A magnetic contactor is made up of a magnetic core (core and armature) and a coil that generates a strong magnetic field enough to overcome the forces of the springs that hold the two portions of the core apart. One of these components, typically the armature, is integrally coupled to the device and is in charge of activating the electrical contacts.
The following are the
device’s components.
1. Core
2. Armature
3. Coil or Electromagnet
4. Contact
5. Coil terminals
6. Spring
7. Enclosure
1) Core
The core is comprised of silicon steel sheets that are securely linked
together to prevent energy losses caused by current parasite
circulation. Its purpose is to house the coil, concentrate the
magnetic flux it generates, and attract the armour.
2) Armature
The armature is the electromagnet’s moving part. It is extremely
similar to the nucleus, however unlike it, it lacks turns of shade. Its
primary role is to close the magnetic circuit and drag the mobile
contacts with it.
3) Coil or Electromagnet
The electromagnet’s force of attraction is determined by the
magnetic flux that passes through it. An excitation coil placed in
one of the columns of the electromagnet core generates this flux.
The reels can be wound on an insulated resin spool.
Enamelled copper wire with a circular section is commonly used
for coil construction, and the procedures for making it are well
known. The coil characteristics are visible on the coil: voltage,
current class, and frequency in the case of alternating current
4). Contact
Contacts are classified into two categories.
a) Main Contacts and
b) Auxiliary contacts
a) Main contacts
The main contacts or poles are the contacts that act directly on the
load to be managed.
The main contacts are linked to the governing circuit. Ensures the
establishment and interruption of main currents, and depending
on the number of current paths (bipolar, tripolar, tetrapolar, etc.),
manoeuvres (movement) are carried out concurrently on all tracks.
b) Auxiliary contacts
Auxiliary contacts are classified into two types.
• Normally Open (NO contact)
• Normally Closed (NC contact)
These two types of contacts are part of the contactor’s auxiliary
circuit. It ensures the automation equipment’s self-supply,
controls, contact interlocks, and signalling.
The circuit between the network and the receiver is established
when the contactor coil is activated by current flow, causing its
core to move and drag its main and auxiliary contacts.
5) Coil Terminals
The voltage of the incoming power as well as whether the power
is derived from a single-phase or three-phase source determines
the size of coil terminals as well as the number of terminals.
6) Spring
The spring’s function is to keep the contacts open, which in turn
ensures that the load does not get any electricity. Either it will pull
from the other side or it will push the moveable contacts further
away from the yoke. There are other models that are created
specifically for vertical installation, and in those models, gravity
might take the role of the spring.
7) Enclosure
The enclosure ensures that all of the components remain
electrically isolated and protects users against unintentional
exposure. Plastic, Bakelite, or Nylon 6 are the three materials that
are used to construct the enclosure
Magnetic contactor Connecting
Before connecting, check the label value is appropriate for the
system to which are connected before connecting the equipment.
Then look for the A1 and A2 terminals. These terminals are known
as coil terminals. When the coil is energised, the contactor’s main
power contact closes. Connect A1’s phase (+) and A2’s neutral (-).
When an electromagnetic coil is energised, it produces an
electromagnetic field. As mentioned in construction, the movable
contact of a contactor is coupled to the armature (metallic rod) of
an electromagnet.
When an electromagnetic field is created, the armature experiences
a pull towards the fixed contact. The force produced by the coil
exceeds the force produced by the spring. Both contacts will stay
in this state as long as the coil is not de-energized.
When the coil is de-energized, the electromagnetic force becomes
zero, and the armature pulls back due to spring force. And then
return to normal (OFF position). The contactors are developed for
immediate ON/OFF operation.
The contactor coil’s input can be AC or DC, and in some
circumstances, the universal coil is employed as an
electromagnetic coil. The universal coils work on both alternating
current and direct current. A tiny amount of power is lost in the
contacts, which is reduced using an economizer circuit.
An arc is formed between the contacts as they are made and
broken. Because it raises the temperature of the contacts, this arc 
broken. Because it raises the temperature of the contacts, this arc may shorten the life of the contactor. Arc produces hazardous gases such as mono-oxide. As a result, different ways are employed to control and extinguish arcs.
broken. Because it raises the temperature of the contacts, this arc may shorten the life of the contactor. Arc produces hazardous gases such as mono-oxide. As a result, different ways are employed to control and extinguish arcs.
The contactors are chosen based on the load current and voltage,
the voltage control range, and the application category. Users can
use an ohm-meter to determine if the connection of contacts is open
or closed. Connect the ohmmeter between the input and output
contacts; if the meter reads infinite, the contacts are open; if it reads
zero, the contacts are closed.
Advantages of the Magnetic Contactor
• The ability to control a machine completely from many
control points or stations.
• Circuits connected to currents can be controlled at
extremely high currents.
• Technical personnel safety.
• Given that the manoeuvres (movement) are performed
from locations remote from the motor or other sorts of
loads.
• The command devices manipulate currents and voltages
that are or may be modest.
