Last edit: 10/11/2023
THE DOUBT: What is a safety contactor and is their usage compulsory in a Safety related control circuit?
CONSIDERATION 1: There are 2 main types of contactors used in Machinery:
- Power Contactors: they must be in compliance with IEC 60947-4-1: Contactors and motor-starters – Electromechanical contactors and motor-starters
- Auxiliary Contactors: they must be in compliance with IEC 60947-5-1: Control circuit devices and switching elements – Electromechanical control circuit devices
Power contactors have Mirror Contacts, to monitor their Status, while Auxiliary contactors have Mechanically Linked Contacts.
Normally, all those contractors have the possibility, using a small screw driver for example, to close their Normally Open contacts. That is a risk! Imagine a person who entered a safeguarded area: all contactors are de-energised and therefore all relative movements are stopped. However, if a person opens the control panel and forces a contactor with a screw driver, a dangerous movement restarts and the person may be subject to a hazard (unexpected start-up).
That, of course, is a risk to be reduced. Normally that risk is reduced with a correct implementation of the “Control of Hazardous Energy” (ANSI Z 244-1) or “Prevention of the Unexpected Start-up” (ISO 14118).
CONSIDERATION 2: Since a few years, component manufacturers have added, so called, Safety Contactors to their range. Those are normal Power contactors, compliant with IEC 60947-4-1, without the possibility to force them to close, for example, with the use of a screw driver.
Normally, they are equipped with both Mirror contacts and Mechanically Linked Contacts; these latterss are normally mounted on the body of the contactor and are “sealed”: that guarantees they cannot be detached from the contactor main body.
CONCLUSION: Safety contactors are a recent product, added to the range of power contactors, by several component manufacturers. They have the advantage of making it impossible to operate them manually and they are normally equipped with both Mirror and Mechanically Linked Contacts.
Despite the fact that they have these advantages compared with normal contactors, compliant with the same standards, their usage is not required by any functional safety standard. Moreover, their usage does not allow to reach a higher level of reliability. Statements like “with one safety contactor you can have SIL CL 2” are incorrect, since that is not supported by any current (2024) functional Safety Standard.
Therefore, you can decide to continue using normal Power Contactors in compliance with IEC 60947-4-1 in your Safety-related Control Systems.