What does the standard say?
The use of a residual current device (RCD) is often prescribed by standards for different protection goals, e.g. as protection against indirect contact or as additional protection in earthed systems. In resistance welding according to DIN EN 62135-1 (VDE 0545-1) or IEC 62135-1, a residual current device (RCD) can be used for protection against electric shock in the event of a fault (indirect contact):
- Generally, in TT systems “For each circuit or part of the electrical equipment different from the welding circuit (...) for automatic disconnection of the power supply before the time of contact with a touch voltage can become hazardous” (DIN EN 62135-1 section 6.4.1.).
- “To provide protection in the case of a fault between input and the output circuits, in contact with the work-pieces” (DIN EN 62135-1 section 6.4.2.).