ICSE Class 8 Answered

Overloading occurs when too many appliances are connected to a single socket. If the fuse is not used to protect the circuit then overloading can causes heating of household wiring to a high temperature and may also catch fire. While the short circuiting occurs when the live wire and neutral wire come in contact with each other. As the two wires come in contact the resistance in the circuit becomes very low and the current flowing through the wire become very large and wire may catch fire due to the rise in the temperature of wiring. The causes of voltage fluctuation is poor supply of electricity through transmission line, interference in the transmission or wiring issues (too many devices are used simultaneously). 

If the fuse is connected in the circuit then the fuse wire melts and breaks the circuit when the current exceeds a safe value.