Switching Inductive Loads

When inductive loads are connected to the relays, a large counter electromotive force may occur when the relay actuates because of the energy stored in the load. These flyback voltages can severely damage the relay contacts and greatly shorten the relay life.

Limit these flyback voltages at your inductive load by installing a flyback diode for DC loads or a metal oxide varistor for AC loads, as shown in the following figure.

Contact Protection Using a Flyback Diode for DC Inductive Loads

Accounting for flyback voltages is particularly important for the NI SCXI-1160/1161/1163R modules. Refer to the switch module documentation for information on preparing the switch module to properly handle inductive loads.