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Power Surges and What They Are

Surge Basics:
The main job of a surge protector system is to protect electronic devices from "surges." So if you're wondering what a surge protector does, the first question is, "What are surges?" And then, "Why do electronics need to be protected from them?"

A power surge, or transient voltage, is an increase in voltage significantly above the designated level in a flow of electricity. In normal household and office wiring in the United States, the standard voltage is 120 volts. If the voltage rises above 120 volts, there is a problem, and a surge protector helps to prevent that problem from destroying your computer.

To understand the problem, it is helpful to understand something about voltage. Voltage is a measure of a difference in electric potential energy. Electric current travels from point to point because there is a greater electric potential energy on one end of the wire than there is on the other end. This is the same sort of principle that makes water under pressure flow out of a hose -- higher pressure on one end of the hose pushes water toward an area of lower pressure. You can think of voltage as a measure of electrical pressure.

As we'll see later on, various factors can cause a brief increase in voltage:

  • When the increase lasts three nanoseconds (billionths of a second) or more, it's called a surge.
  • When it only lasts for one or two nanoseconds, it's called a spike.

If the surge or spike is high enough, it can inflict some heavy damage on a machine. The effect is very similar to applying too much water pressure to a hose. If there is too much water pressure, a hose will burst. Approximately the same thing happens when too much electrical pressure runs through a wire -- the wire "bursts." Actually, it heats up like the filament in a light bulb and burns, but it's the same idea. Even if increased voltage doesn't immediately break your machine, it may put extra strain on the components, wearing them down over time.

The Process of Protection:
A standard surge protector passes the electrical current along from the outlet to a number of electrical and electronic devices plugged into the power strip. If the voltage from the outlet surges or spikes -- rises above the accepted level -- the surge protector diverts the extra electricity into the outlet's grounding wire.

In the most common type of surge protector, a component called a metal oxide varistor, or MOV, diverts the extra voltage. As you can see in the diagram below, an MOV forms a connection between the hot power line and the grounding line.

An MOV has three parts: a piece of metal oxide material in the middle, joined to the power and grounding line by two semiconductors.

These semiconductors have a variable resistance that is dependent on voltage. When voltage is below a certain level, the electrons in the semiconductors flow in such a way as to create a very high resistance. When the voltage exceeds that level, the electrons behave differently, creating a much lower resistance. When the voltage is correct, an MOV does nothing. When voltage is too high, an MOV can conduct a lot of current to eliminate the extra voltage.

As soon as the extra current is diverted into the MOV and to ground, the voltage in the hot line returns to a normal level, so the MOV's resistance shoots up again. In this way, the MOV only diverts the surge current, while allowing the standard current to continue powering whatever machines are connected to the surge protector. Metaphorically speaking, the MOV acts as a pressure-sensitive valve that only opens when there is too much pressure.

They are inexpensive, and can help prevent costly repairs.

Basic Surge Protector

Protecting Your Equipment: In the last section, we saw that power surges are a regular occurrence, unavoidable with our current system of providing electricity to homes and offices. This raises an interesting question: If power surges are an inherent part of our electrical system, why didn't we need surge protectors in our homes 50 years ago?

The answer is that a lot of the components in sophisticated modern electronic devices (such as computers, microwaves, DVD players) are much smaller and more delicate than components in older machines, and are therefore more sensitive to current increases. Microprocessors, which are an integral part of all computers as well as many home appliances, are particularly sensitive to surges. They only function properly when they receive stable current at the right voltage.

So whether or not you should get a surge protector depends on what sort of device you're hooking up to the power supply.

  • There's no reason to hook up a light bulb to a surge protector because the worst that is likely to happen due to a power surge is that your light bulb will burn out.
  • You should definitely use a surge protector with your computer. It is filled with voltage-sensitive components that a power surge could damage very easily. At the least, this damage will shorten the life of your computer, and it could very easily wipe out all of your saved data or destroy your system. Computers are very expensive items, and the data they hold is often irreplaceable, so it's only good economic sense to invest in a quality surge protector.
  • It's a good idea to use surge protectors for other high-end electronic equipment, such as entertainment center components. A surge protector will generally extend the life of these devices, and there's always a chance that a big power surge will causes severe damage.
One problem with surge protectors is that the MOVs can burn out with one good surge. This is why it's good to get a protector with an indicator light that tells you whether or not it's functioning properly.

Even if you connect surge protectors to all of your outlets, your equipment might be exposed to damaging surges from other sources. Telephone and cable lines can also conduct high voltage -- for full protection, you should also guard against surges from your telephone or cable lines. Any lines carrying signals into your home can also carry a power surge, due to lightning or a number of other factors. If your computer is connected to the phone lines via a modem, you should get a surge protector that has a phone-line input jack. If you have a coaxial cable line hooked up to expensive equipment, consider a cable surge protector. Surges on these lines can do just as much damage as surges over power lines.

Levels of Surge Protection: All surge protectors are not created equal. In fact, there is a tremendous range in both performance and price of protection systems.
  • At one end, you have your basic $5 surge protector power strip, which will offer very little protection.
  • On the other end you have systems costing hundreds of thousands of dollars, which will protect against pretty much everything short of lightning striking nearby.
This inexpensive, quality protector features basic MOV protection and line-conditioning systems.

Most systems have limitations of some sort; picking out a protector system that suits you is a matter of balancing the cost of the system with the cost of losing data or electronic equipment. As with insurance, you find the level of coverage you're comfortable with.

Surge Arrestors:
You can also install a "whole-house" surge arrestor. You generally install these units near your electric meter, where the power lines run to your building. This protects all the circuits in your house or office from a certain range of voltage surges. Units designed for whole-house protection are generally built for outdoor installation. Better surge arrestors can handle surges up to 20,000 volts, while standard outlet surge protectors can't handle more than 6,000 volts. Some high-end arrestors can actually monitor weather conditions and will shut down the power supply to more sensitive electronics when lightning is in the area. A whole-house surge protector will suppress power surges stemming from outside sources -- utility company problems, transformer switching, etc. -- but won't do anything to suppress the high number of power surges that originate inside your house, due to the operations of your appliances.

To protect your equipment from surges, you need individual surge protectors for each outlet. These power strips range a great deal in quality and capacity (as we'll see in the next section). There are three basic levels of power strip surge protectors:

  • Basic power strip - These are basic extension cord units with five or six outlets. Generally, these models provide only basic protection.
  • Better power strip - For $15 to $25 you can get a power strip surge protector with better ratings and extra features, such as a protection indicator light and individual switches for each outlet.
  • Surge station - These large surge protectors fit under your computer or on the floor. They offer superior voltage protection and advanced line conditioning. Most models also have an input for a phone line, to protect your modem from power surges, and may feature built-in circuit breakers. You can get one of these units for as little $30, or you can spend upward of $100 for a more advanced model.
  • Uninterruptable Power Supply (UPS) - Some units combine surge protection with a continuous UPS. The basic design of a continuous UPS is to convert AC power to DC power and store it on a battery. The UPS then converts the battery's DC power back to AC power and runs it to the AC outlets for your electronics. If the power goes out, your computer will continue to run, feeding off the stored battery power. This will give you a few minutes to save your work and shut down your computer. The conversion process also gets rid of most of the line noise coming from the AC outlet. These units tend to cost $150 or more.

An ordinary UPS WILL give you a high level of protection, but you should still use a surge protector. A UPS will stop most surges from reaching your computer, but it will probably suffer severe damage itself. It's a good idea to use a basic surge protector, if just to save your UPS.

Once you've decided what level of surge protection you need, it's time to shop around for a good unit.


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