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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.

I2t characteristic

The I2t characteristic is a curve which represents the minimum or maximum values of I2t in relation to breaking times as a function of the prospective current under defined operating conditions.

I2t value

The I2t value is the thermal value of a prospective or a limited short-circuit current (let-through current).

Let-through current

The let-through current ID is the maximum instantaneous current value during the breaking time of a switching device or fuse. Limited short-circuit currents occur if the switching device reduces the amplitude of the short-circuit current due to, for example, resistance, switching delay and peak arc voltage. The let-through current of a device such as a current-limiting fuse or a current-limiting molded case circuit breaker determines the thermal load (I2t 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 In for molded case circuit breakers is equivalent to the rated uninterrupted current IU and to the conventional free-air thermal current Ith.

Rated operational voltage

The rated operational voltage Ue 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 multi-phase circuits, the specified voltage is generally the phase-to-phase voltage.

Rated peak withstand current, impulse short-circuit current

Maximum permissible instantaneous (peak) value of the prospective short-circuit current in the current path under the highest load. It characterizes the dynamic short-circuit strength of a switching device.

Rated residual current

The rated residual current IΔn is the fault (residual) current for which residual current-operated circuit breakers are designed. The residual current rating is declared on the rating plate of the device.

Rated service short-circuit breaking capacity

The rated service short-circuit breaking capacity Ics is the short-circuit 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 self-heating and will trip again in the event of a short circuit.

Rated short-circuit breaking capacity

The rated short-circuit breaking capacity Icn 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 short-circuit breaking capacity must be independent of the magnitude of the DC component. The rated short-circuit breaking capacity also ensures that the molded case circuit breaker can interrupt every current up to the rated short-circuit breaking capacity in the event of a line-frequency 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 short-circuit breaking capacity does not apply in the event of a recovery voltage at line frequency above 110% of the rated operational voltage.

Rated short-circuit making capacity

The rated short-circuit making capacity Icm 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 short-circuit making capacity must be at least equal to the rated short-circuit breaking capacity multiplied by a factor n.

The rated short-circuit 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 short-time current

Permissible rms value of the AC component of the prospective short-circuit current which the switching device is capable of conducting for a specific time period, e.g. from 0.05 s to 1 s (thermal short-circuit strength).

Rated short-time withstand current

The rated short-time withstand current Icw is specified as an rms value of the short-circuit current and characterizes the thermal strength of a circuit of a switchgear assembly under brief load conditions. The rated short-time 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 short-time withstand current is specified for the distribution and/or main busbars of a switchgear assembly.

Rated ultimate short-circuit breaking capacity

The rated ultimate short-circuit breaking capacity Icu is the maximum short-circuit 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 short-circuit breaking capacity Icu.

Rated ultimate short-circuit breaking capacity

The rated ultimate short-circuit breaking capacity Icu is the maximum value of the short-circuit 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 short-circuit breaking capacity

The rated ultimate short-circuit breaking capacity Icu is the maximum short-circuit 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 short-circuit breaking capacity Icu.

Rated ultimate short-circuit breaking capacity

The rated ultimate short-circuit breaking capacity Icu is the maximum value of the short-circuit 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 IU 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 AC-3:37 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 short-circuit 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.

Short-circuit 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 short-circuit current.

The characteristic for the thermal stress of the short-circuit current is the root-mean-square value of the short-circuit 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 ground-fault 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 (inverse-time delayed tripping!).

Tripping current, short-time 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).