Contactor
A contactor is an electrical device used for switching an electrical circuit on or off. It is similar to a relay, but the main difference is that the contactor is applied in high-current carrying capacity applications, and the relay is used for low-current applications.
There are various types of contactors, and each type has its own set of features, capabilities, and applications. Contactors can break current over a wide range of currents, ranging from a few amperes to thousands of amperes, and voltages from 24 VDC to thousands of volts. In addition, these electrical devices come in various sizes, from palm dimensions to sizes Measuring a meter or yard on one side (approximately).
The most common application area of the contactor is high-current load. Contactors are known for their capability to handle currents of over 5,000 amperes and high power of over 134HP.
Main Components of the Contactor
The Electrical contactor has three (3) main components namely the
(i) Coil (Electromagnet)
(ii) Enclosure
(iii) Contacts.
The Coil or Electromagnet provides the driving force that is required to close the contacts of the contactor. The coil and contacts are protected by an enclosure.
The enclosure provides insulation and protection from personnel touching the contacts. The protective enclosure is made from different materials, such as polycarbonate, polyester, Nylon 6, Bakelite, thermosetting plastics, and others.
The contacts of the contactor are responsible for carrying rated current to the load the contactor powers. There are different types of contacts in a contactor namely, contact springs, auxiliary contacts, and power contacts. Each type of contact has an individual role to play.
Operating Principle of a Contactor
When current is supplied to a contactor, the electric current excites the electromagnet. The excited electromagnet produces a magnetic field, causing the contactor core to move the armature as shown in our schematic below:
A normally closed (NC) contact completes the circuit between the fixed contacts and the moving contacts. This permits the current to pass through these contacts to the load. When the current is removed, the coil is de-energized, and the circuit is open. The contacts of the contactors are known for their rapid open and close action.
One unique quality of contactors is that their coils can be powered by both DC and AC currents. Typical voltages include 12VDC, 24VDC, and 220V AC with the most popular in use being the 24V DC for many control circuit applications. Contactors are primarily used for controlling single and three-phase motors and switching power circuits.
Contactor Standards
There are two standards for contactors: NEMA and IEC.
NEMA Contactors
NEMA means National Electrical Manufacturers Association. NEMA contactors also are designed with safety factors that go beyond design ratings (oversized), up to as much as 25%. NEMA is primarily a North American Standard. NEMA contactors for low-voltage motors (less than 1,000 volts) are rated according to NEMA size, which gives a maximum continuous current rating and a rating by horsepower for attached induction motors. NEMA standard contactor sizes are designated 00, 0, 1, 2, 3 to 9
IEC Contactors
IEC means International Electrotechnical Commission and it is a global standard. IEC contactors are not oversized. They are smaller than NEMA contactors and less expensive. The range of sizes offered by manufacturers is more numerous than the ten NEMA standards. As such, they are more specific to a given application and are specified when the operating conditions are well understood. Whereas NEMA may be chosen when operating conditions, such as load are not well defined.
Difference between NEMA and IEC Contactors
Below is a comparison between NEMA and IEC contactors already discussed:
IEC
NEMA
Less Expensive
More Expensive
More Compact
Larger design
Global Market
North American Market
Less versatile: IEC contactors are specific application requirements
More versatile: A NEMA contactor can cover a broader range of applications
Finger Safe
Safety covers required
Faster reaction to overloads
Can handle short circuits better.
Thank You !!!
IEC | NEMA |
Less Expensive | More Expensive |
More Compact | Larger design |
Global Market | North American Market |
Less versatile: IEC contactors are specific application requirements | More versatile: A NEMA contactor can cover a broader range of applications |
Finger Safe | Safety covers required |
Faster reaction to overloads | Can handle short circuits better. |