Glossary
AUTO
Method of remote operation of the motor operators via control cables, e.g. PLC.
Breaking capacity
The breaking capacity is the rms value of the current at a specific cos φ (power factor) and a specific voltage which can be safely interrupted by a switching device or fuse under prescribed conditions. The rms value of the symmetrical component applies in the case of alternating current.
I^{2}t characteristic
The I^{2}t characteristic is a curve which represents the minimum or maximum values of I^{2}t in relation to breaking times as a function of the prospective current under defined operating conditions.
I^{2}t value
The I^{2}t value is the thermal value of a prospective or a limited shortcircuit current (letthrough current).
Letthrough current
The letthrough current I_{D} is the maximum instantaneous current value during the breaking time of a switching device or fuse. Limited shortcircuit currents occur if the switching device reduces the amplitude of the shortcircuit current due to, for example, resistance, switching delay and peak arc voltage. The letthrough current of a device such as a currentlimiting fuse or a currentlimiting molded case circuit breaker determines the thermal load (I^{2}t value) imposed on equipment connected downstream of the device (current limiting).
LOCK
Operating mode of motor operators; the operating mechanism is locked and cannot be operated.
Making capacity
The making capacity is the value of the prospective making current which the switching device can safely conduct at the instant of closing under prescribed conditions for a specific circuit.
For molded case circuit breakers, the making capacity is expressed as the maximum possible instantaneous value of the potential prospective current at the input terminals for the specified voltage.
MANUAL
Local, manual operating mode of motor operators.
Protective characteristic
The protective characteristic is determined by the rated operational current and the setting and tripping values of the circuit breaker.
Rated breaking capacity
The rated breaking capacity is the maximum current that can be interrupted by a switching device under certain conditions.
Rated frequency
Design frequency for a switching device and reference value for other characteristics of the device.
Rated making capacity
The rated making capacity is the maximum current that a switching device can conduct at the instant of closing in accordance with the utilization category at the relevant rated operational voltage.
Rated operational current
The rated operational current I_{n} for molded case circuit breakers is equivalent to the rated uninterrupted current I_{U} and to the conventional freeair thermal current I_{th}.
Rated operational voltage
The rated operational voltage U_{e} of a switching device, e.g. a molded case circuit breaker, is the voltage which serves as a reference to state other characteristics of the device. The maximum rated operational voltage must never be higher than the rated insulation voltage.
With multiphase circuits, the specified voltage is generally the phasetophase voltage.
Rated peak withstand current, impulse shortcircuit current
Maximum permissible instantaneous (peak) value of the prospective shortcircuit current in the current path under the highest load. It characterizes the dynamic shortcircuit strength of a switching device.
Rated residual current
The rated residual current I_{Δn} is the fault (residual) current for which residual currentoperated circuit breakers are designed. The residual current rating is declared on the rating plate of the device.
Rated service shortcircuit breaking capacity
The rated service shortcircuit breaking capacity I_{cs} is the shortcircuit current determined by the operational voltage that a molded case circuit breaker is capable of interrupting repeatedly (test sequence 0  C0  CO, formerly P  2). After a molded case circuit breaker has interrupted a short circuit, it can continue to carry the rated operational current despite increased selfheating and will trip again in the event of a short circuit.
Rated shortcircuit breaking capacity
The rated shortcircuit breaking capacity I_{cn} of a molded case circuit breaker is the maximum current that the circuit breaker can safely interrupt at a specific rated operational voltage and rated frequency. It is specified as an rms value.
With AC molded case circuit breakers, the rated shortcircuit breaking capacity must be independent of the magnitude of the DC component. The rated shortcircuit breaking capacity also ensures that the molded case circuit breaker can interrupt every current up to the rated shortcircuit breaking capacity in the event of a linefrequency recovery voltage with 110% of the rated operational voltage.
This applies:

To alternating current at every value of the power factor, but not lower than the value defined in the relevant test specification.

To direct current (unless otherwise specified by the manufacturer) with every time constant, but not greater than the value defined in the relevant test specification.
The shortcircuit breaking capacity does not apply in the event of a recovery voltage at line frequency above 110% of the rated operational voltage.
Rated shortcircuit making capacity
The rated shortcircuit making capacity I_{cm} of a molded case circuit breaker is the maximum current that the circuit breaker can safely interrupt at a specific rated operational voltage and rated frequency. Unlike other characteristic data, this is specified as a peak value.