• Control and automation of complex processes in
equipment and machines.
Disadvantages of the Magnetic Contactor
• Magnetic contactors will not malfunction if they are
properly selected and utilised under normal operating
conditions. Contact wear and coil burn are the most typical
issues.
• If a large amount current is sent via the power connections,
they will become heated and stick together.
• A magnetic contactor, unlike a circuit breaker, is not a
safety device. When an overcurrent current flows through
a circuit breaker, it causes it to trip. Overcurrent flowing
through the magnetic contactors, on the other hand, causes
the main contacts to stick.
• Similarly, if the voltage provided to the coil terminal is not
nominal, the coil will burn. As a result, nominal voltage and
current values must be provided to the main contacts and
coil.
• To improve system protection, protection devices such as
overload relays and fuses must be employed in conjunction
with the contactor.
Applications of the Magnetic Contactor
• The motor starter is the most common use for a contactor.
It is utilised for industrial motor overload and short circuit
protection.
• Contactors are used to automate lighting in industrial,
commercial, and residential applications. Latch type relays
are employed in this application. Two coils are utilised in
this sort of relay. One is for open contact, and the other is
for close contact.
• Single pole contactors are utilised to power the vehicle’s
12VDC load.
• The usage of contactors in conjunction with a circuit
breaker ensures the safety of load operation in industries.
In this application, it is used to switch a load quickly.
• It is employed in mercury relays as well as mercury-wetted
relays.
• To run 240VAC loads such as air conditioners, two-pole (3-
wire, 1-phase) contactors are employed.
Magnetic contactor parameter selection
The following technical parameters influence the selection of a
magnetic contactor:
• The type of load i.e., motor, heating, lighting, and air
conditioning
• Rated current and rated power.
• Voltage used in operation.
• Voltage control.
• The total number of poles.
• Internal auxiliary contacts availability.
Magnetic Contactor Types
Magnetic contactors are classified into different categories.
1. Knife Blade Switch Contactor
2. Manual Contactor
3. Alternating Current (AC) Contactor and
4. Direct Current (DC)Contactor
1) Knife Blade Switch Contactor
Electric motors turned on and off with this contactor. It’s a lever-
equipped metal strip. Metal strips are pulled up and down using
the lever. It’s manual. It’s hard to manually switch on and off
quickly. Wearing out contacts is possible.
In large motors whole load current passes through the contacts,
thus it’s high. Arc generation between contacts is difficult to
quench in this condition. The second issue is power loss. Due to the
high current, the connections will waste a lot of power.
Safety is the third issue. Therefore, this form of contactor needs
modification. Due to moisture damage, this contactor has a short
lifespan. Due to operational issues, this contactor is rarely used.
2) Manual Contactor
Manual Contactor is also called double break contactor. This
contactor is safe for smaller units. It lets to use more current in less
area. Double break contacts split the connection into two sets. As
its term indicates, manual control is required. The operator
manually turns on and off.
This contactor is the most advanced and so called automatic
electromagnetic contactor. Turning on and off the load requires a
simple control circuit. This contactor is safer than manual
contactors. Industrial applications use this contactor most.
Electromechanically, it connects load and power source with a
small current.
3). Alternating Current (AC) Contactor
Contactors used with alternating current are classified into four
types based on the nature of the load, and their applications are as
follows:
• AC 1 magnetic contactor
• AC 2 magnetic contactor
• AC 3 magnetic contactor
• AC 4 magnetic contactor
a). AC 1 Magnetic Contactor
This type of contactor is useful for resistive loads such as heaters
and electrical furnaces, as well as non-inductive or mildly
inductive loads, whose power factor ranges from 0.95 to 1.
b) AC 2 Magnetic Contactor
For the starting of motors with slip rings, it is used. As a slip ring
motor, this component is suitable for usage with loads that retract.
They utilise high torque current applications the most of the time.
c) AC 3 Magnetic Contactor
AC-3 Magnetic Contactor utilised in squirrel cage induction
motors for the purpose of performing disconnection operations
while the motor is operating at its maximum speed. The breaking
current is within acceptable limits.
d) AC 4 Magnetic Contactor
AC-4 magnetic contactor is used to start and stop an induction
motor with a cage. Squirrel-stopping in the starting, jogging, and
reversing by reverse.
4). Direct Current (DC) Contactor
The list consists of the various types of DC contactors.
• DC 1 magnetic contactor
• DC 2 magnetic contactor
• DC 3 magnetic contactor
a). DC 1 Magnetic Contactor
DC-1 magnetic contactor is appropriate for inductive and rather
non-inductive loads, as well as resistance furnaces and heaters.
b) DC 2 Magnetic Contactor
The DC-2 Magnetic Contactor Dynamic braking, in which the
motor is disconnected while it is spinning rapidly in shunt
motors’s starting, plugging, inching.
c) DC 3 Magnetic Contactor
The DC-3 Magnetic Contactor is used for dynamic braking,
jogging, reversing with reverse gear, and starting series motors