CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [143]
Figure 10-7 Circuit tester
Protecting the PC from Spikes and Sags in AC Power
If all power companies could supply electricity in smooth, continuous flows with no dips or spikes in pressure, the next two sections of this chapter would be irrelevant. Unfortunately, no matter how clean the AC supply appears to a multimeter, the truth is that voltage from the power company tends to drop well below (sag) and shoot far above (surge or spike) the standard 115 V (in the United States). These sags and spikes usually don’t affect lamps and refrigerators, but they can keep your PC from running or can even destroy a PC or peripheral device. Two essential devices handle spikes and sags in the supply of AC: surge suppressors and uninterruptible power supplies.
Surge Suppressors Surges or spikes are far more dangerous than sags. Even a strong sag only shuts off or reboots your PC; any surge can harm your computer, and a strong surge destroys components. Given the seriousness of surges, every PC should use a surge suppressor device that absorbs the extra voltage from a surge to protect the PC. The power supply does a good job of surge suppression and can handle many of the smaller surges that take place fairly often. But the power supply takes a lot of damage from this and will eventually fail. To protect your power supply, a dedicated surge suppressor works between the power supply and the outlet to protect the system from power surges (see Figure 10-8).
Figure 10-8 Surge suppressor
Most people tend to spend a lot of money on their PC and for some reason suddenly get cheap on the surge suppressor. Don’t do that! Make sure your surge suppressor has the Underwriters Laboratories UL 1449 for 330 V rating to ensure substantial protection for your system. Underwriters Laboratories (www.ul.com) is a U.S.-based, not-for-profit, widely recognized industry testing laboratory whose testing standards are very important to the consumer electronics industry. Additionally, check the joules rating before buying a new surge suppressor. A joule is a unit of electrical energy. How much energy a surge suppressor can handle before it fails is described in joules. Most authorities agree that your surge suppressor should rate at a minimum of 800 joules—and the more joules, the better the protection. My surge suppressor rates out at 1,750 joules.
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CAUTION No surge suppressor in the world can handle the ultimate surge, the ESD of a lightning strike. If your electrical system takes such a hit, you can kiss your PC goodbye if it was plugged in at the time. Always unplug electronics during electrical storms!
While you’re protecting your system, don’t forget that surges also come from telephone and cable connections. If you use a modem, DSL, or cable modem, make sure to get a surge suppressor that includes support for these types of connections. Many manufacturers make surge suppressors with telephone line protection (see Figure 10-9).
Figure 10-9 Surge suppressor with telephone line protection
No surge suppressor works forever. Make sure your surge suppressor has a test/reset button so you’ll know when the device has—as we say in the business—turned into an extension cord. If your system takes a hit and you have a surge suppressor, call the company! Many companies provide cash guarantees against system failure due to surges, but only if you follow their guidelines.
If you want really great surge suppression, you need to move up to power conditioning. Your power lines take in all kinds of strange signals that have no business being in there, such as electromagnetic interference (EMI) and radio frequency interference (RFI). Most of the time, this line noise is so minimal it’s not worth addressing, but occasionally events (such as lightning) generate enough line noise to cause weird things to happen to