Safety Device – Fuse

CONTENT

• Fuse
• Types of Fuse
• Detecting Fault in a Circuit

FUSE

Fuse is a protective device, designed to melt at the passage of excess electric current through it. It can also be defined as a device for opening circuit, by means of a conductor designed to melt when an excessive current flows along it. The conductor actually designed to melt is called fuse element.

Fuse element is the part of the fuse that is designed to melt and then open the cct

Current rating of a fuse: it is the minimum current which the fuse will carry for an indefinite/ unlimited period without deterioration of the fuse element

Fusing current: is the minimum current that will cause the fuse element to heat up and melt/ rapture or blow.

Fusing factor is the ratio of the fusing current upon the current rating.

Fusing factor = fusing current/ current rating

EVALUATION

1. Define the following terms (a) fuse (b) fuse element (c) current rating of a fuse
2. State the relationship between fusing factor, fusing rating and current rating

TYPES OF FUSE

• Re-wire able fuse
• Cartridge fuse
• High breaker capacity fuse
• Others

DETECTING FAULT IN ELECTRIC CIRCUIT

• Merger tester – insulation resistance test
• Test bell – polarity test
• Earth-loop impudence tester – test for earthling
• Continuity tester – test for continuity

EVALUATION

1. List three types of fuse
2. Mention four ways of detecting fault in an electric circuit

READING ASSIGNMENT

Read more on safety devices – New school physics (pg 83-84)

GENERAL EVALUATION

1. Define the term scalar and vector quantities. Give two examples each
   1. A rectangular box of dimension 6cm x 10cm x 2cm weighs 15N. Calculate the density of the density of the box.

WEEKEND ASSIGNMENT

1. Fuse is a protective device, design to ……….. (a) stick (b) melt (c) disappear (d) repel
2. The conductor designed to melt is called ……. (a) fuse element (b) fuse (c) resistor (d) cartridge fuse
3. The following are examples of fuse except ……. fuse (a) re-wire able (b) merger (c) cartridge (d) high breaking capacity
4. Which of the following correctly gives the relationship between linear speed v & angular velocity w of a body moving uniformly (a) v=w r (b) v=w²r (c) v=wr² (d) v=w/r
5. The motion of the prongs of a sounding turning fork is (a) random  (b) translational (c) rotational  (d) vibratory

THEORY

1. Define the following terms (a) fuse (b) fuse element (c) current rating of a fuse
2. Mention four ways of detecting fault in an electric circuit.