Impedance - The obstruction to the flow of current in an ac circuit. The transformer impedance is made up of the internal resistance and reactance which creates a voltage drop caused by current flowing in the windings. Impedance losses are a combination of heat (I2R) losses in the conductor, eddy current loss, and losses in other parts of the transformer caused by stray currents.
Impulse - A current surge.
Impulse Tests - Tests which ensure a satisfactory level of insulation and the ability of a device to withstand, within certain limits, overvoltage surges (such as lightning strikes) that may occur in service.
Indicating Switch - see definition for Switch.
Industrial Establishment - A building or part of a building (other than office or exhibit space) or a part of the premises outside of the building where persons are employed in manufacturing processes or in the handling of material, as distinguished from dwellings, offices, and like occupancies.
Inrush Current - The initial momentary surge current demand before a load resistance of impedance increases to its normal operating value.
Inrush Restraint - A restraint feature that can make the fault indicator inoperable to inrush currents.
Inspection Department - An organization legally authorized to enforce this Code and having jurisdiction over specified territory.
Inspector - Any person duly appointed by the inspection department for the purpose of enforcing Code.
Insulated - Means separated from other conducting surfaces by a dielectric material or air space having a degree of resistance to the passage of current and to disruptive discharge sufficiently high for the condition of use.
Insulating as Applied to Non-Conducting Substances - Means that they are capable of bringing about the condition defined as insulated.
Insulation - A material having a high resistance to the flow of electric current; insulation over underground conductor is made of either EPR or XLPE material.
Insulation Coordination - The review of the protective level of the arrester and the insulation level of the equipment to be protected to ensure that the arrester is adequately protecting the equipment.
Insulation System - A balanced combination of materials (kraft paper, oil, porcelain, etc.) which provides dielectric strength to a device.
Insulator - Any material which does not allow electrons to flow through it.
Intermittent Duty - see definition for Duty.
Interrupter - An element designed to interrupt specific currents under specified conditions.
Interrupter Switch - An air switch, equipped with an interrupter, for making and/or breaking specified currents. NOTE: The nature of the current made or broken, and/or both, may be indicated by suitable prefix; that is, load interrupter switch, fault interrupter switch, capacitor current interrupter switch, etc.
Intrinsically Safe - Means that any spark or thermal effect that may occur in normal use, or under any conditions of fault likely to occur in practice, is incapable of causing an ignition of the prescribed flammable gas, vapour, or dust.
Isolating Switch - see definition for Switch.
Isolation Link - A small metal link used in series with a Bay-O-Net link or MagneX interrupter. During transformer failure, the isolation link will melt so the opened primary circuit of a faulted transformer cannot be re-energized by the line crew. An isolation link has melt characteristics, but no fault clearing capabilities.
|Source: Canadian Electrical Code and National Electrical Code|