Rosewill Computer Case 422 Technical Information PDF herunterladen (Seite 72)

Surge Protectors

155

Disassembly

and Power

When the voltage falls below 110 volts AC, an undervoltage condition exists. If the volt-

age is too low, a computer power supply cannot provide enough power to all the components.

Under these conditions, the power supply draws too much current, causing it to overheat,

weakening or damaging the components. An undervoltage condition is known as a brownout or

sag. Table 4.7 explains these power terms.

Table 4.7 Adverse power conditions

Major type Subtype Explanation

Overvoltage spike A spike lasts 1 to 2 nanoseconds. A nanosecond is one-

billionth of a second. A spike is harder to guard against

than a surge because it has such short duration and high

intensity.

surge A surge lasts longer (3 or more nanoseconds) than a spike.

Also called transient voltage. Causes of surges include

lightning, poorly regulated electricity, faulty wiring, and

devices that turn on periodically, such as elevators, air

conditioners, and refrigerators.

Undervoltage

brownout In a brownout, power circuits become overloaded.

Occasionally, an electric company intentionally causes a

brownout to reduce the power drawn by customers during

peak periods.

sag A sag occurs when the voltage from the wall outlet drops

momentarily.

blackout A blackout is a total loss of power.

Electric companies offer surge protection for homes. Frequently, there are two choices. A

basic package protects large appliances, such as refrigerators, air conditioners, washers, and

dryers. It allows no more than 800 volts to enter the electrical system. A premium package pro-

tects more sensitive devices (TVs, stereos, and computers) and reduces the amount of voltage

allowed to 323 volts or less. Some suppressors handle surges up to 20,000 volts. The exterior

surge arrestor does not protect against voltage increases that originate inside the building,

such as those caused by faulty wiring.

Adverse Power Protection

Power supplies have built-in protection against adverse power conditions. However, the best

protection for a computer is to unplug it during a power outage or thunderstorm. Surge

protectors and UPSs (uninterruptible power supplies) are commonly used to protect against

adverse power conditions. A line conditioner can also be used. Each device has a specific pur-

pose and guards against certain conditions. A technician must be familiar with each device in

order to make recommendations for customers.

Surge Protectors

A surge protector, also known as a surge strip or surge suppressor, is commonly a multi-

outlet strip that offers built-in protection against overvoltage. Surge protectors do not protect

against undervoltage; they protect against voltage increases. Figure 4.31 shows a picture of a

surge protector.

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