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   Power problems


■    ESD problems


■    EMI problems


■    RFI problems


■    Climate problems

Power Problems


Alternating current (AC), which is “food” to PCs and other network devices, is normally 110 volts and changes polarity 60 times a second (or 60 Hertz). These values are referred to as line voltage. Any deviation from these values can create problems for a PC or other network device. Power problems fall into three categories:


■    Overage


■    Underage


   Quality

Power Overage Problems


During a power overage, too much power is coming into the computer. Power overage can take two forms:


■    A power spike occurs when the power level rises above normal levels and then drops back to normal in less than one second.


■    A power surge occurs when the power level rises above normal levels and stays there for more than one or two seconds.


Typically, power surges last longer than a second or two, and they may last for several minutes. For this reason, surges are usually more damaging than spikes (although a very large spike can damage a computer’s power supply just as much as a surge). Figure 6.1 shows the difference between a spike and a surge.


6.1 Comparing a power spike and a power surge


Voltage


Two types of devices are used to protect computers and other network devices from power overage problems:


■    Surge protectors


■    Line conditioners


A surge protector contains a special electronic circuit that monitors the incoming voltage level and trips a circuit breaker when the overvoltage reaches a certain level (called the overvoltage threshold). The problem with surge protectors is that the threshold is set too high to be safe. By the time the circuit breaker trips, some overvoltage has gotten to the power supply of the computer, possibly damaging it. Nor does a surge protector protect against power surges and spikes that are lower than the threshold. For the most part, a surge protector is better than nothing, but not by much. It is really only a multiple-outlet strip and should not be considered anything more.

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