Fuses are important components in AC and DC electrical circuits. They protect devices from critical damage. They also defend against possible fire in higher power applications. It is important to use the correct fuse. While AC and DC fuses look the same, there are significant differences to consider.
The most apparent difference between AC and DC fuses is the size.
A property of AC voltage is that it alternates between positive and negative at a rate of 60 cycles per second (Hz). Stopping Alternating Current is relatively easy since it reaches 0 volts 60 times per second. Therefore, the space between the electrodes of an AC fuse does not need to be as great to stop current flow when the fuse blows.
Due to the nature of Direct Current, it can be difficult to interrupt its flow. DC is always positive. It tends to arc between conductors if there is an attempt to create an open circuit. The space between electrodes in DC fuses is greater than in AC fuses. If the metallic wire in the fuse melts due to over current, the current is unable to arc from one electrode to the other. This requires the DC fuse to be longer than an equivalent AC fuse.
Fuses are classified into several categories. The main categories are AC, DC, Low Voltage, and High Voltage.
Most DC fuses are considered Low Voltage fuses. They range from the millivolt range up to 600 volts. Electronic devices are the typical application of millivolt level fuses. The most well-known low voltage fuses are 12, 24, and 48-volts. Vehicles and other mobile equipment are the typical application of these voltages. The fuse element in LV fuses is made of copper, aluminum, or lead. Some Low Voltage fuses can be used in both DC and AC applications. The application voltage can not exceed the fuse volt rating.
Application of High Voltage AC fuses can exceed 100,000 volts and 300,000 amps. Fuses rated for such high-power applications are quite sophisticated. They often contain materials or gasses that can help extinguish an arc when the fuse blows. The fuse elements used in HV fuses are usually copper, silver, or tin.
3- Suppression Elements
The potential for an arc to form must be suppressed when a fuse blows. In low power applications, air space is usually sufficient. The electrodes at the ends of the fuse are far enough apart that the current will not span the gap. In higher power DC applications, an insulator must be inserted between the electrode to break the current flow. Silica or some other insulating material is placed between the electrodes of a Low Voltage fuse. When the fuse overheats, the material melts and forms a barrier between the electrodes. In High Voltage AC applications, gasses or liquid chemicals are stored inside the fuse. When the fuse element fails, the liquid or gas will suppress the potential arc.