One Lamp point
Two wires are connected to each lamp and switch. Live or
phase wire is always connected to the holder through the switch. The other wire
connected to the holder is always neutral wire.
When the switch is made on, both the phase and neutral wire
are connected to the holder and the lamp which is fitted in the holder starts
giving light. If any one of these wires is disconnected from the holder, the
lamp will not glow.
Lamp construction and
how it gives light
Ordinary lamp is known as incandescent lamp. This lamp
consists of that glass bulb which is evacuated or it contains some insert gas
inside it. The filament is made of pure tungsten wire which has got very high
resistance.
When the current is passed through this filament, it gets
heated and starts giving light. The lamp works approximately at 20000C.
Low wattage lamps (25 watts) are evacuated while higher wattage lamps have some
insert gas filled in them.
1. Lamp does not give light
Fuse may be blown off when other lamps do not give light, it
may be understood that the fuse is blown off. In such a case, the main switch
is made off and the fuse grip is taken out.
If the fuse wire is either broken or burnt out, this burnt
out or broken fuse wire is removed from its terminals and a new fuse wire of
the same length and size is connected to the terminals.
After connecting new fuse wire, the fuse is again blown off,
then it should be understood that there is short circuit. This short circuit
may be due to short circuit in the electric press, electric heater and electric
fan, etc. All the electric appliances should be disconnected and then the fuse
is again replaced.
If the fuse still
blows off then it indicates that there is a short circuit in the wiring. This
short circuit in the wiring may be in the wires passing from one room to the
other room through the pipe in the wall or it may be at a point where both the
wires are connected at a point.
2. Lamp may be fused
If all other lamps are giving light and only that lamp is not
giving light, then this lamp may be fused. Lamp should be removed and its
broken filament is looked for.
Sometimes, the broken filament is joined by shaking the lamp
to complete the circuit and the lamp used. By doing so, sometimes the wattage
of the lamp increases and such a lamp does not give light for more periods. It
is better to replace the lamp.
At the time of removing the lamp from the holder stand on
some stool, etc., this reduces the danger of shock. Sometimes it is seen that
the live wire touches the holder and the holder gives shock when it is touched.
If the holder is made of backlite, one can work as it is.
3. Switch may be Defective
When the lamp and the fuse are in order, then open the switch
cover with the help of connector screw driver by standing on a wooden stool
taking care that none of your body part touches the wall or ground. If there is
face plate then the face plate must be opened first by opening switch ring
fitted in the face plate.
Method of opening the
switch
These days’ fancy switch and plugs are fitted in the houses.
Open the face plate. Then internal portion of the switch and the switch
terminals will be visible. Now short circuit the two terminals with the help of
screw metallic blade.
While short circuiting the metallic portion of the screw
driver should not be touched.
If the lamp starts giving light by short circuiting, then
adjust switch contacts with screw driver.
If the lamp does not give light even by short circuiting,
then the supply should be tested at the switch terminal. Take a test lamp
connect one end of the test lamp to one terminal of the switch and the other
end of the test lamp to earth. i.e., in the bigger hole of the 3 pin plug which
is meant for earth?
If the lamp gives light, it means that the supply is there,
otherwise not. If the supply is there, then the lamp should give light by short
circuiting the terminals of the switch. If not, then the defect is in the
holder.
Defect may be in the
holder
When the switch is in order and supply is also available at
the switch, then the defect should be traced in the holder. For this, switch
off the supply. Sometimes the lamp does not give light if the holder is
“crossed”. This “cross” mostly occurs in brass holders. In crossed holder the
lamp terminals do not make contact with holder terminals (pins) and the lamp
does not give light.
To remove the “cross” in the holder open the ring and the
upper part of the holder and then properly fit the porcelain part of the holder
in the groove and then fit the holder again.
Sometimes the aluminum wire which is being used these days,
inside the holder connected to the terminal gets burnt or broken and therefore,
lamp does not give light. In such a condition, open the holder and connect the
wires in the holder terminals properly.
It is seen that there
are two wires connected to the holder (neutral and half) and sometimes there
are three wires (Two neutral wires joined together and half); the two neutral
wires joined together should not be opened and if opened, same wires should be
joined together which were opened. If the holder, switch and the lamp are in
order, then the defect lies in the wiring.
Construction of
fluorescent lamp
Low pressure mercury lamp is a long evacuated tube. It contains
a small amount of mercury and argon gas at 25mm pressure since at the time of
switching in the tube.
