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A/V Power Management -Introduction A/V Power Management -Engineering techniques A/V Power Management - Which devices to buy |
The main job of a surge protector system is to protect electronic devices from "surges." 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 equipment. 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. If the surge (lasts three nanoseconds or more) or spike (lasts one or two nanoseconds) is high enough, it can inflict some heavy damage on a machine. Actually, it heats up components like the filament in a light bulb and many burn them. Even if increased voltage doesn't immediately break your machine, it may put extra strain on the components, wearing them down over time. In the next section, we'll look at what surge protectors do to prevent this from happening. Protection Methods 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. 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 Other Protection Methods As a backup, some surge protectors also have a built-in fuse. A fuse is a resistor that can easily conduct current as long as the current is below a certain level. If the current increases above the acceptable level, the heat caused by the resistance burns the fuse, thereby cutting off the circuit. If the MOV doesn't stop the power surge, the extra current will burn the fuse, saving the connected machine. This fuse only works once, as it is destroyed in the process. Some surge protectors have a line-conditioning system for filtering out "line noise," smaller fluctuations in electrical current. Basic surge protectors with line-conditioning use a fairly simple system. On its way to the power strip outlet, the hot wire passes through a toroidal choke coil. The choke is a just ring of magnetic material, wrapped with wire -- a basic electromagnet. The ups and downs of the passing current in the hot wire charge the electromagnet, causing it to emit electromagnetic forces that smooth out the small increases and decreases in current. This "conditioned" current is more stable, and so easier on your computer (or other electronic device). Transient Sources Power surges occur when something boosts the electrical charge at some point in the power lines. This causes an increase in the electrical potential energy, which can increase the current flowing to your wall outlet. A number of different things can cause this to happen. The most familiar source is probably lightning, though it's actually one of the least common causes. When lightning strikes near a power line, whether it's underground, in a building or running along poles, the electrical energy can boost electrical pressure by millions of volts. This causes an extremely large power surge that will overpower almost any surge protector. In a lightning storm, you should never rely on your surge protector to save your computer. The best protection is to unplug your computer. A more common cause of power surges is the operation of high-power electrical devices, such as elevators, air conditioners and refrigerators. These high-powered pieces of equipment require a lot of energy to switch on and turn off components like compressors and motors. This switching creates sudden, brief demands for power, which upset the steady voltage flow in the electrical system. While these surges are nowhere near the intensity of a lightning surge, they can be severe enough to damage components, immediately or gradually, and they occur regularly in most building's electrical systems. Other sources of power surges include faulty wiring, problems with the utility company's equipment, and downed power lines. The system of transformers and lines that brings electricity from a power generator to the outlets in our homes or offices is extraordinarily complex. There are dozens of possible points of failure, and many potential errors that can cause an uneven power flow. In today's system of electricity distribution, power surges are an unavoidable occurrence. In the next section, we'll see what this could mean to you. Protecting Your Home Theater 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. 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. 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. 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: 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. In the next section, we'll find out what you should look for when considering different models. Picking the Right Surge Protector Shopping for a surge protector is tricky business because there are a lot of nearly worthless products on the market. Research into a particular model is the best way to ensure good results, but you can get a good idea of a product's performance level by looking for a few signs of quality. First of all, look at price. As a general rule, don't expect much from any surge protector that costs less than $10. These units typically use simple, inexpensive MOVs with fairly limited capacities, and won't protect your system from bigger surges or spikes. Of course, high price doesn't promise quality. To find out what the unit is capable of, you need to check out its Underwriters Laboratories (UL) ratings. UL is an independent, not-for-profit company that tests electric and electronic products for safety. If a protector doesn't have have a UL listing, it's probably junk; there's a good chance it doesn't have any protection components at all. If it does use MOVs, they may be of inferior quality. Cheaper MOVs can easily overheat, setting the entire surge protector on fire. This is actually a fairly common occurrence! Many UL-listed products are also of inferior quality, of course, but you're at least guaranteed that they have some surge protection capabilities and meet a marginal safety standard. Be sure that the product is listed as a transient voltage surge suppressor. This means that it meets the criteria for UL 1449, UL's minimum performance standard for surge suppressors. There are a lot of power strips listed by UL that have no surge protection components at all. They are listed only for their performance as extension cords. On a listed surge protector, you should find a couple of ratings. Look for: You should also look for a protector with an indicator light that tells you if the protection components are functioning. All MOVs will burn out after repeated power surges, but the protector will still function as a power strip. Without an indicator light, you have no way of knowing if your protector is still functioning properly. Better surge protectors may come with some sort of guarantee of their performance. If you're shopping for more expensive units, look for a protector that comes with a guarantee on your computer. If the unit fails to protect your computer from a power surge, the company will actually replace your computer. This isn't total insurance, of course -- you'll still lose all the data on your hard drive, which could cost you plenty -- but it is a good indication of the manufacturer's confidence in their product. No surge protector is 100 percent effective, and even top of the line equipment may have some serious problems. Electronics experts are actually somewhat divided over the best way to deal with power surges, and different manufacturers claim other technologies are inherently faulty. If you're interested in learning more about these issues, and finding out all the ways surge protection technology can fail, check out some of the sites listed in the links section on the next page. Surprisingly, surge protectors are an extremely controversial piece of technology, and they have sparked a great deal of debate on the Web.
About Surge Protectors
Another common surge protection device is a gas discharge arrestor, or gas tube. These tubes do the same job as an MOV -- they divert the extra current from the hot line to the ground line. They do this by using an inert gas as the conductor between the two lines. When the voltage is at a certain level, the makeup of the gas is such that it is a poor conductor. When the voltage surges above that level, the electrical power is strong enough to ionize the gas, making it a very effective conductor. It passes on current to the ground line until the voltage reaches normal levels, and then becomes a poor conductor again.
So, if power surges are an inherent part of our electrical system, why didn't we need surge protectors in our homes 50 years ago?
