Now if a person touches the faulty appliance, he gets an electric shock because the person comes in direct contact of the mains through the live wire. These are time delay fuses, which allow a little fluctuation in the amperage before blowing. This is the case despite the fact that most electrical fires […], Your email address will not be published. To prevent this from happening, �weak links� are deliberately placed in the circuit which break the flow of current before any real damage is done. Now, if the person touches the body of that appliance, he gets an electric shock. Specifically, to protect connected equipment, personnel and installations from excessive currents, whether from faulty wiring, improper use or operation of equipment or outside current surges. If the fuse is put in the neutral wire, then due to some defect in the appliance an excessive current flows in the circuit, the fuse blows off and current stops flowing in the circuit, but the appliance remains connected to the high potential point of the supply through the live wire. If you have an older home and you’re not comfortable with having an FPE fuse box, it’s completely understandable. to connect a bulb and a fan with the mains. This process is applicable only for alternating current since direct current cannot be raised. Fuses or Circuit Breakers: Which should you use? (a) What is the purpose of a switch in a circuit? Source: bbc.co.uk. The a.c. is supplied to our houses at 220 V of voltage and 50 Hz of frequency. Explain the meaning of the statement ‘the current rating of a fuse is 5 A’. When a high current flows through the electric circuits due to short circuit or overloading, the fuse wire heats up and melts. From this meter, connections are made to a main switch and to a main fuse in the distribution box. Our current limiting fuses meet the UL and NEC codes. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit. (c)A fuse is connected in ________ with the ________ wire. (a) Identify and write live (L), neutral (N) and earth (E) against the correct number. To do so: These fuses consist of a carrier that slots into the consumer unit and suspends a strand of fuse wire between two screwed terminals. The fuse breaks the circuit if a fault in an appliance causes too much current flow. The voltage of source gets divided connected in series in all the three bulbs and they operate at the same time. What is the use of a fuse in a household electric circuit? Most appliances are marked with their wattage and voltage, so you can calculate the amperage of the fuse you should add to the circuit as follows: Choose a fuse that is the nearest size above the calculated required amperage. (i) In the set A, all the three bulbs are in series connection. The electric power generated at the power generating station at 11 kV and 50 Hz respectively. Clearing I²t: The total I²t passed by a fuse as the fuse clears a fault, with t being equal to the time elapsed from the initiation of the fault to the instant the fault has been cleared. (d) The glow of bulbs B and C will not be affected if bulb A gets fused. Therefore 20 A wire will be more thicker than the 5 A wire. If a person touches the faulty appliance in this situation, he gets an electric shock because the person will come in contact with the mains through the live wire. How does a fuse protect an electric circuit? Replace the fuse by pressing a new one of the correct rating into the spring clips, and refit the carrier into the consumer unit. (b) Why is the switch put in the live wire? Before connecting the cable from pole to the meter in a house, first a fuse of high rating is connected in the live wire at the pole or just before the meter. It is necessary to have an earth wire installed in a power circuit because the power circuit carries high power and costly devices. The current rating of pole fuse is ≈ 50 A. Hence, the fuse must be connected in the live wire only. The colour coding of wires in the circuit of house wiring helps us to connect the switch, fuse, sockets, etc. With the way that technology is constantly improving, it’s important to have an up to date communication system. There’s an internal mechanism that “trips” with an unsafe electric surge tries to flow. State the function of each of the following in a house circuiting: (a) kWh meter, (b) the main fuse, and (c) the main switch. Explain the reason. Type T screw in like S fuses. Tri-National Standards specify fuse performance and maximum allowable fuse Ip and I²t let-thru values. (i)The current rating of the fuse wire is directly proportional to the thickness of the fuse wire. Performance & security by Cloudflare, Please complete the security check to access. Federal Pacific Electric (FPE) was the leading manufacturer of these panels until the dangers of aluminum wiring got discovered. But it’s how the cut the flow that’s the difference. (c) A fuse is connected in series with the live wire. The other downside is that the switch can flip due to vibration and movement, which can lead to major frustration. Since porcelain is an insulator of electricity, hence the fuse wire is stretched between the two metallic terminals T1 and T2 in a porcelain holder. What is its value in S.I. Give two reasons why a fuse must not be replaced by an ordinary copper wire. (b) What is the nature of the current transmitted from the power station? Your email address will not be published. The main fuse is connected in series only in the live wire before the main switch in the distribution board of a house circuit. The most common fuse arrangement is shown in the above figure. Higher the thickness of fuse wire, higher will be the current rating. Electric fuse is required in all electrical appliances to prevent damage from excessive current flow and during short circuit. How is a fuse put in an electric circuit? Thus it is highly unsafe to use a fuse in the neutral wire. This electrical part is a small length thin wire created using lead and tin alloy. It is easy to see if a MCB has tripped, as its switch will be in the �off� position. The answers are accurate pertaining to the concepts mentioned in this chapter. Cut off any excess wire and refit the carrier into the consumer unit. The voltage of power generated at the generating stations is first stepped up before its transmission. State one characteristic of the material used for fuse. ‘A fuse is rated 8 A’. How should the several electric lamps be connected with the mains so that the switching on or off a lamp has no effect on the operation of other lamps? There are many other ways, like circuit breakers or protective relays, and here are 10 reasons why you might just want to consider fusing instead. If the current in a circuit exceeds the current rating of the fuse wire it melts. Therefore, it is deceptive and dangerous to connect a switch in the neutral wire. Copper has very low resistivity and high melting point. But, they’re still out there. The main switch is a double pole switch and has an iron covering. (c) To which wire joined to 2 or 3, is the fuse connected? A switch is an on-off device for current in a circuit (or in an appliance). Therefore if due to some fault, the fuse of one appliance burns, it does not affect the operation of the other appliances while in a tree system when fuse in one distribution line blows, it disconnects all the appliances connected to that distribution circuit.
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