What Is the Difference Between Fusible Resistors and Fuses?

Chargers and external power devices are often subject to in-rush current and sometimes experience voltage spikes. Both of these occurrences present a risk of damage to a circuit; therefore, most devices like them contain overcurrent protection components. Due to the greater demand for faster, more powerful charging in recent times, designers have had to put a strong emphasis on safety while being challenged by cost and size constraints, alongside more stringent efficiency requirements. To meet this demand, manufacturers may use traditional fuses which provide simple overcurrent protection, or they may choose to install fusible resistors. To learn why designers might consider the latter, read on as we compare these overcurrent protection devices.

In electronics, a fuse is an electrical safety device that provides overcurrent protection for a circuit. It is essentially a metal wire or strip that melts when too much current flows through it, thereby opening the circuit and stopping the flow of electrical current. Fuses are generally made of copper or silver and have a melting temperature typically between 962 and 1083 degrees Celsius, alongside a very high thermal coefficient of resistance. As a result, the temperature of a fuse will increase more quickly when an overcurrent condition occurs so that it reaches its melting point sooner.

As sacrificial parts which will break down after a single overcurrent event, fuses are often used as a backup which will interrupt a circuit to reduce the risk of fire or irreparable damage to the rest of the network. However, for the more frequent current spikes that occur when an electrical device is first turned on, fuses do not offer any protection. Therefore, fusible resistors are often used, as they combine the benefit of overcurrent protection and inrush current protection in a single component.

A fusible resistor opens up like a fuse when its current rating is exceeded; however, when the power isn’t exceeded, it serves as a resistor limiting current. In this way, the fusible resistor is able to limit current in-rush in normal conditions and operate like a fuse in the case of dangerous overcurrent conditions. The component is generally a nichrome element with a melting temperature of around 1400 degrees Celsius, meaning that it has a low thermal coefficient of resistance and will have a stable resistance over temperature. Consequently, fusible resistors are commonly used as the main overcurrent protection component in a power supply or charger.

By combining the functionality of two devices into one, the fusible resistor saves space. This being said, the heat generated by the fusible resistors could require spacing between components. Fusible resistors rated up to 10 W require other parts to be at least 0.5 inches away, while 1-inch spacing is needed for those rated above 10 W. Therefore, while they are often very useful in a number of assemblies, fusible resistors may not be suited for power supplies that need to be in small, compact packaging. Moreover, a fuse will be employed alongside a fusible resistor to prevent damage without melting by protecting surrounding components in case the fusible resistor reaches too high of a temperature.

In conclusion, whereas traditional fuses present an effective way of protecting from current spikes, fusible resistors may be used to combine overcurrent and in-rush current protection via a single device. As such, if you are in need of durable electronic parts for your assembly, rely on Aerospace Orbit, a premium parts procurement platform. Backed by speedy turnaround times and unmatched cost savings, we are ready to help customers meet their operational deadlines and strict requirements with ease. We invite you to peruse our inventory of more than 2 billion new, used, obsolete, and hard-to-find components to fulfill your product needs ASAP! Begin the purchasing process with us today to find out all that we can do to support you as your strategic sourcing partner for electronic parts.


March 17, 2022

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