Control circuits and auxiliary circuits

The increasing demands on machines and installations in terms of operational safety and accident prevention require comprehensive measures to protect both man and machine. For example, insulation faults in a control system must not lead to hazardous machine motions. Therefore, when choosing a system type (TN, TT or IT systems) and the associated protective measures, the following aspects are of particular importance:

• Probability of insulation faults
• Necessary basic protection and fault protection
• Continuity of the power supply
• Technical and commercial aspects
• Experience regarding secondary effects (fire, downtime costs, etc.)

In the case of electrical machines, this applies to the control circuits and auxiliary circuits as well as to the main circuits. In main circuits, the most important aspects are protection against electric shock, protection of persons and fire prevention. In control circuits and auxiliary circuits, especially those with voltages below the permissible touch voltage of AC 50 V/DC 120 V, the focus is on operational safety.