F

Fiber optic cable - A non-conducting signaling medium which uses a light beam to transmit messages through a cable of thin filaments of glass or plastic. It is therefore unlike other types of cable which use an electric charge on conducting cable to transmit signals.

Filter - Consists of a combination of components that allows only certain frequencies, or a band of frequencies, to pass.

FIPS - Abbreviation for the American Federal Information Processing Standards body

Flash testing - A high voltage test to prove the integrity of electrical insulation

Flashover - A temporary breakdown of insulation, allowing a spark or discharge

Frequency - The number of times per second that an alternating voltage changes polarity from positive to negative. Measure in hertz (Hz). In the United States, the power line frequency is 60 Hz, or 60 cycles per second.

Fuse - Protective device that operates to create an open circuit under overcurrent or fault current conditions

G

G - Abbreviation for giga, meaning 1,000,000,000 or 109. Used as a prefix to units such as frequency (Hz).

Gas discharge tube (GTD) - (also known as gas tube) is a hermetically sealed spark gap. It is an insulator until the voltage between its electrodes exceeds its breakdown voltage, at which point it arcs and crowbars the surge. The gas tube is filled with an inert gas (typically argon) and special low work function coatings, which are applied to the electrodes. As a result, a gas tube can take more surges with a stable predictable breakdown voltage, than an air gap.

Glitch - Voltage increases of no more than millisecond duration. Also referred to as transient overvoltages, spikes, and surges.

Ground - American term for earth, often denoted with a 'G'. For safety reasons, electrical systems in the USA have a wire connected to earth ground at the service entrance. This 'ground' wire is run along with the two current carrying wires.