# Common Power Quality Terms

AFI (also AFCI): Arc fault interrupter, or arc fault circuit interrupter: designed to help prevent fires by detecting an unintended electrical arc and disconnecting the power before the arc starts a fire. An AFCI must distinguish between a harmless arc that occurs incidental to normal operation of switches, plugs and brushed motors and an undesirable arc that can occur.

Blackout: A cutoff of electrical power, especially as a result of a shortage, a mechanical failure, or overuse by consumers

Brownout: Common term for under voltage, taken from the coloration of filament style light bulbs during under voltage conditions

Flicker: A small change in line voltage, which causes a perceptible change in the intensity of electric lights. In some situations people can detect sags as low as a third of a volt

GFI (also GFCI): ground fault interrupter, or ground fault circuit interrupter, an electrical device that senses a fault in the electrical system and shuts down power to that device

Ground: A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth or to some conducting body of relatively large extent that serves in place of the earth

Harmonic: A harmonic is a signal or wave whose frequency is an integral (whole-number) multiple of the frequency of the main power frequency (ours is 60Hz). These can cause many problems and should be remedied as soon as detected.

Joule Ratings: This is the amount of energy a unit can dissipate before it fails -- the higher the rating the better.

Load: how much electricity or energy you use in a given period of time

Open Circuit: a circuit having a break in it so that current is not passing or cannot pass (generally a blown fuse)

Over-voltage: When used to describe a specific type of long-duration variation, refers to a voltage having a value of at least 10 percent above the nominal voltage for a period of time greater than 1 min.

Short Circuit: A low-resistance connection established by accident or intention between two points in an electric circuit

Transient: A sudden, brief increase in {current} or {voltage} in a circuit that can damage sensitive components and instruments

UL Rating: UL (Underwriters Laboratory) is a non-profit organization that test electronic products for their safety

Under-voltage: When used to describe a specific type of long-duration variation, refers to a measured voltage having a value at least 10 percent below the nominal voltage for a period of time greater than 1 min. In other contexts, such as distributed generation protection, the time frame of interest would be measured in cycles or seconds.

Voltage Sag: A decrease of 10 to 90% in the RMS voltage at the power frequency for durations of one-half cycle to 1 minute

Voltage Swell: A temporary increase in the RMS value of voltage of more than 10% at the power frequency, for durations from one-half cycle to one minute (commonly called a surge)