Mercury is in the form of small drops, therefore to start the
tube filling up of argon gas in necessary. So, in the beginning argon gas
starts burning at the ends of the tube, the mercury is heated and controls the
current and the tube starts giving light.
At each end of the tube, there is a tungsten electrode which
is coated with fast electron emiting material. Inside of the tube is coated
with phosphor according to the type of light and other accessions to be
connected with the lamp. It helps to start the tube. The starter breaks the
circuit. These are of two types.
1.
Thermal
type
2.
Glow
type
Thermal type
In this type of starter there are two contacts and one
heater. In the beginning the two contacts are close, the current flows through
the electrodes and the starter heater is heated.
Because of the heat
produced in the heater the two contacts of the starter are separated and the
tube starts working. So long as the tube is working, the current keeps on
passing through the heater and the contacts remain open.
Because of continuous flow of current in the heater, there is
wastage of power. These types of starters are not in common use. Thermal
starters are good for use on D.C. supply.
Glow type
In this type of starter, there are two bimetal (made of two
different materials) strips. These strips are enclosed in an evacuated glass
tube which contains helium at low pressure.
In the beginning, the two strips are separated apart. If the
connections are made the full voltage is applied across the strips, the helium
gas inside it starts glowing. Because of this glow the strips are heated and
joined together. Now there is complete series circuit, the gas does not glow
and the strips get cooled and are thus separated apart, the tube starts working
and the current flows now through the mercury electrons inside the tube.
A condenser is connected across the strips so that there is
no interference in radio sets at the time of opening and joining these strips.
Choke coil
It is also called blast. It has a laminated core over which
enameled wire is wound. The function of the choke is to increase the voltage to
almost 1000V at the time of switching on the tube and when the tube starts
working, it reduces the voltage across the tube and keeps the current constant.
According to tube principle, the electrons keep on colliding
with atoms, thus producing more electrons. More electrons mean more current
flow. If the excessive increase in the electrons is not checked the current can
increase to high value.
The choke keeps the current flow uniform. As the current
increases, the voltage across choke terminals (IZ) will increase which will
reduce the voltage across tube terminals and thus the production of electrons
will be less which will reduce the current.
This reduction in
current will decrease the voltage (IZ) across the choke which will increase the
voltage across the tube terminals. This in turn will again increase the current.
This cycle is repeated because of quick repetition of this cycle, the light
emitted by tube remains.
This in turn will again increase the current. This cycle is
repeated. Because of quick repetition of this cycle, the light emitted by tube
remains uniform.
Defects in the tube
light
Lamp does not glow
The following reasons may be there
i.
Broken
or loose connection: Test the supply at the lamp holder connects one end of the
test lamp to the pin of one holder and the other to pin of the starter.
Sometimes the pin gets inside and there is no proper contact.
ii.
The
gas may have leaked out of the lamp or the filament may be broken. Test is
given ahead. Choke may be defective. Test is given ahead
The filament glows but
the whole tube does not give light
The starter contacts may be welded. Test is given ahead.
Tube twinkles
i.
It
is possible that the life of the tube is over.
ii.
The
supply voltage may be low: Nothing can be done make a complaint to the electric
supply undertaking.
iii.
New
tube may be defective: connect the tube on some other circuit. If it is
detective, then replace the tube.
iv.
Starter
may be defective: Test of starter is given ahead.
Gas is seen whirling
inside the tube
This phenomenon occurs with a new tube. To correct this,
switch off the tube for a while and then again switch on.
It takes time for the
tube to give light
i.
Low
supply voltage
ii.
Choke
may be defective
iii.
Starter
may be defective
Electrodes get burnt
when the tube is switched on
Wrong wiring or choke may be there in the circuit. Tube
circuit has already been given. Compare the circuit and correct it.
Tube life is less
i.
More
supply voltage.
ii.
Defective
choke test it.
Tube ends are blackened
and the tube light twinkles
Tube life is over. Replace the tube.
The tube gives small
light at night even after switching off
Phase wire is directly connected to the tube and it is not
though the switch. This wrong connection is mostly at the meter board. Switch
off all the lights.
Now connect one end of the test lamp to the earth point of wall socket or to any other earth point and the other end of the rest lamp to any of the wall socket. If the test lamp gives light, then interchange the lead wires at the meter board. The phase wire will now be connected to the tube through the switch.
Reviewed by knowledge people creators
on
September 22, 2021
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