Connection of inductive loads

Switching of inductive loads (relays, contactors, starters, electromagnets, electric motors, etc.) with the help of any relay can cause an arc discharge when opening the contacts, which causes electromagnetic interference, which can lead to failures and damage to various electrical equipment.
Additional measures must be taken to reduce the level of electromagnetic interference to connect the inductive loads to the relay outputs of Atom devices. Some of the most common and effective solutions are shown below in Pic. 1 for alternating current and in Pic. 2 for direct current.

Illustration

Pic. 1. Example of the connection diagram of the contactor ESC225 230VAC to the relay OUT17 of the Atom Argon device with additional damping links for AC circuits:
А. The varistor is parallel to the relay contacts. For 230V voltage, MOV varistors should be used for voltages not lower than 275 - 300 VAC and of a size sufficient to absorb the accumulated energy in the coil, which depends on its inductance. The use of varistors with significantly higher operating voltage reduces the efficiency of the unit. In this case, and for small inductions, a varistor with a diameter of 7 mm will be enough, but with higher load inductance should use varistors of 10, 14, 20 mm.
В. Varistor parallel to the load. The type is selected similarly to the one described above.
С. RC link parallel to the load. The values ​​of the resistance of the resistor and the capacitance of the capacitor can be selected using special nomograms. You can also determine the required values ​​by experimental method, analyzing the oscillograms of transients and selecting the elements of the link. It should be understood that increasing the capacitance of the capacitor and reducing the resistance of the resistor increases the load on the relay contacts when they are closed. The resistor must be 1-2 W and high voltage, and the capacitor is designed to operate in AC circuits, type X1, X2 with an operating voltage of at least 275VAC, or metal-film with a voltage of at least 630VDC. For low-power contactors shows good results link with 47 nF and 240 Ohms. For more powerful 100 nF and 100 ohms, such links can also be purchased as an assembly for easy installation.

Illustration

Pic. 2 Example of the connection diagram of the ERD225SDC 24VDC contactor to the OUT17 relay of the Atom Argon device with additional damping links for DC circuits:
А. Diode in reverse polarity parallel to the load. The type of diode is selected by the reverse voltage, which should be > 10 * U n, and the rated current > I n. Usually the FR107 diode with a rated current of 1A and a voltage of 1000V is sufficient for most loads. This scheme has a disadvantage, as it greatly increases the time of turning off the contactor, but this can usually be neglected. To reduce this effect, the diode is sometimes used in series with an additional resistor or zener diode connected in the opposite polarity.
В. The varistor is parallel to the relay contacts. The type of varistor is selected depending on the operating voltage for direct current 1.2 * U n and its size depending on the self-induction energy accumulated by the relay coil. The use of varistors with significantly higher operating voltage reduces the efficiency of the unit. For small inductions - a diameter of 10 mm will be enough, but for larger will have to use varistors with a larger diameter.
Today, manufacturers of switching equipment sometimes install protective links in their devices. This simplifies installation, but such devices usually belong to the equipment of the upper price range. You can often find protective RC links and varistors integrated in intermediate relays, contactors, high current starters. Some manufacturers offer these elements as an option for their devices, or as separate components for mounting in panels.
In general, the use of such simple recommendations when installing power equipment will greatly reduce the level of electromagnetic interference near critical and important devices in your electricity distribution box and allow them to work smoothly and for a long time.

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