Safety Devices Electrical Fuse Fuse 1 1 Introduction

Safety Devices: Electrical Fuse

Fuse 1. 1 Introduction of Safety Devices Now a day’s electricity has become impossible to imagine our life without electricity. It is one of the best gifts of science to humankind. It may be any industry, school, college or our house we use electricity everywhere. As we read in newspaper sometimes electricity can cause accidents which damage our property or it may even take human life. So we need some safety devices to protect us from electricity related accident like fire or electrocution.

Fuse Some of the important safety devices are • Fuse • MCB(Miniature Circuit Breaker) • Ground fault circuit interrupt

1. 2 Electrical Fuse

* A fuse is a short piece of metal, inserted in series with the circuit which melts and breaks the circuit when excessive current flows through it, thus it protects the circuit. * The basic purpose of the fuse is to provide protection from very high current. * Simplest and Cheapest form of protection and is used for protecting low voltage equipment's against overloads and short circuits. * It is made up of a thin tin plate copper wire, so that it has low melting point, hence making it easier to break the circuit. Fuse

Fuse Each fuse has a “rating”. The hi thicker the wire used in the fuse (as this lowers resistance offered by the fuse, to generate less heat). Fuse works on the basis of heating effect of electric current, as it melts and breaks the circuit, protecting the devices connected to it for future use. It has inverse Time-Current characteristics.

Fuse Symbol: There are three symbols of fuse

Fuse Application of fuse: Near main switch board, extension box, UPS, Fridge, Voltage Stabilizer, In transmission network, In industry near main electrical panel, etc.

Fuse 1. 3 Working Principle: A fuse is inserted in series with the circuit which is to be protected. Melting point of a fuse material is low as it does allow the normal rated current to flow through it without overheating or melting. when the current exceeds beyond its rated value, the fuse element gets overheating and it starts melting, thus finally it breaks(opens) the circuit which is to be protected.

Fuse What can be the reason for high Current? • Short-Circuit • Overloading • Problem from network • Thundering and lightening Transmission

Fuse Example of Short-circuit: Example of overloading

Fuse Short Circuit: The term short circuit is most commonly used by electricians to refer to the situation in which a hot wire carrying live current touches a neutral wire. Overloading: The current in a circuit depends on the rating of the appliances connected to it. If the total power rating of the appliances exceeds this permitted limit of wire to switch board, they tend to draw a large current. This is known as overloading.

Fuse 1. 4 Component of fuse: The main components of a standard fuse unit consist of the following items: • Metal fuse element • Set of contacts • Support body

1. 6 Types of fuse: Fuse

Fuse The major two categories of fuses include: • Low Voltage Fuses • High Voltage Fuses

Fuse 1. 6. 1 Low Voltage Fuses In order to understand Low voltage fuses better; we can further classify it further into: • Semi Enclosed Rewireable Type • Totally enclosed or Cartridge Type

Semi Enclosed Rewireable Fuse: * It is also known as KIT-KAT type fuse. *It is used where low value of fault current are to be interrupted so mostly used in the case of domestic wiring and small scale usage. *It has two parts: 1)a base (to hold fuse carrier) 2)a fuse carrier Fuse

* both base and fuse carrier are made up of porcelain, base is fixed while fuse carrier ( which carries the fuse element) is moving, fuse carrier is taken out when the fuse blows out and after replacing it with the new fuse wire , it is again placed over base. * Semi enclosed rewireable fuse are made upto 500 A rated current but their breaking capacity is low, So they are used only for domestic or small loads. *main advantage is that it is easy to replace blown fuse or blown wire without extra cost. Usage: near main meter connection, on switch board, at different places in house iring. Fuse

High Rupture Capacity (H. R. C) Cartridge Fuse: Fuse

ADVANTAGES • They are capable of clearing high and low fault currents. • No deterioration with age • No maintenance required • Reliable discrimination Fuse

Fuse 1. 10 Possible Accidents without a fuse: If fuses are not installed in the circuit, then there is no safety barrier to stop excessive current to flow in the circuit due to short circuit/overloading/etc. which can not only lead to wrecking the devices connected to the circuit, but also serious fires due to heating.

1. 11 Applications of Fuses: • Power Transformers • Home Electrical Wiring • All Electrical Appliances (Air Conditioners, Washing Machines, TV, Music Systems, etc. ) • Motor Starters • Mobile Phones • Laptops • Power Adapters • Cameras • Printers, Scanners and Photocopiers • All Automobile (Cars, Bikes, Trucks, Buses, etc. ) • All Electronic Devices (Hard Disks, DVD Writers, DVD Players, etc. ) • Gaming Consoles Fuse

Fuse Prepared by M. S. Anwar TGT (WE)