The power you get from the wall outlet is known as "120 volts AC power."
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. This 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.
Normal - 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...
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.
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.
Noise is a catch word sometimes used to describe very small and
persistent disturbances. These do not have damaging effects but can be a
There is, of course, the ultimate disturbance: an outage -no voltage at
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 sensitive appliances in
Your home contains all sorts, types or kinds of appliances. These not
only include 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).
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.
Where do surges come from?
There are two origins for the surges that occur in your power system:
lightning surges and switching surges.
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
We will look at ways of protecting your 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 lightning rods. 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 this
information will help ensure your home has a well- protected electrical
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
Switching surges occur when electrical loads are turned on or off 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.
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, to the
installation of protective devices for the whole house, to be done by an
electrician or the power company.
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.
If you look at it from that point of view, the choice is probably easy
and, most likely, you will be looking for one of those "surge protectors"
-or some device with a similar name to do the same job, as explained next.
What's in a name?
When you walk in the computer store or electronic supply store, you might
ask for something to protect your appliances against surges, but what to
call it ? The devices that can protect against surges are called
"surge-protective devices" by engineers, but that sounds too much like
jargon to some people.
One name that seems to stick is "surge suppressor" with a variety of
trademark names. The Underwriter's Laboratories chose to call them
"Transient Voltage Surge Suppressor" and you might find that name or the
TVSS acronym next to the listing on the product. Always make sure that the
product has been tested by a product safety testing organization, such as
UL, ETL, or CSA, as indicated by their labels.
You cannot really suppress a surge altogether, nor "arrest" it (although
your utility uses devices they call "surge arresters" to protect their
systems). What these protective devices do is neither suppress nor arrest a
surge, but simply divert it to ground, where it can do no harm.
Surge protectors come in many shapes and forms for many purposes, not
just the plug-in kind that you find in the electronic stores. There are
several ways to install them on your power supply: plug and play,
do-it-yourself, hire a licensed electrician to do it, or even call on your
power company to do it. Here is a run down on your options, and who does it:
- Purchase one or more plug-in surge protectors
- Install a surge protector at the service entrance panel
- Have the power company install a surge protector next to the meter
Plug-in surge protectors
This is the easiest solution, and there are a wide variety of brands
available in the stores. These come in two forms: a box that plugs directly
into a wall receptacle, or a strip with a power cord and multiple outlets.
Depending on the appliance, you will look for a simple AC power plug-in, or
a more complex combined protector for AC power and telephone or cable.
However, before you purchase the right protector for the job, you should
think about some details.
There is another decision to make, concerning how a surge protector will
power your appliance if the protective element should fail under extreme
cases of exposure to a large surge or large swell. Most surge protectors are
provided internally with some kind of fuse that will disconnect in case of
failure. However, this disconnect can operate in two different ways,
depending on the design of the surge protector: some will completely cut off
the output power, others will disconnect the failed element but maintain the
Quit and be protected or continue?
For you, it is a matter of choice: would you want to maintain the output
power to your appliance -but with no more surge protection? Or would you
rather maintain protection for sure -by having the circuit of the protector
cut off the power supply to your appliance, if the protective function were
to fail? To make an intelligent decision, you must know which of the two
possibilities are designed into the surge protector that you will be looking
What are the lights telling you?
To help the consumer know what is going on inside the surge protector,
many manufacturers provide some form of indication, generally by one or more
pilot lights on the device. Unfortunately, these indications are not
standardized, and the meaning might be confusing, between one, two - even
three or four lights -where it is not always clear what their color means.
Read the instructions!
More decisions ...
So far, we have looked mostly at the plug-in surge protectors because
they are the easiest to install and they do not require the services of an
electrician. The two other possible locations for surge protectors are the
service panel (breaker panel) and the meter socket.