With AC molded case circuit breakers, the rated shortcircuit making capacity must be at least equal to the rated shortcircuit breaking capacity multiplied by a factor n.
The rated shortcircuit making capacity is calculated to allow the molded case circuit breaker to conduct the current during closing at a voltage of up to 110% inclusive of the rated operational voltage.
Rated shorttime current
Permissible rms value of the AC component of the prospective shortcircuit current which the switching device is capable of conducting for a specific time period, e.g. from 0.05 s to 1 s (thermal shortcircuit strength).
Rated shorttime withstand current
The rated shorttime withstand current I_{cw} is specified as an rms value of the shortcircuit current and characterizes the thermal strength of a circuit of a switchgear assembly under brief load conditions. The rated shorttime withstand current calculation normally refers to a period of 1 s. The reference time must be specified if it deviates from the above. The rated shorttime withstand current is specified for the distribution and/or main busbars of a switchgear assembly.
Rated ultimate shortcircuit breaking capacity
The rated ultimate shortcircuit breaking capacity I_{cu} is the maximum shortcircuit current that a molded case circuit breaker is capable of interrupting (test sequence 0  C0, formerly P  1). After the molded case circuit breaker has cleared the short circuit, it is capable of tripping with increased tolerances under overload conditions.
Limit value of rated ultimate shortcircuit breaking capacity I_{cu}.
Rated ultimate shortcircuit breaking capacity
The rated ultimate shortcircuit breaking capacity I_{cu} is the maximum value of the shortcircuit current which the protective device is capable of disconnecting in accordance with regulations. Up to this value, the protective device is also allowed to be used in a network.
Rated ultimate shortcircuit breaking capacity
The rated ultimate shortcircuit breaking capacity I_{cu} is the maximum shortcircuit current that a molded case circuit breaker is capable of interrupting (test sequence 0  C0, formerly P  1). After the molded case circuit breaker has cleared the short circuit, it is capable of tripping with increased tolerances under overload conditions.
Limit value of rated ultimate shortcircuit breaking capacity I_{cu}.
Rated ultimate shortcircuit breaking capacity
The rated ultimate shortcircuit breaking capacity I_{cu} is the maximum value of the shortcircuit current which the protective device is capable of disconnecting in accordance with regulations. Up to this value, the protective device is also allowed to be used in a network.
Rated uninterrupted current
The rated uninterrupted current I_{U} of a switching device, e.g. a molded case circuit breaker, is a current that the device can conduct in uninterrupted operation (for weeks, months or years). This current is specified by the manufacturer.
Rating
The rating is the power that a switching device is capable of switching at the associated rated operational voltage in accordance with the utilization category, e.g. power contactor utilization category AC3:37 kW at 400 V.
Remote control
Or AUTO; method of remote operation of the motor operators via control cables, e.g. PLC.
Short circuit
Connection with a negligibly low impedance between two points of different potential in an electric circuit. The shortcircuit current is a multiple of the rated operating current. Short circuits can cause thermal or mechanical damage to switching devices and other parts of an electrical installation.
Shortcircuit strength
This is the resistivity of a switching device in the closed state, along with its components (e.g. trip units), or a complete switchboard to the electrodynamic and thermal stresses which arise in the event of a short circuit.
The characteristic for the dynamic stress is the rated peak withstand current, which is the maximum instantaneous value of the shortcircuit current.
The characteristic for the thermal stress of the shortcircuit current is the rootmeansquare value of the shortcircuit current throughout its duration.
Tripping current of overload release
The current value at which a trip unit trips within a specified time.
Tripping current, ground fault
When the ground fault current reaches or exceeds this limit value, the groundfault protection, for example, of a molded case circuit breaker, is tripped.
Tripping current, instantaneous
When this current limit is exceeded, the circuit breaker trips instantaneously.
Tripping current, overload
When this uninterrupted current limit is exceeded within a predefined time period, the circuit breaker trips (inversetime delayed tripping!).
Tripping current, shorttime delayed
When this current limit is exceeded, the circuit breaker trips after a predefined time delay.
Tripping time
Period of time from the instant of commencement of trip command output to the moment at which the command becomes irrevocable (timing concept for the tripping of circuit breakers).