6,3x32 Time Lag 500/440V

Properly fused:
Equipment protection fuses in DC applications:
Is an appliance protection fuse suitable for both AC and DC operation? And what should be considered for overcurrent protection in DC applications?
The problem:
When a short-circuit current flows through a fuse, the fusible conductor inside melts. Depending on the voltage applied and the level of the short-circuit current, an arc is formed here via which the current flow is maintained. This means that the short-circuit lasts longer than intended. In alternating current applications (AC), the arc is extinguished again with the help of the zero crossing of the current.
In a direct current (DC) application, however, this zero crossing is missing •the consequence:
The arc can stop between the two fuse caps when the permissible DC rated voltage is exceeded, burn holes in them or cause the fuse body to burst. Metallised material then escapes from the inside of the device protection fuse, which in an emergency can cause new short circuits and thus charring on the circuit board and, in the worst case, a fire.
Suitable for direct currents:
The actual behaviour of G-fuses when switching off DC currents depends on their design and characteristics.
•There is a wide selection for use with extra-low voltages up to about 65V DC. The reason: in this voltage range, only low-energy arcs occur, so safe operation is possible even with very small designs.
•For voltages above 100V, fuses with a ceramic body and corresponding filling are usually used. At which driving voltage these properly switch off depends on the size, material, rated current and characteristics.
•Superfast (FF) fuses are often suitable for high DC voltages, as they are designed for pure short-circuit protection.
•Slow-blow (T) fuses of the same design do not come close to achieving these values. Influence on breaking capacity Level of DC voltage: For certain products, the DC rated voltage is given with a higher value than the AC rated voltage. Why? A DC rated G-fuse can extinguish the arc, but in an AC application it is loaded with the peak value. Thus, the peak voltage values play a major role. Time constant of the short-circuit circuit: The greater the time constant, the lower the value of the DC voltage for the use of the G-fuse link. The time constant is determined from L/R, taking into account the reactances of the components located in the short-circuit branch. In most applications, the time constant is no more than 10ms, in battery circuits less than 3ms.
•This means that time constants of around 100ms can lead to the value of the rated AC voltage having to be reduced by more than 50% for use in the DC voltage circuit.
•The maximum DC voltage, on the other hand, can be higher than the rated AC voltage (rms value) of the G-fuse link due to the oscillation behaviour in the DC link of a frequency converter. Tip: Performance behaviour of G-fuses The performance of the equipment protection fuses from the manufacturer SIBA varies greatly depending on the design.
In the dimensions 6.3x32mm, they can be used for short-circuit protection at up to 1000V DC even at low rated currents. Areas of application G-fuses are typically used in the DC circuits of emergency power supplies and emergency lighting systems.
While the systems are operated with a mains voltage of 230V AC in normal operation, a fuse that can safely switch off direct currents is required for emergency power operation and supply by a powerful central battery.
Since this cannot be replaced when required, it must be designed for both DC and AC operation. In addition, to avoid damage, the level of the possible short-circuit current must be taken into account here, which can be 6,000A and more.
Not every fuse is capable of properly disconnecting such a high direct current.