Protective switching device and method

A method for protecting an electrical low-voltage circuit for a protective switching device, the method comprising:

• providing a mechanical isolating contact unit connected in series with an electronic interruption unit;
• wherein the mechanical isolating contact unit is switchable by opening contacts in order to avoid a current flow or closing the contacts for a current flow in the low-voltage circuit;
• and
• wherein the electronic interruption unit is switchable, by semiconductor-based switching elements, into a high-impedance state of the switching elements in order to avoid a current flow or into a low-impedance state of the switching elements for the current flow in the low-voltage circuit;
• determining a level of the current in the low-voltage circuit and, when the level of the current exceeds at least one current threshold value, initiating an avoidance of a current flow in the low-voltage circuit by switching the electronic interruption unit to high impedance;
• and
• with a high-impedance electronic interruption unit, or a switching of an electronic interruption unit into a high impedance state, still determining the level of the current in the low-voltage circuit and initiating an opening of the contacts of the mechanical isolating contact unit only if a first fault current threshold value is exceeded.

A protective switching device for protecting an electrical low-voltage circuit, the protective switching device comprising:

• a housing having first and second connections for conductors of the low-voltage circuit;
• a series circuit of a mechanical isolating contact unit and an electronic interruption unit, said series circuit electrically connecting said first and second connections;
• said mechanical isolating contact unit being configured for switching by opening contacts in order to avoid a current flow or closing the contacts for a current flow in the low-voltage circuit;
• said electronic interruption unit being configured for switching, by way of semiconductor-based switching elements, into a high-impedance state of said switching elements in order to avoid a current flow or into a low-impedance state of said switching elements for the current flow in the low-voltage circuit;
• a current sensor unit for determining a level of the current of the low-voltage circuit and for providing instantaneous current values;
• a control unit connected to said current sensor unit, to said mechanical isolating contact unit and to said electronic interruption unit, wherein, when the level of the current exceeds at least one current threshold value, said control unit initiates an avoidance of a current flow in the low-voltage circuit by switching said electronic interruption unit to high impedance;
• and
• wherein, when said electronic interruption unit is in a high impedance state and only if a current in the low-voltage circuit exceeds a first fault current threshold value, an opening of contacts of said mechanical isolating contact unit is initiated, and said first fault current threshold value is lower than the current threshold value.