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CompTIA A+ Certification All-in-One Exam Guide

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amperage output is too low, the device won’t run. If the polarity is reversed,

it won’t work, just like putting a battery in a flashlight backward. If either the

voltage or amperage—especially the former—is too high, on the other hand,

you can very quickly toast your device. Don’t do it! Always check the

voltage, amperage, and polarity of a replacement AC adapter before you plug

it into a device.

1002

Equipment Grounding

Computer equipment safety starts with proper grounding. The ground wire

functions as an emergency outlet for excess current in case of any short or

malfunction of a device. Don’t assume that a convenient three-prong outlet

has proper grounding, especially in older buildings. Use a multimeter to

check that ground wire.

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 in such scenarios, 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.

EXAM TIP Large sags in electricity are also known as brownouts. When

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