Question: We intend to replace a control cabinet for a simple fan controller. As was customary at the time, its emergency stop function is implemented using a simple contactor, which is switched off via the emergency stop pushbutton. A contact on the contactor switches the controller off. Must an emergency stop control device be provided in the new design for the plant or can we use the same format as previously? Is it absolutely necessary for an emergency stop control device to be installed in new plants or can a "contactor version" still be used in "simple" plants?
Answer: In principle, an emergency stop function can be implemented via a pushbutton that acts directly upon a positive-guided contactor.
However, the level of this safety function is limited to one value, e.g. Performance Level c, (based on the description in the question we are assuming a 1-channel system.
If Performance Level C adequately fulfils the safety function, then it is not absolutely necessary to use a safety relay.