A fuse is an overcurrent protection device. It primarily consists of a fusible element, fuse tube, and additional fillings. When used, the fuse is connected in series with the protected circuit. If the current in the protected circuit exceeds the specified value for a certain period, the heat generated by the fusible element will melt it, breaking the circuit and thus providing protection.

※ What are the components of a fuse?

1.Fusible Element:

This is the core component of the fuse. It cuts off the current when it melts. Fuses of the same type and size should have the same material, geometric dimensions, and resistance values. It's crucial that the characteristics of the fuses remain consistent.

2.Support Structure:

The fusible elements are usually thin and flexible. The support structure's role is to secure the fusible element, making the assembly robust and easy to install and use. It requires good mechanical strength, insulation, heat resistance, and flame retardancy. It should not break, deform, burn, or short-circuit during use.

3.Electrical Contacts:

There are typically two electrical contacts. They are crucial components connecting the fusible element to the circuit and require good conductivity without significant contact resistance.

※ What are the requirements for selecting a fuse?

1. The fuse should not blow during normal operation of electrical equipment.

2. It should blow immediately in case of a short circuit.

3. The fuse should not blow during normal current fluctuations (e.g., motor starting).

4. It should have a time-delay blow during sustained overload conditions.

Fuse selection mainly involves choosing the type and determining the rated current of the fusible element. When selecting a fuse type, consider the protective characteristics of the load and the magnitude of the short-circuit current.

For instance, fuses used to protect lighting and motors primarily consider overload protection. In such cases, a fuse with a lower melting coefficient is preferred. Therefore, smaller capacity lighting circuits and motors are suitable for RC1A series fuses with lead-tin alloy fusible elements. For larger capacity circuits, besides overload protection, the ability to interrupt short-circuit currents should also be considered.

For lower short-circuit currents, fuses with tin-based fusible elements like the RCIA series or zinc-based RM10 series can be used. For workshop low-voltage supply circuits, the ability to interrupt during short-circuits is generally considered. For high short-circuit currents, fuses with high interrupting capacity like the RL1 series should be used. For extremely high short-circuit currents, fuses with limited current capabilities like the RT0 series are recommended.

The rated voltage of the fuse should be equal to or greater than the circuit's rated voltage, and the rated current should be selected based on the load conditions.

For resistive loads or lighting circuits, select a fuse rated at 1 to 1.1 times the load's rated current.

For inductive loads like motors, where the starting current can be 4 to 7 times the rated current, select a fuse rated at 1.5 to 2.5 times the motor's rated current.

※ What are the principles for selecting a fuse?

Select based on the network voltage and short-circuit current.

Fuse selection is generally based on the network voltage and the maximum possible short-circuit current in the distribution system.

Select based on load protection characteristics and expected short-circuit current.

For instance, when protecting lighting and low-power motors, consider their overcurrent protection. In contrast, for larger capacities, focus on short-circuit protection and interrupting capability.

Reasonably select the rated current based on load characteristics.

Devices typically have some overload capacity. Therefore, select a fuse that can handle these transient overloads without blowing prematurely.

※ How to select a fuse?

1.Consider overcurrent selection.

When using fuses in coordination, consider overcurrent selection. This refers to the minimum rated current ratio between the upstream and downstream fuses. The time-current characteristics are closely related, and it usually requires detailed calculations based on manufacturer-provided parameters.

2.Select based on fuse type.

G-class fuses provide overcurrent protection and are primarily used for main distribution lines and cable short-circuit and overcurrent protection. A-class fuses are mainly used for lighting circuits and motor circuits.

Since low-multiple overcurrents cannot be protected by these fuses, they should be used in conjunction with thermal relays or other overcurrent protection devices.