Double break contacts divide the connection in such a way that it forms two sets of contacts. The switch or button of the manual controller is not operated remotely and is attached to the controller physically. The power circuit is engaged once the manual controller is activated by an operator.
Once activated, it carries the electricity to the load. Soon, manual contactors replaced knife blade switches completely, and even today different variations of these types of contactors are being used.
The magnetic contactor does not require human intervention and operates electromechanically. This is one of the most advanced designs of a contactor, which can be operated remotely. Thus, it helps eliminate the risks involved in operating it manually and putting operating personnel in potential danger.
Only a small amount of control current is required by the magnetic contactor to open or close the circuit. This is the most common type of contactor used in industrial control applications. It is natural that the contacts are being opened and closed more frequently, the life of the contactor will decrease.
The opening and closing of the contacts create an electric arc, which generates additional heat. The continued production of these arcs can damage the contact surface. Furthermore, the electrical arcs cause pitting and burn marks, which eventually blacken the contacts. However, the black deposit or oxide on the contacts make them even more capable of conducting electricity efficiently.
Nevertheless, when the contacts get worn out and corroded to a large extent, then it is necessary to replace them. Thus, the faster the contact closes, the quicker the arc extinguishes.
This in turn helps to increase the life of the contact. The latest contactor versions are designed in such a way that they close very quickly and energetically. This causes them to slam against each other and produce a bouncing action as they rebound. This action is known as contact bounce. The contact bounce phenomenon creates a secondary arc. It is not only important to close the contacts quickly, but also to reduce the contact bouncing.
This helps reduce wear and secondary arcing. NEMA encouraged manufacturers to standardize on frame sizes to allow users to confidently specify, purchase, and install electrical components from different manufacturers without a lot of hassle and cross-referencing.
NEMA contactors for low-voltage motors less than 1, 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 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. People often mistakenly perceive NEMA contactors as more robust. In reality, this is due to their design being oversized. Contactors are often used to provide central control of large lighting installations, such as an office building or retail building. To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils.
One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts. Contactors can be used as a magnetic starter.
A magnetic starter is a device designed to provide power to electric motors. It includes a contactor as an essential component, while also providing power-cutoff, under-voltage, and overload protection.
A contactor is a special type of relay used for switching an electrical circuit on or off. Please enter an answer in digits:. Skip to content Home Technical Knowledge What is auxiliary contact in a contactor? What is auxiliary contact? Previous: Differences between Variable frequency drive and Soft starter.
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