1. Cut-off principle

1.1 Introduction

Although the principle used to interrupt the current in electromechanical devices may seem simple, since all that's required is to separate the contacts, cutting currents is a complex phenomenon involving many parameters.

In addition to the intensity of the currents to be interrupted and the mains voltage values, transient phenomena and the resulting stresses are highly dependent on the behavior of the devices, in particular on the arc that is established between the contacts, and on the mains reactions linked to the characteristics of the circuit upstream and downstream of the device.

We describe these two aspects in turn, and in paragraphs