Learn the advantages and disadvantages of fuse in electrical circuits. Learn how fuses provide cost-effective protection but may lead to downtime due to single-use design.
What is a fuse?
Fuse safeguards electrical devices from overloads and short circuits. It disconnects the electrical circuit under short circuit or overload currents.
It protects against overloads and short circuits at up to 66 kV and 400 kV. It is only used in applications where its performance is suitable for interrupting the current. A Fuse is the cheapest protection device that protects the electrical circuit in the event of short circuits and overloading of circuits.
The working of the fuse is based on the heating effect of the current(I2R). It allows normal current to flow through it and generates heat in the fuse element. The surrounding air dissipates this heat and keeps the fuse’s temperature below its melting point.
During a fault, a short-circuit current passes through the fuse element. This current is significantly higher than the normal current. The high current causes the fuse element to heat up rapidly and melt. As a result, the fuse interrupts the circuit, stopping the flow of short-circuit or overload current.
The fuse element is made from a high-quality metal conductor. It is enclosed within a cartridge. Under normal conditions, the element allows current to flow through it. However, when a high-magnitude current flows, the fuse element melts and breaks the electrical circuit to prevent damage.
Advantages of Fuse
- Fuses are the most cost-effective method of protection.
- The fuse element can be easily replaced.
- The fuse is completely maintenance-free.
- In the event of a short circuit, it breaks the short circuit current flow.
- Compared to circuit breakers, their operation is entirely automatic, they are faster, and no complication is involved in any part of it
- A majority of fuses have built-in safety mechanisms, including the ability to extinguish electrical arcs.
- The fuses with smaller elements can limit the current flowing through the circuit during a short circuit.
- It is used for overload protection because of its inverse time-current relationship.
- A fuse can interrupt a large short circuit current without generating noise, flames, or smoke.
- Easy to remove and replace without risk of damage from contact with an active component in the circuit.
- The smaller fuse elements limit the current under short-circuit conditions.
- A fuse operates significantly faster than a circuit breaker. It provides primary protection against electrical short circuits.
- It takes only a few milliseconds (0.002 seconds) to interrupt the circuit during a failure.
- Compared to other switchgear protection devices, it has a more compact design and it is easy to transport and operate.
- It acts as a barrier between the human body and the electric circuit.
- Protects devices from failure caused by incorrect circuit operation.
- It prevents damage caused by improperly connected loads.
Disadvantages of Fuse
- It is not designed to handle overloads, and if one occurs, replacing the fuse can be time-consuming, leading to a power outage during the process.
- The protection offered by the fuse can not be reliable.
- It has a low breaking capacity.
- Compared to circuit breakers, fuses operate at a much slower speed.
- A circuit breaker can be reset and used multiple times, whereas replacing a fuse after it operates takes a significant amount of time.
- When a motor is started, the fuse is unable to withstand the surge current.
- The fuse can’t protect the circuit against under-voltage.
- Since the fuse element responsible for fusing is exposed to air, it may gradually oxidize over time.
- As a result, the element’s resistance increases, leading to greater heat generation from the current passing through it.
- If the fuse wire is of the incorrect size, it may need to be replaced frequently.
- Fuses do not have adjustable trip settings.
- Fuses can degrade over time and may cause nuisance tripping
- It is not always easy to correlate the time-current characteristics of a fuse with those of the protective device.
- When fuses are connected in series, it becomes difficult to discriminate between them unless there is a substantial size difference in fuses. Even with a noticeable size difference in fuses, it is difficult to discriminate them.
- Since the fuse is designed to respond only to current flow and not high voltage, it is unlikely to melt or protect the house from damage in the event of a direct lightning strike.
- Accurate calibration of fuse wires is difficult because a longer fuse wire tends to blow faster than a shorter one under the same conditions.
- It is recommended not to use a fuse in circuits with a high voltage rating.
- Fuses are single-use and must be replaced after blowing, which can raise operating costs and cause increased downtime.
In primary distribution systems, fuses are used to protect transformers with ratings up to 200 KVA, and cables in low-voltage light and power circuits that operate at low voltages. They are preferred in low or moderate-voltage applications where frequent operation is not required, or where using a circuit breaker would be uneconomical, fusses are preferred instead of circuit breakers.