Usage and Maintenance of Fuses

Use and Maintenance

In low-voltage power distribution systems, fuses are protective electrical devices. Widely used for power grid and electrical equipment protection, fuses automatically cut off circuits when short circuits or overloads occur in the grid or equipment, preventing damage to electrical devices and preventing accidents from spreading.

A fuse consists of an insulating base (or support), contacts, and a fuse element. The fuse element is the primary working component, acting like a special conductor connected in series within the circuit. When a short circuit or overload occurs in the circuit, the excessive current causes the fuse element to overheat and melt, thereby interrupting the circuit. Fuse elements are typically made in wire, grid, or strip forms. The materials used for fuse elements have relatively low melting points, stable characteristics, and are easily fusible. Common materials include lead-tin alloys, silver-plated copper strips, zinc, silver, and other metals.

An electric arc is generated when the fuse element melts and interrupts the circuit. To safely and effectively extinguish this arc, the fuse element is generally installed within a fuse housing, where measures are taken to rapidly quench the arc.

Fuses have advantages such as simple structure, ease of use, and low cost, making them widely used in low-voltage systems.

Precautions

(1) Precautions for Using Fuses:

• The protective characteristics of the fuse should match the overload characteristics of the protected object. Consider potential short-circuit currents and select a fuse with the appropriate interrupting capacity.
• The rated voltage of the fuse must be suitable for the line voltage level. The rated current of the fuse must be greater than or equal to the rated current of the fuse element.
• The rated currents of fuse elements at various levels in the circuit must be properly coordinated, ensuring that the rated current of the upstream (preceding) fuse element is greater than that of the downstream (next) fuse element.
• Fuse elements must be used according to specified requirements. It is not allowed to arbitrarily increase the size of the fuse element or substitute it with other conductors.

(2) Fuse Inspection and Patrol:

• Check whether the rated values of the fuse and fuse element are compatible with the protected equipment.
• Inspect the fuse's appearance for any damage or deformation, and check the porcelain insulation for any signs of flashover or discharge.
• Check all contact points of the fuse to ensure they are intact, tightly connected, and free of overheating.
• Check whether the fuse's fault indication device is functioning normally.

(3) Fuse Use and Maintenance:

• When a fuse element melts, carefully analyze the cause. Possible reasons include:
  • Normal melting due to a short circuit or overload.
  • Incorrect melting due to prolonged use, oxidation of the element, or high operating temperatures altering the element's characteristics.
  • Mechanical damage during installation, reducing the cross-sectional area and causing incorrect melting during operation.
• When replacing a fuse element, ensure the following:
  • Before installing a new element, identify the cause of the previous melting. Do not replace the element and attempt to re-energize the circuit without determining the cause.
  • When replacing the element, verify that its rated value matches the protected equipment.
  • When replacing the element, inspect the inside of the fuse tube for burn damage. If severe burning is found, replace the fuse tube as well. If a porcelain fuse tube is damaged, it must not be replaced with a tube made of other materials. When replacing the element in a filled-type fuse, pay attention to refilling the filler material properly.
• Fuses should be maintained together with the associated switchgear:
  • Clean dust and inspect the condition of contact points.
  • Inspect the fuse's appearance (after removing the fuse tube) for damage, deformation, and check the porcelain components for discharge or flashover marks.
  • Verify that the fuse and its element are properly matched to the protected circuit or equipment, and make adjustments promptly if any issues are found.
  • Pay special attention to ensure that fuses are not used in the N-line of TN grounding systems or in equipment grounding protection lines.
  • When maintaining or inspecting fuses, follow safety regulations by disconnecting power. It is not permitted to remove the fuse tube while the circuit is energized.