Title: +038=360.000-OU045T_03-PCD2.m4160 PLS SBC - Hardware Manual.pdf
When switching off load circuits with inductive components (e.g. relay coils and magnet windings), the break in current to the contacts causes an overvoltage (self-inductance voltage), which may be many times the operating voltage and compromise the isolation of the load circuit. The resulting sparks will cause the relay contacts to wear out quickly. For this reason, the contact protection circuit is particularly important with inductive load circuits. The values for the RC combination can also be determined from the diagram, but for voltage U the overvoltage arising when the current is interrupted (measured e.g. with an oscillograph) should be used. The current can be calculated from this voltage and the known resistance against which it was measured.AIn suppression elements, suppression condensers conforming to VDE 0565 T1 Class X2 must be used. These condensers are switch-tolerant and designed for particularly high overvoltages. Direct operation at mains voltage is still possible.