Amidst the increasing competition in the market for electronic product prices, some manufacturers have replaced fuse components with resistors. Since resistors have a certain load limit, this means that if the current flowing through the resistor exceeds this limit, it can be burned out, presenting an open-circuit condition. In this sense, resistors have a similar function to fuses, as they can interrupt the current in the event of an overcurrent in the circuit. It seems that they can achieve the same effect as fuses. Therefore, some manufacturers have replaced the original fuses with cheaper resistive fuses to reduce costs, but this method does carry risks.
It is made by applying a carbon film coating to a solid ceramic tube using vacuum spraying technology, then machining the outer layer of the carbon film into a spiral pattern. The resistance value is determined by the number of spirals, and a protective film is applied on the outer layer.
We understand that a good fuse must possess three functions: circuit-breaking protection, surge resistance, and safe disconnection. However, a fuse resistor cannot fully perform well in all three aspects.
1. The fuse protection function includes overload protection and short-circuit protection. That is, when the circuit experiences an unpermitted overcurrent up to the limit of short-circuit overcurrent, the fuse must trip within the specified time frame to protect the circuit or component. However, due to the structure of the fuse resistor mentioned above, which only has a carbon film conductor coated on the surface, it cannot achieve the same accuracy as a fuse for parameters such as fuse trip time and long-term continuous power-on time. Therefore, overload current protection cannot be guaranteed, and it can only have a slight effect on short-circuit current.
2. The surge resistance function is guaranteed by the melting thermal energy value I2t, allowing the fuse to withstand a certain amount of energy from pulse shocks equivalent to a normal number of switching cycles. We need to calculate and evaluate this during selection, as the fuse resistance itself does not have a similar I2t technical specification. Using it too small can lead to being broken by the pulse shock, while using it too large offers little protective function.
3. Safety features are ensured through standard specifications such as rated voltage and breaking capacity, particularly by obtaining internationally recognized third-party safety certifications. However, the fuse itself is not a safety component and does not require safety certification. Its safety is self-evident, as its protective function is inherently insufficient, and it is difficult to guarantee that no hazardous situations occur during the blowing process.
In summary, although fuse resistors have an action of melting to trip on overcurrent, they do not truly perform the same function as a fuse. It is incorrect to replace fuses with fuse resistors in most applications to reduce costs.
