Page 241 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

5 Fuses
It is a protective device which is connected is series with the live wire to protect the circuit from short circuit and
earth fault.
6 Contactors (Fig 11)
A contactor is an electrically controlled double break switch used for switching ON / switching OFF the electrical
circuit, similar to a relay with higher current ratings. It is controlled by a circuit which has a much lower power
level than the switched circuit.
7 Electro mechanical relays (Fig 12)
Electromechanical relays are electrically operated switches used to control a high powered circuit accessories
using low power signal. When an electric current passes through its coil it produces a magnetic field that activates
the armature to make or break a connection.
Current passes through its coil it produces a magnetic field that activates the armature to make or break a
connection.

Fig 11 Fig 12

8 Thermal overload relays (Fig 13)
It is a thermally operated electromechanical device that protects motors from over heating and loading.
9 Time delay relay (timers) (Fig 14)

Time delay relays are simply the control relays in - built with a time delay mechanism to control the circuit based
an time delay.
In time delay relays its contact will open or close after the pre-determined time delay either on energising or on
de-energising its no volt coil. It can be classified into two types as ON delay timer and OFF delay timer.

Fig 13 Fig 14

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CITS : Power - Electrician & Wireman - Lesson 93-100 CITS : Power - Electrician & Wireman - Lesson 93-100