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This chapter is from the book

Power Devices

Utilizing proper power devices is part of a good preventative maintenance plan and helps to protect a computer. You need to protect against several things:

  • Surges
  • Spikes
  • Sags
  • Brownouts
  • Blackouts

A surge in electrical power means that there is an unexpected increase in the amount of voltage provided. This can be a small increase or a larger increase known as a spike. A spike is a short transient in voltage that can be due to a short circuit, tripped circuit breaker, power outage, or lightning strike.

A sag is an unexpected decrease in the amount of voltage provided. Typically, sags are limited in time and in the decrease in voltage. However, when voltage reduces further, a brownout could ensue. During a brownout the voltage drops to such an extent that it typically causes the lights to dim and causes computers to shut off.

A blackout is when a total loss of power for a prolonged period occurs. Another problem associated with blackouts is the spike that can occur when power is restored. In the New York area, it is common to have an increased amount of tech support calls during July; this is attributed to lightning storms! Quite often this is due to improper protection.

Some devices have specific purposes, and others can protect against more than one of these electrical issues. Let's describe a few of these devices.

Power Strips

A power strip is a group of sockets, usually in-line, with a flexible cable that plugs into an AC outlet. It enables for multiple devices to share a single receptacle in that outlet. Due to this, a maximum wattage rating can be applied to the device, for example, 3,000 watts is a decent amount. Interesting, a computer might have a 300-watt power supply, but on the average, it might use only 100 watts of that power while running. A monitor might use between 35 watts and 100 watts depending on the type of monitor. You can check the wattage rating on the back or side of most devices. Add the total for all devices connected to the power strip, and remember not to exceed the maximum rating. This concept applies to other devices in this section including surge protectors and UPSs.

Power strips might not have surge protection functionality. If they don't have surge protection capabilities, they cannot protect from any of the electrical issues (surges and spikes) listed in the previous section.

A power strip has a master on/off switch and usually has a 15-amp circuit breaker to prevent overloading. If an overload occurs, the circuit breaker trips, cutting power, and the device can usually be reset by pressing a black button normally located somewhere near the power button. Overloads occur because the power strip tries to pull too much current (amps) from the wall outlet, or when too much current is supplied to the power strip. As a rule of thumb, no more than four or five computers (and monitors) should use the same power strip and, therefore, the same circuit. This calls into question whether any other AC outlets connect to the same circuit. To find this out, a qualified electrician can use a circuit testing tool and locate all the outlets on the circuit in question, or this information might be included in your building's electrical diagram. By the way, you can also calculate the amount of computers and monitors that can connect to a circuit by their amperage rating. For example, at AC (wall-outlet level) a typical computer would draw 2 to 3 amps and perhaps another 2 amps for the monitor maximum. (Keep in mind that these are estimates.) So on a standard 15-amp circuit, it would be wise to have no more than three computers and three monitors running simultaneously.

Surge Protectors

A surge protector or surge suppressor is a power strip that also incorporates a metal-oxide varsistor (MOV) to protect against surges and spikes. Most power strips that you find in an office supply store or home improvement store have surge protection capability. The word varsistor is a blend of the two terms variable resistor.

Surge protectors are usually rated in joules, which are a way to measure energy, and in essence, the more joules the better. For computer systems, 1,000 joules or more is recommended. This joule rating gives you a sense of how long the device can protect against surges and spikes. Surges happen more often than you might think, and every time a surge happens, part of the varsistor is burned out. The higher the joule rating, the longer the varsistor (and therefore the device) should last. Most of today's surge protectors have an indicator light that informs you if the varsistor has failed.

Because surges can occur over telephone lines, RG-6 cable lines, and network lines, it is common to see input and output ports for any or all these on a decent surge protector. Higher-quality surge protectors have multiple MOVs not only for the different connections such as AC and phone, but also have multiple MOVs for the individual wires in an AC connection.

Uninterruptible Power Supplies

An uninterruptible power supply (UPS) takes the functionality of a surge suppressor and combines that with a battery backup. So now, our computer is protected not only from surges and spikes, but also from sags, brownouts, and blackouts.

But the battery backup can't last indefinitely! It is considered emergency power and typically keeps your computer system running for 5 to 30 minutes depending on the model you purchase. Figure 5.3 shows an example of a typical inexpensive UPS. Notice that some of the outlets on the device are marked for battery backup and surge protection, whereas others are for surge protection only.

Figure 5.3

Figure 5.3 A common UPS

Most UPS devices also act as line conditioners, protecting from over and under-voltage; they condition (or regulate) the voltage sent to the computer. The device shown, and most UPS devices today, has a USB connection so that your computer can communicate with the UPS. When there is a power outage, the UPS sends a signal to the computer telling it to shut down, suspend, or stand-by before the battery discharges completely. Most UPSs come with software that you can install that enables you to configure the computer with these options.

UPS devices' output power capacity is rated in volt-amps (VA) and watts. Although you might have heard that volt-amps and watts are essentially the same, this is one of those times that they are somewhat different. The volt-amp rating is slightly higher due the difference between apparent power (when in battery backup mode) and real power (when pulling regular power from the AC outlet). For example, the device in Figure 5.3 has a volt-amp rating of 350 VA but a wattage rating of 200 watts. Generally, this is enough for a computer, monitor, and a few other devices, but a second computer might be pushing it given the wattage rating. The more devices that connect to the UPS, the less time the battery can last if a power outage occurs; if too many devices are connected, there may be inconsistencies when the battery needs to take over. Thus many UPS manufacturers limit the amount of battery backup-protected receptacles. Connecting a laser printer to the UPS is not recommended due to the high current draw of the laser printer; and never connect a surge protector or power strip to one of the receptacles in the UPS, to protect the UPS from being overloaded.

The UPS normally has a lead-acid battery that, once discharged, requires 10 hours to 20 hours to recharge. This battery is usually shipped in a disconnected state. Before charging the device for use, you must first make sure that the battery leads connect to the UPS. If the battery ever needs to be replaced, a red light will usually appear accompanied by a beeping sound. Beeping can also occur if power is no longer supplied to the UPS by the AC outlet.

There are varying levels of UPS devices, which incorporate different technologies. For example, the cheaper standby UPS (known as an SPS) might have a slight delay when switching from AC to battery power, possibly causing errors in the computer operating system. Although it isn't important to know these different technologies for the exam, you should realize that some care should be taken when planning the type of UPS to be used. When data is crucial, you had better plan for a quality UPS!

Cram Quiz

Answer these questions. The answers follow the last question. If you cannot answer these questions correctly, consider reading this section again until you can.

  1. Which device should you use to protect against power outages?


    A. Multimeter


    B. UPS


    C. Fedex


    D. Surge protector

  2. You want a cost-effective solution to the common surges that can affect your computer. Which device would be the best solution?


    A. UPS


    B. Surge protector


    C. Power strip


    D. Line conditioner

  3. Which of these is an unexpected increase in voltage?


    A. Sag


    B. Blackout


    C. Spike


    D. Whiteout

Cram Quiz Answers

  1. B. The UPS is the only item listed that protects the computer from power outages like blackouts and brownouts.

  2. B. A surge protector is the right solution at the right price. A UPS is a possible solution but costs more than a surge protector. A line conditioner also would be a viable solution but, again, is overkill. And a power strip doesnt necessarily have surge protection functionality..

  3. C. A spike (or a surge) is an unexpected increase in voltage. A sag is a decrease in voltage, a blackout is a power outage, and a whiteout is a blizzard, which could result in a blackout!.

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