The relay and the contactor are used depending on certain parameters to protect the system it operates. It is used in electrical panels and electronic circuits. They act as an electronic switch between the systems to which they are connected. While one of the circuits operating in the system is activated, the other circuit is disabled.
The relay is always used in circuits with low currents. The contactor is used in high-current circuits. Also, contractors are used to switch power circuits and electric motors. The working principles of the relay and the contactor are the same. They are circuit elements that do not work unless current flows through them. They cannot be manually operated and require external force to open and close. Their structures may vary according to the working areas. The contactor works depending on the current and voltage level that will pass over it, thanks to the structure inside the contact. It is not affected by different frequency and electrical signal structures. It also prevents mechanical failures. They can also be used to, for example, protect the running system from the harmful effects of high temperature or magnetic fields.
Contactors and relays are divided into types according to their working principles, current level to operate or manufacturing situation. Contactor types are divided into; AC Contactor, DC Contactor, Electromagnetic Contactor, and Compressed Air Contactors. The relay types are diversified as; Reactive Power Control Relay, Motor Safety Relay, Voltage Protection Relay, Leakage Current Relay and Time Relay.
Leakage Current and Leakage Current Relay
Leakage current is caused by the use of poor insulation material, poor electrical wiring work, or lack of proper grounding. Apart from all these cases, it can also be caused by the high ground line resistance and the contact of the cable connected to the ground line with another place. These moments can be dangerous for human life. If the leakage current in the electrical installation is over 30mA, the person caught in the electric current may be injured. Therefore, the response time of the relay is very important. In case of an imbalance between phases and neutral, the relay opens the circuit. If the current in the circuit is equal to the output current, there is no leakage in this circuit.
A residual current relay is used to protect systems from potential leakage currents. For example, in Turkey, TEDAŞ mandates and controls the use of residual current relays in distribution boards. The use of residual current relays is an important precaution to protect systems and their users. If leakage current occurs in the circuit to which the residual current relay is connected, an electromagnetic force occurs on the coils of the residual current relay. The resulting force activates the relay after a certain minimum point and cuts off the energy transmission within seconds. This keeps the circuit and users safe until the leak is fixed.
Motor Protection Switch
The motor protection switch is a circuit protection element like an electronic fuse. The motor protection switch is a kind of circuit protection element like an electronic fuse. While fuses usually only protect the power line, motor protection switches protect the electric motors to which they are connected. It has a three-pole electromagnetic structure. It provides protection against short-circuit current, phase problems, and instantaneous overcurrents. It is connected in series with the motor protection circuits. The motor protection switch can protect the motor against possible damage in a very short time. The use of thermal relays and fuses used as magnetic protection is rapidly decreasing with the use of motor protection switches. In addition, thanks to the motor protection switch, it saves material and space in electrical panels.
Motor protection switches can change according to the manufacturer’s model. It has a rotatable button or a pushing button. The motor protection switch should be selected according to the power of the motor in the system to be used.
Weak Current
The current, like a voltage, varies according to the amount of units to be used, and weak current is one of them. Weak current is generally used in communication areas with signaling use such as telephone, bell, antenna, security alarm, announcement system, alarm system. It reaches from weak current panels in buildings to sockets used in homes. Sockets known as telephone line distribution box, antenna jack and internet jack in homes are classified as weak current. It is used under medium voltage (1kV). In the cable grouping, low voltage cables contain weak current cables. Weak Current cables should have certain features according to their usage areas. It should be highly insulated and should not harm any living thing or product anywhere and under any circumstances. For this reason, cables usually contain gelatin and aluminum as insulating materials.
