Page 266 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

is opened. The circuit cannot be closed again till the base plate of the iron cools down again. After cooling the
iron, the bimetal strip regains its original normal position and thus the circuit is again completed. By means of
an insulated knob on the contact point, the distance between the contact points is adjusted. This regulates the
temperature of iron for different types of clothes. It should always be kept in mind that the setting of the bimetal
strip should not Tie disturbed because the rate of linear expansion is known to the manufacturer only. If once its
setting is disturbed, it will stop functioning properly.
A condenser is connected across the contact point of the bimetal strip. Its function is to minimize the sparking at
the contact point and thus increase the life of the contact point. A short-circuited condenser decreases the life of
the element because it will always give path to the current, and the iron even afterithas become hot cannot then
be operated through the contact point.
An indicator lamp of 2.8 V is also fitted in the handle of the iron and is connected across a small resistance which
is connected in series with the element. When the lamp lights up, it indicates that current is passing through the
heating element and when it goes off, it shows that iron has attained the required temperature and the current has
stopped flowing. Automatic irons are of 750 W only.

7 Hot Plate
Hot plates are used for cooking food stuffs. These are of two types, namely, the single hot plate and double hot
plate

Double hot plate Single hot plate
The heating element of the hot plate consists of a single or double spirally wound heating element which is
embedded in between an insulating cemented material like plaster of paris or fire clay and then baked hard. The
fire clay is then covered with a steel plate and the foodstuff boils over this plate. In simple design, the heating
element is divided into two parts of equal heating capacity, as shown in Fig. Each element is independently
controlled by a separate switch. When either switch is in the ON position it gives half of the full heat and when
both switches are ON the full heat is available.

In other cases, heat is controlled by a separate special rotary switch which has four positions, giving full heat,
medium heat, low heat and OFF. The heating element is divided into two parts. When the switch is in the full
position, the two elements are connected in parallel and the element takes its full rated current.
8 Water heater
Water heaters are of two types:
1 Immersion water heater

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CITS : Power - Electrician & Wireman - Lesson 101-103