Service-panel surge protectors
Instead of using several plug in protectors -one for each sensitive
appliance is sometimes recommended -you can install a protector at the
service panel of the house (also called "service entrance" or "breaker
box"). The idea is that with one device, all appliances in the house can be
protected, perhaps with a few plug-in protectors next to the most sensitive
appliances. There are two types of devices available: incorporated in the
panel, or outside the panel.
Some breaker panel manufacturers also offer a snap in surge protector,
taking the space of two breakers (assuming that there are blank spaces
available on the panel), and easily installed by the home owner or by an
electrician. However, there are two limitations or conditions to that
The snap in protectors generally fit only in a breaker panel from the
same manufacturer -possibly down to the model or vintage of the panel.
To install the snap in protector, you must remove the front panel (do
turn off the main breaker before you do that). Most cities have codes
allowing the home owner to do it, under some conditions. Check with your
local authorities to find out if they allow you to do that, or hire a
licensed electrician to do the installation for you. There are other surge
protectors packaged for wiring into the service panel, either within or next
to the panel. That kind of installation is best left to a licensed
At the meter socket
There might be a possibility that the power company in your area offers,
as an option, to install a surge protector with a special adapter, fitting
it between the meter and its socket (the dark band in the bubble of the
picture). But that type of device and installation is out of the question as
a do-it-yourself project, and will require cooperation from the power
company, if they do offer the program.
Other types of outdoor surge protectors can be installed near the meter.
That kind of installation must be done by a licensed electrician.
Before you decide which way you want to protect your appliances, there
are other points to consider.
Where do you live?
This is an important question because the type of dwelling has some
effect on how severe your surge problem might be. In a somewhat simplified
way, consider three categories according to the arrangement of the
- Detached house with power and telephone and/or cable TV drops at
opposite ends of the house -the worst possible arrangement of all. But do
not fret, there is a way of compensating, even after the fact, for this
unfortunate situation, as we will see.
- Detached house with all services (power, cable TV, phone) entering on
the same side of the house.
- Townhouse or apartment building with services entering the building at
one point and fanned out to the different dwellings - about the same as
the case of the detached house with all services on the same side.
What appliances are you using?
From the surge protection point of view, there are four kinds of
appliances, with examples listed below by order of increasing sensitivity to
surges, either because of their nature or because of their exposure:
- Motor-driven and heating appliances
Washers (dish and clothes), food processors, power tools, heating and
ventilation motors, pumps, etc.
Water heaters, space heaters, toasters, incandescent light bulbs
- Free-standing electronic appliances
Computers without modem, table radios, TV sets with rabbit ears Compact
fluorescent and modern tube type fluorescent lamps
- Communications-connected appliances
Computers with modem, TV with cable or satellite antenna, fax machines,
telephone answering/recording machines
- Signal systems
Intruder alarms, garage door openers, sprinklers, intercom
Let's then take a quick look at each of these and see which might need
some form of surge protection.
Motor-driven appliances and heating appliances
For each of these two categories, there can be two or more kinds,
depending on the type of control used.
- Mechanical control (ON-OFF switch, rotary control, etc.), no
sophisticated key pad or other electronic control
- Electronic control (programmable operation, key pad, display, etc.)
Appliances with mechanical controls are generally insensitive to surges
and can be expected to withstand the typical surges that occur in a
residence. Extreme cases, such as a direct lightning strike to the building,
or one to the utility, very close, might cause damage.
Appliances with electronic controls can be more susceptible to damage
than those with mechanical controls. Less traumatic but annoying can be
upset memory in programmable appliances, although progress is being made in
providing more built in protection.
Another difference to be noted is that of appliances permanently
connected, as opposed to those in intermittent use. The risk of a damaging
surge happening at the time of intermittent use is much smaller than that of
an appliance which is on all the time.
What kind of appliances?
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.
This information should help you make the choices that fit your needs for
surge protection. 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
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 Clamp, 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.
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. Fortunately, you can find a special type of surge
protector against the problem, as described next.
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. 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 data.
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 strikes.
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 specific 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.
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.
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:
protection the pump motor itself against surges, and protection 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 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.