Ano ang pinakamaliit na kontinente sa mundo? State one characteristic of material used for the fuse. (b)The heating element of geyser should be connected to live wire and neutral wire. Draw a labelled diagram of a three pin socket. At what the bulb A connected with the mains? The Recommended Practice is available for download at www.easa.com. Which of the cables, one rated 5 A and the other 15 A will be of thicker wire? Local earthing is made near kWh meter. (a) Name the switch/switches to be closed so as to light all the three lamps. When a fuse is in an electronic circuit and the current exceeds the rated level, the fuse melts (blows), thus breaking the circuit and preventing the excessive current from flowing. How is a fuse put in an electric circuit? (b) A fuse wire is made of an alloy of lead and tin. Fuses are an essential component of any electrical system that uses line voltage and has the possibility of short-circuiting or overheating and causing a fire. The earth pin is made long so that the earth connection is made first. For earthing an electrical appliance, one has to remove the paint from the metal body of the appliance where the electrical contact is made. (a)Identify and write live (L), neutral (N) and earth (E) against the correct number. Verify your number to create your account, Sign up with different email address/mobile number, NEWSLETTER : Get latest updates in your inbox, Need assistance? (ii) In ring system the sockets and plugs of same size can be used while in a tree system sockets and plugs are of different size. What do you mean by the term local earthing? Such parts can be installed in and subjected to normal or non-normal atmospheric conditions. The (a) The three connecting wires used in a household circuit are: (b) Among them neutral and earth wires are at the same potential.

The diagram in Fig. Installing and Removing Fuses

The earth pin is thicker so that even by mistake it cannot be inserted into the hole for the live or neutral connection of the socket. State two circumstances when one may get an electric shock from an electrical gadget. Colour When one of the bulbs in set A is fused, the other three bulbs also cease to glow. Seals should be inspected to ensure that moisture has not entered the interrupting chamber. The metal ends are the two terminals of the fuse.

But when the current exceeds the rated maximum, the conductor melts, and the circuit is broken. (d)To which wire should the switch and fuse be connected? A fuse is an overcurrent responsive safety device used to protect an electrical circuit from the effects of excessive current. Identify and write live (L), neutral (N) and earth (E) against the correct number. NFPA 70B - Chapter 18. Fuse is called as the "First Line of Defense" so it should be placed right after the power cord is connected to the circuit board. The metal case should be connected to earth wire. If you want the fuse to be accessible from outside the project’s enclosure, you should choose a panel-mount holder instead. wiring. (ii) The switch of the appliance is the red coloured,

Similarly if the bulb is in on position as shown in Fig. Why are switches and fuses always placed on the hot side of the circuit rather than on the neutral wire of the circuit? Give reason. All rights reserved. How is the bulb A connected with the mains? All Rights Reserved. suffer a fatal electric shock. A power circuit uses a cable using three different wires. not depend on its length. (a) The three wires are: Live wire, Earth wire and Neutral wire. If the fuse is in the neutral wire, then although the fuse burns due to the flow of heavy current, but the appliance remains at the supply voltage so that on touching the appliance current flows through the appliance to the person touching it. 11kV to 132kV using the step-up transformer.

the live wire of a very high potential. Fuses can be current-limiting or non-current limiting, sand or liquid filled, or vented expulsion type. At what voltage and frequency is the electric power generated at the power generating station? So, bulb B will glow at 110V.

Explanation: A switch must be connected in live wire, so that when it is in 'off' position, the circuit is incomplete and no current reaches the appliance through the live wire. • Excessive erosion of the inside of the fuse tube should be checked for discharge tracking and dirt on the outside of the fuse tube, • Improper assembly that might prevent proper operation should also be checked. What is the nature of current transmitted from the power station? At what voltage is the electric power from the generating station transmitted? case of excessive current, it is dangerous to connect the switch in the At what voltage and frequency is the a.c. supplied to our houses? alternating current. The figure above shows the most common fuse arrangement in which the fuse wire is stretched between the two metallic terminals T. Is directly proportional to the thickness The standard describes industry best practices for the repair, rewinding, and testing of electrical apparatus to maintain or enhance the reliability and energy efficiency of both AC and DC motors and generators. Chapter 2: Magnetic Effects of Electric Current. This ensures the safety of the user because if the appliance is defective, the fuse will blow off. (a) A fuse is a short piece of wire of high resistance and of material low melting point. But the appliance remains connected to the high potential terminal through the live wire. What is its value in S.I. Explain with the aid of a simple diagram, the transmission of electric power from the generating station to your house. At the intermediate sub-station, the voltage is stepped down to 11 kV using a step-down transformer and is transmitted to the city sub-station, where the voltage is further stepped down to 220 V and is supplied to our houses. The main fuse in a house circuit is connected on the distribution board, in live wire before the main switch. How are the lamps connected: in series or in parallel? (i) In a ring system the wiring is cheaper than tree system. Thus, when the fuse of one bulb blows off, the circuit gets broken and current does not flow through the other bulbs also. © 2020 Endeavor Business Media, LLC. The fuse should always be disconnected, if possible, and de-energized from electrical power sources before servicing, and an electrically safe work condition per NFPA 70E, Standard for Electrical Safety in the Workplace – Article 120 should then be established. Note: Power fuses of the vented type are not to be used indoors, underground, or in metal enclosures unless identified for such use by the manufacturer. Actually the fuse should be placed after the switch by code. So, such fuse cannot be used. That give the reason? If the switch S1 is operated, the connection 'ab' is changed to 'bc', which completes the circuit and the bulb lights up [Fig. (c) What precaution do you take while handling a switch? When did organ music become associated with baseball? What purpose is served by the terminals of a three way pin plug? Let a switch S1 be fitted at the bottom and a switch S2 at the top of the staircase. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply. What is the pole fuse? This is not always the case with the neutral. wire. The fuse wire is fitted in a porcelain casing because porcelain is an insulator of electricity. (b)To which of the two wires should the heating element of an electric geyser be connected? NFPA 70B - 18.2.2. In Part 1 of this two-part series we focused on fuses rated 600V or less. A fuse is always connected to the live wire of the circuit. Want a call from us give your mobile number below, For any content/service related issues please contact on this number. James Stallcup Sr. and James Stallcup Jr. The plate is surrounded by a mixture of charcoal and salt to make a good earth connection. The figure above shows the most common fuse arrangement in which the fuse wire is stretched between the two metallic terminals T1 and T2 in a porcelain holder. NFPA 70B - 18.2.3.1.

The safe limit of current which can flow through the electrical appliance is I = P/V = 5000/200 = 25 A; which is greater than 8 A. The maintenance procedure should stress the environmental or operating conditions of a particular installation. Now if a person touches the appliance, he may get a shock as the person will come in contact with the live wire through the appliance. Therefore 15 A current rated wire will be thicker. An alloy of lead and tin is used as a material of fuse because it has low melting point and high resistivity. The insulators should be cleaned, particularly where abnormal conditions such as salt deposits, cement related type dust, or acid fumes are present in dangerous amounts, such intervals of maintenance will help prevent flashover conditions.

Name the colour code of the wire which is connected to To which wire is the metallic case of an electric appliance connected? Fuses should always be connected to the hot wire and should be placed before any other component in the circuit. The 20 A fuse wire will be thicker so that its resistance be low.