Fusible resistor is a special type of resistor made for the purpose of protection of any circuit . This resistor made by such material that have characteristic of fusing without flames or without excess heat generation when current load jumps suddenly more than required. When you see normally in any circuit this looks roughen and some Bigger in size and Not have Smoothness and Shining as normal resistor . This resistor always connected in series with input main power supply to circuit.
Fusible resistor are useful for highly sensitive circuits of lower power requirements and applications where the overload and surge handling requirements are not too severe. When any components of that circuit get faulty and change their behaviour out of design property , than it may be there a fluctuation of current load change and like short circuit condition (not fully shorted) occur. In this situation other components of circuit can get damaged easily or even excess heat and flames destroy whole system of device. Fusible resistor provides guarantee of safety of whole circuitry by Fuse itself quickly .
Generally any fusible resistor manufacterd of between very less value like 10Ω to 100Ω and these value used accordingly to required circuit. Wirewound type fusible resistors are mostly used.
Fusible resistor acts like a safety fuse, but there are difference between Fuse and fusible resistor.
A normal glass tube fuse used where high surge current load devices used like 2A, 8A, 10A etc and this will burn when high load occur according to fuse capacity or when short connection .
Fusible resistor used in circuit which operates high voltage with small or lower current such as 100ma, 250ma. A fusible resistor can pass the pulse of high volt like 500v without failure, but it must fuse quickly without flames when 100v short circuit overloads.
Note - If any Fuse resistor Fused in any circuit – It denotes there are any fault in any component . If you get shorted the fuse resistor through wire then the highly risk of damage other components
So Firstly check other components of that circuit carefully and change before changing or shorted the fuse resistor. Because if any components not get fully damaged but some their property changed then also Fuse resistor will fused again and again.