´International Electrotechnical Commission. Established in 1906 to deal with questions related to international standardization in the electrical and electronic engineering fields. The members of the IEC are the national committees, one for each country, which are required to be as representative as possible of all electrical interests in the country concerned. Most of them are recognized and supported by their governments.

The Institute of Electrical and Electronic Engineers. An industry organization which, among other things, wrote "Standard 519: IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems".

Insulated-gate bipolar transistor. A special type of bipolar transistor that can turn on and off much more rapidly than conventional bipolar transistors. Like a FET, an IGBT is voltage-operated.

A measure of a circuit’s opposition to the flow of alternating current. This depends on the resistance, capacitance and inductance of the circuit as well as the frequency of the AC voltage.

(transformer) A measure of the voltage regulating ability of a transformer. This is expressed in percent. A transformer with an impedance of 5% will decrease its output voltage by 5% if its output load is increased from no load to full load. The short circuit ratio can also be used to indicate the impedance of a transformer.

induced current
Current which flows in a conductor because of a changing magnetic or electric field.

The measure of the electrical effect of an inductor. This is usually expressed in microhenries (mH) or millihenries (mH).

A coil used in an electrical circuit. An inductor creates a magnetic field that tends to resist changes in the current flowing through it. Its value is often measured in microhenries (mH) or millihenries (mH) and it is also rated by the maximum amount of current it can handle. Because they limit abrupt changes in current, inductors are often used in electrical line noise filter circuits.

A measure of a body’s resistance to changes in velocity. For linear motion, this is measured by the object's mass. For rotational motion, the moment of inertia (WK2) is the product of the weight (W) of an object and the square of the radius of gyration (K2). The radius of gyration is a measure of how the mass of the object is distributed about the axis of rotation. WK2 is usually expressed in units of kg-m2  or lb-ft2.

circuit breakers Input circuit breakers may be used for the drive, the bypass or both. Circuit breakers may not trip quickly enough to protect the drive, but may be supplied if specified.

input contactor
An input contactor provides a selector switch and contactor in the drive enclosure that will electrically disconnect the drive from the line.

input disconnect switch
This switch is installed in the drive enclosure or auxiliary enclosure and disconnects the drive from the power line. This allows the drive to be worked on safely. It should not be used as the means to start and stop the drive.

input follower
Circuitry in the drive that allows it to accept, process and act upon a signal sent to it from elsewhere in the system. Typically the signal is to control the speed of the drive. This allows the drive to automatically "follow" the signal and provide the speed the system demands.

input fusing
Input fusing may be used for the drive, the bypass or both. The "fused power disconnect" may be supplied to meet the requirement for bypass fusing or fuses alone may be supplied.

integrated circuit
A circuit made from transistors, resistors and other components. All are placed in a package referred to as a "chip". All circuits are on one piece of semiconductor material.

interlocks (electrical)
Electrical contacts which are used to govern succeeding operations of the same or related devices. For example: A drive may be connected to an external drive safety interlock switch which stops the drive in emergency situations. Drives also may include a fault relay whose contacts interlock with other equipment, stopping this equipment in case of a drive fault.

interlocks (mechanical)
Mechanical devices that physically prevent certain actions from occurring. For example: A drive disconnect may interlock with the enclosure door, preventing it from being opened when the disconnect is in the on position. Bypass contactors may be mechanically interlocked to ensure that the motor cannot be connected to both the line and drive at the same time.

interrupting capacity
The maximum value of current that a contact assembly is required to successfully interrupt at a specified voltage for a limited number of operations under specified conditions.

The output portion of an adjustable frequency drive. This converts the DC bus into an output AC whose frequency is controlled by the drive’s control circuity. The name "inverter" has also been used to describe the entire adjustable frequency drive.

The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies from some 130 countries, one from each country. ISO is a non-governmental organization established in 1947. The mission of ISO is to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological and economic activity.

ISO's work results in international agreements which are published as International Standards.

isolation transformer
A transformer that electrically separates the drive from the AC power line. It gives some protection to the semiconductors of the drive from line voltage transients and other line disturbances.