ARCHIVED: What are blackouts, brownouts, spikes, surges, and sags?

Most problems relating to electricity and electronic devices can be traced to conditions of line noise, over-voltage, and under-voltage, which are described as blackouts, brownouts, spikes, surges, and sags. Understanding these conditions can help you make decisions regarding certain safety measures available, and also when to take extra precautions when operating electronics.

Whenever talking about voltage, and electricity in general, it is important to remember that there are two major factors to consider at all times. First, and most obvious, is the strength of the signal. Second, you must also take into account the amount of time such signal strengths are present.

Over-voltage is essentially any voltage greater than what should normally be present on any given power line. Most electronics devices, and especially computers, have internal power supplies that are designed to handle moderate over-voltage conditions (usually a 10% increase) for a very small amount of time without damage. Spikes and surges are both examples of over-voltage conditions. A spike (also referred to as a transient) is a very short over-voltage condition (billionths to millionths of a second), which is rarely harmful to most electronic devices. A surge, on the other hand, can be quite harmful to electronic devices. While surges are sometimes stronger than spikes in terms of volts, usually the damage is done by the length of the surge (thousandths of a second).

Sags, brownouts, and blackouts are all under-voltage conditions. Sags rarely affect electronic devices, while brownouts will usually cause a computer to reboot due to moderate times of under-voltage (lasting up to several seconds). Blackouts, of course, are long periods (minutes to hours) of interrupted service.

While it is impossible to predict when these conditions might occur, there are times when such conditions are more likely to arise. For example, during a rain storm, lightning strikes can cause over-voltage and harm your power line, or can cause under-voltage when electricity-managing devices are struck. It's best not to operate electronic devices at these times, unless they are attached to a quality surge suppressor (which will not prevent your computer from rebooting), or an uninterruptible power supply (UPS).

Also remember that it is possible for power surges on a phone line to damage a computer that is connected through a modem.