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- Failure, degradation
Failure that is both gradual and partial. Note: In time, such failure may develop into complete failure. - Flicker
A variation of input voltage sufficient in duration to allow visual observation of a change in electric light source intensity. - Form factor (periodic function)
The ratio of the root mean square value to the average absolute value, averaged over a full period of the function. - Forward transfer impedance
An attribute similar to internal impedance, but at frequencies other than the nominal (for example, 60 Hz power frequency) – knowledge of the forward transfer impedance allows the designer to assess the capability of the power source to provide load current (at the harmonic frequencies) needed to preserve a good output voltage waveform – generally, the frequency range of interest is 60 Hz – 3 kHz, for 5 – 60 Hz power systems and 20–25 kHz for 380–480 Hz power systems. - Ground (Earthing)
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.
Note: It is used for establishing and maintaining the potential of the earth (or of the conducting body) or approximately that potential, on conductors connected to it, and for conducting ground currents to and from each (or the conducting body). - Ground electrode
A conductor or group of conductors in intimate contact with the earth for the purpose of providing a connection with the ground. - Ground electrode, concrete encased
A grounding electrode completely encased within concrete, located within and near the bottom of a concrete foundation or footing or pad, that is in direct contact with the earth. - Ground grid
A system of interconnected base conductors arranged in a pattern over a specified area and buried below the surface of the earth – the primary purpose of the ground grid is to provide safety for workmen by limiting potential differences within its perimeter to safe levels in case of high currents, which could flow if the circuit being worked became energized for any reason or if an adjacent energized circuit faulted – metallic surface mats and gratings are sometimes utilized for the same purpose – this term should not be used when referring to a signal reference structure. - Ground impedance tester
A multi-functional instrument designed to detect certain types of wiring and grounding problems in low-voltage power distribution systems. - Ground loops
A potentially detrimental loop formed when two or more points in an electrical system that are nominally at ground potential area connected by a conducting path such that either or both points are not at the same ground potential. - Harmonic distortion
The mathematical representation of the distortion of the pure sine waveform. - Isolated equipment ground
An insulated equipment grounding conductor run in the same conduit or raceway as the supply conductors – this conductor is insulated from the metallic raceway and all ground points throughout its length. It originates at an isolated ground type receptacle or equipment input terminal block and terminates at the point where neutral and ground are bonded at the power source (this term is defined more specifically in the NEC [2], Sections 250–74 and 250–75).