Fuse Design and Selection Points

Ⅰ. The Working Principle and Use of the Fuse

A fuse, also known as a fuse, is an electrical protection component used in a circuit to ensure the safe operation of a circuit.

Figure. 1

When a circuit malfunctions or behaves abnormally, the current keeps rising. This rising current may harm some significant and pricey circuit components, or it may burn the circuit and start a fire. If the fuse is correctly positioned in the circuit, it will automatically explode when the aberrant current gets to a particular height, protecting the circuit's safe operation. The fuse is connected in series to the circuit, so it typically needs to have low resistance. The fuse is similar to a wire and can be used for a long time when the circuit is operating normally.

Ⅱ. Fuse-Related Parameters and Selection Reference

Determine the number of amps of fuse you require by multiplying the electrical power consumed by the current (current = electrical power/voltage). A 2.5A fuse should be chosen since, for instance, a 500W appliance's voltage is 220V and 500/220=2.27.

The fuse's copper head is engraved with information like "F5AL 250V," indicating that it is a 5A fuse. A 5A fuse can handle current up to 5 amps. A fuse with a 5x20 standard has a tube that is 5 mm in diameter and 20 mm in length.

Voltage Rating: The fuse's voltage rating must be more than or equal to the circuit's maximum voltage. Standard rated voltages are typically 32, 63, 125, 250, and 600V.

Fuses respond more readily to changes in current than voltage. A fuse can be used at any voltage lower than its rated voltage because it maintains its original shape at any voltage between zero and its maximum rating.

Current Rating: The fuse's current carrying capacity is indicated by the fuse's current rating. the nominal maximum current at which the fuse can operate without tripping. 0.5A, 1A, 2A, 3A, 4A, 5A, 6A, 8A, 10A, 15A, and 20A are typical ones.

Fusing current: The fuse blows to protect the following circuit when the circuit's current reaches or exceeds the current value. The fusing current is typically between 1.1 and 1.3 times its rated current. The rated current is exceeded by the fusing current. A fuse, for instance, can function normally when the flow through it is less than its rated current of 5A. The fuse blows to open the circuit and protect it once it reaches 5A or even more. The standard in our nation mandates that a fuse's fusing current be double that of its rated current.

Breaking capacity: Under rated voltage, the fuse's breaking capacity is the highest current value at which the circuit can be safely disconnected without harm. The greatest possible fault current in the circuit must be equal to or greater than the breaking capacity of the fuse. The fuse may break or explode, posing a threat, when the instantaneous overload current within exceeds the rated value.

Characteristics of the surge and pulse currents: When the power is first turned on, the majority of circuits experience an instantaneous surge current. This surge current is frequently many times, if not dozens of times, bigger than the typical steady-state current in capacitive or inductive circuits. Fuse withstand surge current is occasionally a crucial connection in the circuit design. Although the pulse current may harm the fuse and shorten its life, it need not necessarily break the fuse.

Voltage drop: This term, which describes the voltage drop across the fuse under the conditions of rated current, indicates the internal resistance of the fuse, and its value ought not to be excessive. The system characteristics of the circuit will be impacted and the circuit won't be able to function correctly if a fuse with an excessively high internal resistance is inserted in the circuit. The fuse's resistance should be as low as possible so that the power loss of the fuse is also minimal. Be mindful of the impact of resistance while choosing small-sized fuses.

Ambient temperature: The fuse's life will be shortened and its operating temperature will increase with a higher ambient temperature. On the other hand, operating at lower temperatures will increase the fuse's lifespan. As a result, the rated current of the fuse should be changed in accordance with the temperature of the fuse's actual operating environment.

Time-current curve: refers to one of the most crucial fuses' parameters. The fuse blows when the amount of electricity flowing through it is greater than its rated current. A fuse's time-current characteristic describes how to overload current and fusing time interact.

Figure. 2

Dimensions: Dimensions are in millimeters. Commonly used tubular fuses have dimensions of Φ6X30, Φ5X20, Φ3X10, and Φ2X7.

Purely resistive circuits, where the surge is minimal, or circuits that must safeguard certain particularly delicate and priceless components, require the usage of quick fuses. When turning on and off, capacitive or inductive circuits experience a surge, necessitating the usage of a slow-blow fuse.

Figure. 3

Figure. 4 Fuse Holder for Mounting Fixed Mount Fuses

Ⅲ. Common Causes of Blown Fuses

1. The circuit has a short circuit, and the short circuit current is too great to cause the fuse to explode.

2. The loop fuse is blown because the load power is too high and the current rises, which is greater than the fuse's capacity to handle the current regularly.

3. The voltage is unstable, and the electrical device's power fluctuates often, which causes frequent fluctuations in the current flowing through the fuse and the fuse's eventual blowing.

4. The fuse itself is worn out and has been in use for too long. Because the fuse has a specific resistance, when the current warms up, the resistance increases, and the fuse eventually blows because the resistance becomes too high.

5. The fuse has been oxidized after being in the air for a long time.