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Surge Protection 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. 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 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 my 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.

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.

Image of a normal line voltage 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...
Image of a sag 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.
Image of a swell 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.
Image of noise 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.

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.

Understanding Typical Specifications

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".

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.  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 for. Some packages also provide a cut-off and reset feature in cases of large swells, protecting the protector itself as well as the load.

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.

If I install one plug-in surge protector in one room, are the receptacles in other rooms also protected?

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.

Will a surge protector installed at the service entrance be sufficient for the whole house?

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, before they enter the house. A service-entrance surge protector makes the protection by plug-in protectors easier but, installation at the service entrance generally requires an electrician, unless you are a do-it-yourself person and your city code allows it.

Do surge protectors degrade over time?

Many, if not all, electronic components will age and have a limited life. The question is really how long a useful life can a surge protector have. Today's well- designed surge protectors might reach their end of life prematurely if exposed to some exceptionally high and rare stress but, for those tested according to UL 1449 Second Edition, the way they fail should not be a hazard. The prevailing opinion among specialists on surge protection is that most of the observed (and quite rare) catastrophic failures of surge protectors are caused by excessively high line voltage that can occur when there is a fault on the power system. Failure from very large surges that might exceed the surge-handling capability of the protector is less likely than failure from high line voltage.

And now, the "bottom line" question:

How much money should I spend on surge protection?

It depends on too many factors to give a simple answer. Technology can change, additional features beyond basic surge protection vary, stores offer "specials", and how much margin makes you feel comfortable is an intangible factor. This booklet is not oriented toward rating product performance or prices, but rather toward explaining the principles, so that you can make an informed decision that will give you confidence.

For further information contact the FCIC.

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