
disturbances. These do not have
damaging effects but can be a
nuisance.
Noise
There is, of course, the ultimate disturbance: an outage - no voltage at all !

These disturbances are different from surges, but they should be
mentioned because the remedies are generally different. As we will
see later, some available devices can help overcome both.




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¨
Sensitive appliances in your home

Your home contains all sorts, types or kinds of appliances. By "appliances,"
understand not only the traditional household helpers, but also the
entertainment electronics, the family's computer(s), smart telephones,
control systems (thermostats, garage door, etc.), and all the new things
to come.




More and more, traditional large
appliances in your home depend on
very sophisticated electronics for
their control. This can often make
them sensitive to surges (as well
as power interruptions, but that is
another story ...).

To help sort out which types of your appliances might be damaged or upset,
you can describe them in general terms depending on their connections:
power, telephone, cable, or antennas. Each of these connections offers
a path for a surge to come in, something that might be overlooked
when the cause of damage is explained as a "power surge."

The first type includes electronics that are connected only to the power, such
as a computer with no modem, a TV set with rabbit ears, a VCR not
connected to cable TV, a table-top radio, a microwave oven, etc. Surge
protection of these is not particularly difficult, and quite often it is
already built-in by the manufacturer.

The second type, for which more protection might be needed, includes
electronics that are powered, of course, from your power receptacles but
also connected to an external communications system: telephone, cable
TV, satellite receiver. A slightly different but similar situation, which
also needs attention, is that of appliances connected to a household
control system such as garage door opener, intrusion or fire alarm,
automatic sprinklers, or intercom.

We will see later why the two kinds of appliances face different risks of
being damaged and consequently might require different protection
methods.
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¨Where do surges come from?

There are two origins for the surges that occur in your power system: lightning
surges and switching surges. A few words about these will help you better
understand what can be done to protect against them, and make good decisions
on risks versus economics.

Lightning surges, occur when a lightning bolt strikes between a cloud and objects
on earth. The effect can be direct - injection
of the lightning current into the object, or
indirect - inducing a voltage into electrical
circuits.
From
Nature’s
We will look at ways of protecting your
wrath . .
appliances against lightning surges that
come by way of the wires - power,
telephone, cable, etc. Protection of the
house against the direct effects of
lightning is done by properly grounded
... to Mother’s lightning rods, a job to be done by
gentle touch professionals . Note also that lightning
rods are intended to protect the structure
of the house and avoid fires. They do not
prevent surges from happening in the
wiring.

Direct lightning effects are limited to the object being struck and its
surroundings, so that the occurrence is considered rare but it is nearly
always deadly for persons or for trees. Well-protected electrical systems
can survive a direct strike, perhaps with some momentary disturbances
from which they recover (blinking lights and computers restarting
during a lightning storm). The key word, of course, is "well-protected"
and that is why this booklet is offered to help your home have a well-
protected electrical system.

Indirect lightning effects are less dramatic than from a direct strike, but
they reach further out, either by radiating around the strike, or by
propagating along power lines, telephone system and cable TV. From
the point of view of the home dweller, unwanted opening of the
garage door, or a surge coming from the power company during a
lightning storm, would be seen as indirect effects.

Switching surges occur when electrical loads are turned
on or off (by "Mother's gentle touch" or by some appliance
controls) within your home, as well as by the normal
operations of the power company. An analogy often given
is the "water hammer" that can occur in your piping if a
faucet is turned off too quickly: the electric current flowing in
the wires tries to flow for a short time after the switch has been opened,
producing a surge in the wiring, just like the surge of pressure in the piping,
______________________
You might find useful information about lightning protection on the Web - see page 20.


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¨
How often, how far, how severe ?

So, surges can and do happen !
These questions - how often do surges occur, how far do they travel before
hitting your appliances, how severe are they - must be answered, as well
as possible, so that you can proceed to the next step of taking calculated
risks or making a reasonable investment by purchasing some additional
protection. There are several ways of getting surge protection, from
the simple purchase of a plug-in device from an electronic store (more
on that later) to the installation of protective devices for the whole
house, to be done by an electrician or the power company.

How often ?
You are probably best placed to answer that question if you have lived in your
neighborhood for several years. Lightning is random but can strike more
than one time at the same place. There are now sophisticated means to
record the occurrence of individual lightning strikes; electric utilities and
businesses seek the data to make decisions on the risks and needs for
investing in protection schemes. The reason for mentioning "several
years in your neighborhood" is that the frequency of lightning strikes
varies over the years and the section of the country where you live .

How far, how severe ?
The answers to these two questions are linked: a nearby lightning strike has
more severe consequences than an equal strike occurring farther away.
There is also a wide range in the severity of the strike itself, with the very
severe or very mild being rare, the majority being in mid-range (a current
of about 20,000 amperes for a short time) - but still much shorter than
the blink of an eye.

Calculated risk or insurance ?
The trade off:
A large stack of dollar bills and some
change to replace your unprotected
computer, if and when a lightning or
some other surge destroyed it .....

..... or use a small number of bills to
purchase a "surge protector" for peace
of mind and effective protection.

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