• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Current rating of fuses and MCB's.

Extracts from this document...

Introduction

CURRENT RATING OF FUSES AND MCBS

Name of Instructor: Miss. B.S.K. Subasinghe                        

Name                :         Perera K.N.S.

Index No        :                  020287        

Field                :                 ENTC

Date of Per.        :            10/12/2003

Date of Sub.:           19/12/2003    

CALCULATIONS:

For the fuse  image00.png

For MCB image01.png

From graphs drawn,

Fusing current for 5A fuse        =        

image02.png

Tripping current for 2A MCB        =        

image03.png

RESULTS

Fusing Factor

Tripping Factor

DISCUSSION:

Fuses and Miniature Circuit Breakers (MCBs) are used to protect electrical equipment and for the safety of the users. The conditions that require circuit protection are direct shorts, excessive current and excessive heat. When one or more

...read more.

Middle

Re-wirable fuses

These have a thin wire that is held on a ceramic holder. The wire is designed to burn when a high current passes. An advantage is the reusability but it is vulnerable to mishandling where incorrect fusing elements can be fitted by inexperienced people, putting users in danger. Other Problems with this type are the oxidization (causes the cross section of the wire to reduce reducing the current carrying capacity) and longer fusing time.

Cartridge fuses

Fuse wire is enclosed in an inert environment. Once burnt, the fuse has to be replaced i.e. a repetitive cost when replacing.

High Rupture Capacity (HRC) fuses

These are used for high current protection. These have a ceramic outer barrel. The fuse wire is covered with sand in order to quench the arc produced when the fuse burns. The ceramic barrel can withstand the shock of the interruption of the high current.

Usually semi-enclosed rewireable fuses have about 1.7-2 times the rated current carrying capacity. In this practical the fusing factor was       . This value is rather high. However the value might not be the exact fusing factor of the fuse used due to the errors that are present in the practical.

MCBS

Circuit symbol:

...read more.

Conclusion

  • Rewireable fuses tend to weaken with time due to oxidization. So the fuse will not be able to withstand the rated current.

Other Protection Techniques

  1. Large Current Protection - Here simply breaking the circuit is not enough to stop the flow of current. The current in some circuits is strong enough to jump, or arc, across the gap in the circuit, even after the circuit breaker has been tripped. Circuit breakers that deal with high levels of current, especially direct current, have methods of getting rid of the energy in the arc and stopping the current.
  • In oil breakers, the design of the circuit breaker forces the arc of broken circuit through a sealed container of oil or gas. The arc heats the oil around it. The hot oil begins to circulate in the tank, carrying heat and energy away from the arc.
  • Air-blast circuit breakers send the arc through compressed air, which is immediately released to the outside, carrying the heat and energy of the arc with it.
  1. Fuses used in vehicles and motors - Some of these fuses are Ribbon type, Knife blade cartridge type, Plug type with ribbon tube, Copper fuse link, Fibre tube, Cartridge type with glass tube and wire fuse link.
  1. Sensitive Equipment - Fuses used in 13A plug tops as well as in some sensitive equipment for additional protection (voltage stabilizers, computer power supplies) – These are mostly cartridge type fuses.

REFERENCES

Electrical Engineering Handout

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. Characteristics of Ohmic and Non Ohmic Conductors.

    The semi conductors such as silicon or germanium are also non ohmic conductors. The semi conductors are again divided such as intrinsic and extrinsic. The graphs that are obtained from the various non ohmic conductors are as follows. Light Dependant Resistor B I+ A V- V+ I- This shows that the listed components are not ohmic conductors.

  2. resistivity if a nichrome wire

    To overcome this problem the rust can be cleaned with sandpaper, or even replaced by new ones. Thickness of wire This may differ on the wire, as the wire may not be uniformly thick. This causes a change in the cross sectional area of the wire.

  1. Characteristics of Ohmic and non-Ohmic Conductors.

    In this experiment, I will be noting the Current for the various Voltages at intervals of 0.2 V, in the same manner as I did for the previous experiment, in descending order, and then in ascending order. The average of he two will then be taken, to obtain reliable results.

  2. The strength of an electromagnet.

    the current would double the strength of the electromagnet is not correct. If you double the current the strength increases by only ??? There is one anomalous result, at current 1.3 amps in experiment 2. The result is less than I would expect.

  1. investigating the relationship between the diameter and the current in a wire at its ...

    Determining a material to use for the test wire I decided to use Tin plated Copper wire. This is because it has the greatest amount of different diameters available. Other available wires included Aluminium and Constantine. There was only 1 diameter of aluminium available and 5 diameters of Constantine.

  2. Investigating the factors affecting the size of current flowing through a length of resistivity ...

    true value of the current which is what I predicted earlier in the investigation. If you look at the graphs again, you will see that the values my experiments produced have a higher current value than the predicted values. This means that in my experiment more current was flowing than I had predicted.

  1. How does the mass of copper plated in the electrolysis of copper sulphate solution ...

    the emersion of the electrodes at the same height, the height is going to be 8 cm. This is important because this depends on how much of the area of the electrodes are actually in the electrolyte being part of the electrolysis (being in the reaction).

  2. Geothermal energy is not easily accessible with our current technology. Our main focus was ...

    Radioactive heat is a result of radioactive decay. Sub-atomic particles are released during radioactive decay and these particles collide with other atomic particles. When they collide, the kinetic energy is converted into heat. A possible source of radioactive is heat is the usage of nuclear explosive devices.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work