Exam Question
(a) Explain three methods of overcurrent protection for electrical circuit. (8)
(b) Explain with aid of diagram, the meaning of the term inverse current-time characteristic. (8)
ETO
ETO Exam papers
📅 Aug 2025
Reference Answer
(a)
(i) Fuse:
an electric fuse is based on the principle of heating effect of electric current. It is made of thin metallic wire of non-combustible material. When an excessive current flows in the circuit, it generates heat in the circuit which leads to melt the fuse due to its low melting point, and it also opens the circuit. Fuses are employed usually as backup protection against short circuits of equipments and for cable protection.
(ii) Thermal overload relay:
(i) Fuse:
an electric fuse is based on the principle of heating effect of electric current. It is made of thin metallic wire of non-combustible material. When an excessive current flows in the circuit, it generates heat in the circuit which leads to melt the fuse due to its low melting point, and it also opens the circuit. Fuses are employed usually as backup protection against short circuits of equipments and for cable protection.
(ii) Thermal overload relay:
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