Slow-speed Fuses And Drop-out Fuses: What Do These Two Types Of Devices Have In Common?

In the field of power protection, different types of fuses are often discussed separately due to differences in appearance and application scenarios. However, in reality, slow-speed fuses (gG type) and drop out fuse unit have a common working mechanism in their underlying logic, which is the part that is truly worth understanding when making a selection.

Both rely on "thermal effect" to trigger action

The core protection of both is based on the principle of current thermal effect. When the current flowing through the fuse exceeds the rated value, the fuse temperature continues to rise, eventually melting at the weakest point, and the circuit is immediately broken. This process does not rely on any external control signals; it is a purely physical response. After the drop out type fuse fuse melts, the fuse tube falls rapidly under its own weight, forming a visible break point; the slow-speed fuse completes the same thermal melting process inside the casing, with the same principle path.

Inverse-time characteristic: The larger the current, the faster the action

This is another important characteristic shared by both types of fuses—inverse-time protection.

• Under small overload conditions: The fuse heats up slowly, and the melting time is relatively long, giving the equipment a certain tolerance margin.

• In the event of a severe short circuit: the current increases dramatically, heat concentrates rapidly, and the fuse cuts off the circuit in a very short time.

The dropout fuse of transformer fuse in 10kV distribution lines relies on this characteristic to achieve graded response to overload and short circuit. Slow-speed fuses (class G) also provide full-range protection; neither is a simple "either stop or immediately disconnect" switch.

Connected in series, replacing the fuse restores power.

Both are embedded in the protected circuit in series. Once the fuse blows, power is interrupted. To restore power, a fuse of the same specification must be replaced before it can be put back into service. This differs from circuit breakers, which can be directly reset—a blown fuse is "used and then stopped," and the cause of the fault must be investigated before replacement.

Regarding the expulsion drop out fuse fuse, one operational detail is worth noting:

• When replacing the fuse, it must be tightened to the standard tension (approximately 24.5N).

• The fuse element's tilt angle should be maintained at approximately 25°. A loose angle or incorrect installation may cause the contacts to overheat or prevent the fuse element from dropping properly.

• New fuse elements must be standard products with a fusing strength capable of withstanding a tensile force of 147N or more.

Understanding these commonalities is not only for differentiating products, but also for quickly identifying the root cause of faults and making correct protection configuration decisions when facing real-world engineering problems.