H

Harmonics - A continuous distortion of the normal sine wave, at frequencies of up to 3kHz.

Harmonic Distortion - The misshapen or distorted sinusoidal waveform resulting from the algebraic addition (to the fundamental wave shape) of higher frequency sine waves, which are multiples of the fundamental frequency. These multiples of the fundamental frequencies are denoted as harmonics. Algebraically adding the fundamental and the 3rd harmonic results in a harmonically distorted wave shape.

Headroom - The voltage difference between the peak of the 50/60 Hz power line sine wave voltage and the "Threshold Voltage" of the suppression device. A minimum spacing of 15%above the sine wave peak is considered essential.

Hertz (Hz) - Unit of frequency representing one cycle per second of alternating current.

High voltage (HV) - Voltage exceeding 1,000 volts AC or 1,500 volts DC between conductors (L-L or L-N), or 600 volts AC or 900 volts DC between conductors and earth (L-G, N-G).

HV - Abbreviation for high voltage

Hybrid generator - Alternative name for combination wave generator

Hz - Abbreviation for Hertz

I

IEC - Abbreviation for International Electrotechnical Committee

IEEE - Abbreviation for The (American) Institutes of Electrical and Electronics Engineers. Many IEEE publications have been adopted as American National Standards

IEEE 587-1980 - A technical standard originally published in 1981 by the Institute of Electrical and Electronic Engineers (IEEE). It was superseded by IEEE C62.41 -1991 and is recognized as an American National Standard.

Impedance - A measure of the response of an electric circuit to an alternating current. In addition to the resistance, the current is also opposed by the capacitance and inductance of the circuit. Impedance is this combined oppositions to current flow.

In-line or series - Component of device installed within a voltage is generated by a change in the current, either in the circuit itself (self-inductance) or in a neighboring circuit (mutual inductance).

Inductance - The property of an electrical component, which opposes the flow of electric current. An inductor has the property of impedance, the opposition to the flow of electric current.

Inductive coupling - A magnetic field transformer between lightning and cables

Interwinding capacitance - Capacitance existing between two wound or coiled wires, such as those found in a transformer.

I/O - Abbreviation for input/output. The term is used to refer to those operations, devices and data-bearing media that are used to pass information into or out of a computer.

Isolation - To cut off the power supply to an installation , or a separate part of it, so that it can safely be worked upon.

Isolator - A mechanical switching device for the purpose of isolation

ITU-T (formerly CCITT): The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. Prior to 1992, it was known as the International Telegraph and Telephone Consultative Committee (CCITT, from the French name "Comité consultatif international téléphonique et télégraphique").