Sags: These are defined as a decrease in voltage, may last for a few cycles or for many seconds. A brownout is also another name for a sag of very long duration. The cause of sags is usually some high loading of the power system, which causes the voltage to drop. Sags can be caused by the heaters on large copy machines cycling on and off.
Spikes: Spikes can be either internally or externally generated and are often caused by the power system recovering from a deep short sag. If an overload is suddenly removed, the voltage will rebound to a very high value for a short period of time. The resultant spike can be several times the normal line voltage.
Swells: Swells usually result from the load on a utility distribution system being reduced more quickly than voltage regulators can respond. Swells are usually not associated with specific equipment failure, but can result in shortened lifetime for motors and particularly incandescent lighting.
Outages: An outage is a complete loss of power. Outages are usually due to some major event on the utility distribution system, and can last from only a few cycles up to days. Outages are often caused by lightning, car accidents or may be weather related.
Power surges: These are transient over-voltages that are conducted on wires and cause damage to computers, modems and other electronic equipment. These also come about as a result of lightening and switching reactive loads
Because of these conditions, modern electrical devices should be designed with sufficient power handling components and capabilities to prevent damage that can be caused by the power quality problems mentioned above. Despite being totally different effects and conditions, all of them can cause failure of electrical devices at any given time. Therefore, to correct this problem, all equipment should be tested during the prototyping stage under a controlled environment where the exact power conditions being tested can be effectively simulated. This will aid designers of consumer electronics in ascertaining that their newest appliances will be able to stand up to fluctuations in power conditions at their input. Additionally, such equipment could be utilized by governmental or independent study groups in external testing of existing consumer appliances to make sure that the devices adhere to sufficient safety and reliability standards for the public good.
Once the equipment has been tested, the threshold of voltages that can hurt different electronic appliances such as computers can be established, and then precautionary devices and measures are added for protection. This helps in assuring the owner of an electronic device such as a computer that his or her data and files will be safe even if there is a thunderstorm, and he or she can maintain communication lines during such conditions. Also the equipment owner will worry less about safety of personal property from concerns such as fire and electrical shock.