How to Select and Use Fuses: Key Considerations
1. Voltage Ratings
The fuse's voltage rating must be greater than or equal to the maximum voltage of the circuit it is intended to interrupt. Since a fuse has very low resistance, its voltage rating becomes critical only when the fuse attempts to blow. Once the fuse element melts, the fuse must be capable of rapidly breaking the circuit, extinguishing the arc, and preventing the open-circuit voltage from re-igniting an arc across the gap.
2. Current Ratings
The current rating indicates the fuse's current-carrying capacity under a specific set of test conditions. Every fuse is marked with a current rating, which may be represented by a number, a letter, or a color code. The meaning of each marking can be found in the product datasheet.
3. Breaking Capacity (Interrupting Rating)
A fuse must be able to interrupt a faulty circuit without damaging the surrounding circuitry. Breaking capacity refers to the maximum current a fuse can safely interrupt at its rated voltage without sustaining damage. The fuse's breaking capacity must be equal to or greater than the maximum potential fault current in the circuit.
4. Melting Integral
The melting integral represents the energy required to melt the fuse element; it is also known as the melting value, or $I^2t$. This value is determined by the structure, material, and cross-sectional area of the fuse element. Since different fuse series utilize varying materials and element configurations based on their current ratings, it is essential to determine the specific $I^2t$ value for each fuse.
In DC circuits, a fault current equal to ten times the rated current is typically used to cause the fuse to blow within an extremely short time, allowing for the measurement of highly precise I²t values using a high-speed oscilloscope and an integration procedure.
I. Functions of a Fuse
1. Under normal conditions, the fuse serves to complete the circuit.
2. Under abnormal (overload) conditions, the fuse acts as a safety protection component; it melts to safely cut off the current and protect the circuit.
II. Precautions for Fuse Usage
1. Fuses must be connected in series with the circuit, installed vertically, and placed on each phase line; installing a fuse on the neutral line of a two-phase three-wire or three-phase four-wire circuit is prohibited.
2. For screw-type fuses, the incoming power line should be connected to the center terminal of the base, and the outgoing line to the threaded shell; these fuses are suitable for use in locations subject to vibration.
3. Tubular fuses should be used for power loads exceeding 60A, or for lighting/electric heating loads (220V) exceeding 100A.
4. Control fuses should be installed for electricity meter voltage circuits and electrical control circuits.
5. Porcelain plug-in fuses must use certified lead-alloy or copper wire; do not substitute a single large fuse with multiple strands of thinner fuse wire.
6. Fuses must be intact and undamaged, with tight and reliable contact. Inspect contact conditions and check for discoloration, deformation, or aging during the maintenance of power distribution equipment; replace the fuse if necessary.
7. After selecting a fuse, verify that it provides adequate protection for the conductors. If the conductor cross-section is too small, it should be increased appropriately.
8. For drop-out fuses, the copper cap must engage at least three-quarters of the upper contact on the fuse tube, and the surface of the fuse tube or fuse element must be free of damage or cracks.
9. Fuse ratings must not be arbitrarily increased, nor should copper or aluminum wires be used as substitutes.
The fuse's voltage rating must be greater than or equal to the maximum voltage of the circuit it is intended to interrupt. Since a fuse has very low resistance, its voltage rating becomes critical only when the fuse attempts to blow. Once the fuse element melts, the fuse must be capable of rapidly breaking the circuit, extinguishing the arc, and preventing the open-circuit voltage from re-igniting an arc across the gap.
2. Current Ratings
The current rating indicates the fuse's current-carrying capacity under a specific set of test conditions. Every fuse is marked with a current rating, which may be represented by a number, a letter, or a color code. The meaning of each marking can be found in the product datasheet.
3. Breaking Capacity (Interrupting Rating)
A fuse must be able to interrupt a faulty circuit without damaging the surrounding circuitry. Breaking capacity refers to the maximum current a fuse can safely interrupt at its rated voltage without sustaining damage. The fuse's breaking capacity must be equal to or greater than the maximum potential fault current in the circuit.
4. Melting Integral
The melting integral represents the energy required to melt the fuse element; it is also known as the melting value, or $I^2t$. This value is determined by the structure, material, and cross-sectional area of the fuse element. Since different fuse series utilize varying materials and element configurations based on their current ratings, it is essential to determine the specific $I^2t$ value for each fuse.
In DC circuits, a fault current equal to ten times the rated current is typically used to cause the fuse to blow within an extremely short time, allowing for the measurement of highly precise I²t values using a high-speed oscilloscope and an integration procedure.
I. Functions of a Fuse
1. Under normal conditions, the fuse serves to complete the circuit.
2. Under abnormal (overload) conditions, the fuse acts as a safety protection component; it melts to safely cut off the current and protect the circuit.
II. Precautions for Fuse Usage
1. Fuses must be connected in series with the circuit, installed vertically, and placed on each phase line; installing a fuse on the neutral line of a two-phase three-wire or three-phase four-wire circuit is prohibited.
2. For screw-type fuses, the incoming power line should be connected to the center terminal of the base, and the outgoing line to the threaded shell; these fuses are suitable for use in locations subject to vibration.
3. Tubular fuses should be used for power loads exceeding 60A, or for lighting/electric heating loads (220V) exceeding 100A.
4. Control fuses should be installed for electricity meter voltage circuits and electrical control circuits.
5. Porcelain plug-in fuses must use certified lead-alloy or copper wire; do not substitute a single large fuse with multiple strands of thinner fuse wire.
6. Fuses must be intact and undamaged, with tight and reliable contact. Inspect contact conditions and check for discoloration, deformation, or aging during the maintenance of power distribution equipment; replace the fuse if necessary.
7. After selecting a fuse, verify that it provides adequate protection for the conductors. If the conductor cross-section is too small, it should be increased appropriately.
8. For drop-out fuses, the copper cap must engage at least three-quarters of the upper contact on the fuse tube, and the surface of the fuse tube or fuse element must be free of damage or cracks.
9. Fuse ratings must not be arbitrarily increased, nor should copper or aluminum wires be used as substitutes.
Aug 12,2026