Tag: electric fuse

Heat lost per second per unit surface area of fuse wire is
$H = \dfrac{I^2 \rho }{2 \pi ^2 r^3}$

Answer: B
a fuse wire is a type of high resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit. resistivity is directly depend on resistance for a particular conductor , hence high resistance means high resistivity which is called specific resistance.

Fuses are safety devices that are to be built into our electrical system. If there were no fuses and we operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, fuses are designed to trip or blow, stopping the flow of current to the overloaded cable.
Fuse is a piece of wire of a material with a very low melting point. When a high current flows through the circuit due to overloading or short circuit, the wires gets heated and melts. As a result, the circuit is broken and current stops flowing. 
The fuse must always be connected to the mains and it must be of correct current rating. For example, a 15-ampere fuse should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps.
Hence, the statement 'the current rating of a fuse is 5 A' means that the fuse should trip when the current through it exceeds 5 amperes. So correct option is B.

In our homes, we receive supply of electric power through a main supply (mains), either supported through overhead electric poles or by underground cables.The live wire and neutral wire, coming from the electric pole, enter a box fitted just outside our house which has a main fuse. The fuse is connected in series with the live wire. This is done so because it is only the live wire which has a high potential of 220 volts unlike the neutral wire which carries zero potential. The fuse has a high rating of about 50 amperes. Thus it prevents any damage such as fire to the entire electrical wiring entering the house due to short-circuit or overloading.
The two wires then enter the electricity meter which records the electrical power consumed by us in kilowatt-hour (kWh).
Hence, A fuse is connected in series with the live wire.

A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing. The fuse is arranged in series to carry all the current passing through the protected circuit. The resistance of the element generates heat due to the current flow. The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit.
The fuse element is made of zinc, copper, silver, aluminum, or alloys of tin and lead to provide stable and predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt quickly on a small excess. The element must not be damaged by minor harmless surges of current, and must not oxidize or change its behavior after possibly years of service.

The live wires coming out from the output terminals of kWh meter has another fuse in it called the main fuse. 
The fuse is connected in series with the live wire before it enters the household circuit. This is done so because it is only the live wire which has a high potential of 220 volts unlike the neutral wire which carries zero potential. The fuse has a high rating of about 50 amperes. Thus it prevents any damage such as fire to the entire electrical wiring entering the house due to short-circuit or overloading.Hence correct option is A.

The live wires coming out from the output terminals of kWh meter has another fuse in it called the main fuse. 
The fuse is connected in series with the live wire before it enters the household circuit. This is done so because it is only the live wire which has a high potential of 220 volts unlike the neutral wire which carries zero potential. The fuse has a high rating of about 50 amperes. Thus it prevents any damage such as fire to the entire electrical wiring entering the house due to short-circuit or overloading.Hence correct option is A.

The fuse consists of a porcelain base on which two metal contacts are fixed. The incoming and outgoing phase wires are connected to these metal contacts. Porcelain made fuse carrier used for holding the fuse element or fuse wire. This porcelain made fuse carrier is inserted to the porcelain base for connecting a load side circuit to source side circuit. The main advantage of this type of fuse is that, the fuse carrier can be removed from the fuse base without any chance of coming in contact with the live part of the circuit.

Fuse wire are used in electric circuits to protect home appliances from damaging by huge amount amount of current. Fuse wire should be such that it melts immediately when strong current flows through the circuit. The same is possible if its melting point is low and resistivity or the resistance is high.

The rating of fuse is ,if the current is greater than the rated current then the fuse blows.
So if the rating is 10A, then it is the maximum current that passes through fuse.
If two such fuses are connected in parallel , the total current divides into two components where each can be maximum of 10 A. The maximum total current can be 20 A.
If they are connected in series,same current flows through each of them. The maximum current allowed would be the minimum rated current among the two fuses.So here the current rating will be 10A.