Page 102 - Electrician - TT (Volume 1)
P. 102

ELECTRICIAN - CITS




           Fuses
           A fuse is a safety device connected in series to the circuit which protect the electrical apparatus from possible
           damage when abnormal current flows through it. When normal current flows , the serves as a conductor but when
           the current flows above the predetermined value through a circuit due to short circuit , heat s produced to melt the
           fuse wire thus breaking the circuit to protect equipment from damage due to excessive value .
           Classification of fuses

           Fuses may be classified into two groups
           1  Those designed to protect the circuit from short circuit only
           2  Those designed to protect over load and short
           Parts of fuse



















           1   Fuse wire  2    Fuse carrier  3     Fuse carrier contact   4   Fuse base    5    Fixed contact
           Fuse wire
           Fuse wire are bare wires made of easily melting material having high specific resistance usually standard alloy
           63%tin and 37% lead it is used low current say up to 5 A and tinned copper for large value of current .
           Fuse carrier
           The part to which the fuse wire is fitted is called fuse carrier and is made of porcelain.
           Fuse carrier contact
           These are the contact strip which engage or disengage the fixed contacts of the fuse base and have a fuse wire
           attached to them.
            Fuse base
           It is the fixed part of the fuse and is made of porcelain .
           Fixed contact

           These contact are provided in the porcelain base of the fuse and engage with the fuse carrier contacts
           Minimum fusing current
           Minimum fusing current is the least value of current at which the fuse wire is melt .
           Current rating of fuse element

           Fuse element current which it can carry without melting . It is the value is always less than the minimum value of
           fuse current.
           Fusing factor
           The ratio of minimum fusing current and rating current of the fuse element is called fusing factor. Fusing factor
           always greater than unity
           Types of fuses
           Two types of fuses are used




                                                           89

 CITS : Power - Electrician & Wireman - Lesson 20-25  CITS : Power - Electrician & Wireman - Lesson 20-25
   97   98   99   100   101   102   103   104   105   106   107