Essential Definitions

Major Markings
Rated voltage Ur
Voltage used in the designation of the fuse-link, from which the test conditions are determined. The rated voltage of the fuse shall be equal or higher than the highest operating voltage, taking into account the switching voltage level and insulation level of the equipments in the circuit.

Rated current Ir
The current assigned to the fuse-link that a new clean fuse-link will carry continuously without exceeding specified temperature rises.

Rated maximum breaking current I1
Maximum value of prospective current that a fuse is capable of breaking under prescribed conditions.

Rated minimum breaking current I3
Minimum value of prospective current that a Back-Up fuse-link is capable of breaking under prescribed conditions of use.

Other Useful Definitions


Current limitation
Interruption of the highest short-circuit currents much before they reach their prospective peak values. This keeps potential damage to an absolute minimum.

Prospective current
Current that would flow in the circuit if a conductor of negligible impedance replaced the fuse.

Cut-off current
Maximum instantaneous value of current attained during the breaking operation of a fuse.

Pre-arcing time (melting time)
Time interval between the beginning of a fault current and the instant of internal arc initiation.

Arcing time
Time interval between arc initiation in a fuse-link and final arc extinction.

Operating time (total clearing time)
total of the pre-arcing time plus arcing time.

Switching voltage
Maximum instantaneous value of voltage, which appears across the terminals of a fuse during operation.

Power dissipation
Power released in a fuse-link carrying a stated value of current under prescribed conditions of use and behaviour.

Derating current
Some of the fuses with high nominal current values are provided with a seperate derating current, which highlights the maximum current that fuse can be loaded on a continous basis.

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