A PC's power supply is quite a heroic device when you consider all that it must contend with day in and day out. One thing that can be said for the public electrical supply system is that it is not consistent. Not all of the inconsistency is the electrical company's fault. Many different situations, many beyond the electric company's control, can cause the electricity received at your home or office to fluctuate up or down. The fluctuations on the electrical supply line are what cause the PC (and its power supply) the most trouble.
Six general types of electrical events occur on an electrical power line and reach your PC: line noise, power surges, power spikes, power sags, brownouts, and blackouts. Each of these has its own varying level of impact on the PC power supply, but the PC can be protected from each successfully. It's mostly a matter of how much you want to spend to protect your system.
Line Noise
Every electrical circuit has a certain amount of electrical line noise, which is electromagnetic interference (EMI) caused by many sources, both from nature and electrical equipment. Most EMI comes from electrical equipment, such as a motor, welder, fluorescent lighting, and radio transmitters. An electrical supply line that is shared with noisy electrical equipment very often carries the electrical noise of the equipment over the circuit to other devices connected to the circuit. An example is what happens to your AM radio or
the TV set when a vacuum cleaner is operated on the same electrical circuit. The static you hear is electrical noise. Nearby electrical storm can also be picked up by the electric supply and transmits EMI over the supply lines.
Nearly all PC power supplies are built to handle normal levels of line noise, but excessive line noise often passes through the power supply to the motherboard, disk drives, and any other devices connected to the power supply. Line noise can cause serious problems for a PC or a server if it is not protected. The types of problems that can develop from electrical line noise include memory errors, data loss, circuit connection loss, data transmission problems, and frequent system lockups.
Power Surges
The nominal operating voltage of the AC (alternating current) electricity supplied to the
wall outlets in your house or office is 110 volts, and that's what the power company will tell you is the voltage of your wall outlets. However, in real life, the actual voltage on the line can vary between 85 and 135 volts, and most PC power supplies have a strong enough operating range to handle power fluctuations within a certain range. Most ATX form factor power supplies (see Chapter 14 for more information on the PC power supply) have operating ranges like 92 to 130 volts AC or 90 to 135 volts. Systems designed to operate on 220 volts AC or that can be switched between 110 volt service and 220 volt service typically have an operating range of 180 to 270 volts AC.
Certain disturbances in the area, such as a lightning storm, distant lightning strikes, or problems on the electrical power supply grid such as a major factory shutting down all at once or a sudden drop in the load on the supply lines can cause the voltage on the line to suddenly increase. This sharp increase of voltage is an over voltage event called a surge. An electrical surge is a temporary increase of voltage on the line. A surge is like a rogue wave of electricity that can increase the voltage to as much as 1,000 volts. It typically does this for only a few thousandths of a second, but that's plenty of time to damage anything in its path. Power surges are very common when the power returns from a blackout (see "Blackouts" a little later in this section).
PC power supplies are designed to withstand voltage surges to certain levels, and most are subjected to a few a year. However, even the best power supply will begin to lose its ability to withstand a power surge and can in time begin to fail or begin passing the surge on to internal PC devices connected to it. It is also common for power surges to happen in clusters, which can be fatal for an unprotected system.
Power Spikes
A power spike is a sudden, usually one time, extremely high voltage peak of over voltage on the electrical line. A typical cause of a power spike is lightning striking within a few miles of your vicinity. Lightning carries millions of volts, and if your home or office takes a direct hit, your PC is very likely to be heavily damaged, right along with everything else electrical in the building. Lightning directly striking a building is a fairly rare event, but even a strike within several miles can create an electrical current in metal objects near the
strike. This means that any wires or cables in the area can pick up an electrical spike and pass it to whatever is connected to it. The wire or cable could be a power cable on a PC, a telephone wire, the electricity supply to a house or building, and so on. The chances are slim that your home or office will be directly struck by lightning any time soon, but the odds of a lightning strike near you are pretty good.
Power Sags or Dips
Sudden demands for power on the power grid can create a wave of low voltage on the electrical supply system, which is called a sag or a dip. As the name suggests, a power sag is the opposite of a power surge it's a temporary dip in the voltage on the supply line that usually lasts only a fraction of a second. Power sags that extend below the normal operating voltage range of a system are rare, but they can happen.
Most of the components in the PC are not designed to operate at very low voltages, even for a very short time. The PC's power supply has some power in reserve to pull up short power sags. However, a series of power sags in a short time can affect the power supply's ability to provide the correct voltages to internal PC components and could weaken, damage, or destroy them.
Brownouts
When the demand for electrical power exceeds the capability of the electrical supply system, the result is reduced voltage for everyone, or what is called a brownout. Brownout is meant to indicate that while there is enough power on the grid to prevent a blackout, or a total loss of power, there isn't enough power to meet the current demand. Brownouts frequently occur during extreme weather conditions, such as a sudden abnormally cold or hot spell, when everyone is running their heat or air conditioning.
A brownout is when the voltage on the electrical supply circuit is less than 105 volts AC for an extended time, which could be minutes or hours. A brownout strains the PC in the same way as a power sag, but because a brownout lasts longer, the result can be immediate failure of some components, a burned out power supply, or in an extreme case, the corruption or loss of data. Brownouts are a tool employed by the power companies to shift supply around the grid to meet the demands in specific areas on a rolling basis, or what is called rolling brownouts, and the damage to a PC is often not noticed right away. However, the strain on a PC's components accumulates and eventually results in a failure that is nearly impossible to troubleshoot. Brownouts are far harder on computer equipment than blackouts.
Blackouts
A blackout is a complete loss of a PC's electrical source. Typically, you think of a blackout as a failure of the power supply grid over an entire area, but a blackout can occur in just a part of a building, an entire building, a block, a section of a city, or an even larger area. A blackout event is a sudden complete drop off of the power source, which can
cause a wide range of problems on a PC or a network. At minimum, all of the data in RAM is usually lost, but depending on the applications or utilities running on the PC, much worse could happen. For example, if you are in the middle of flashing the BIOS on a PC when the power fails, the PC must be recovered through the boot block and the BIOS flashing operations repeated. In the interim, the PC is not usable. Or, if the PC is performing a defrag operation, updating the file system tables, or any other system maintenance activity, the PC may be compromised.
Blackouts are caused by electrical storms; car accidents involving utility poles; the electrical utility company being unable to meet user demands, such as the recent problems in California when they used rolling blackouts to try to satisfy user demands; or a total collapse of the power system due to user overload.
Typically, a blackout doesn't just happen, and a series of surges and spikes occurs both before the crash and when the power is restored. The damage to a PC happens not from the power failing but from the power surge on the power supply system when the power is restored.
