'Safety' Contactors within the control system.

A question we are frequently asked is do Schneider Electric offer a ‘safety’ contactor?

The answer to this is that the term ‘safety contactor’ does not appear to have any clear definition within the Safety of Machinery standard IEC (BS EN) 60204-1 or within IEC (BS EN) 60947-4-1, the standard associated with contactors. Since there does not appear to be any clear definition of what is required from a ‘safety contactor’ we cannot confirm if there is such a product in the range. However, Schneider Electric does have contactor products with ‘mirror contacts’ that can be used to switch off the supply to a motor as part of a machine safety system.

Mirror contacts are defined within IEC (BS EN) 60947-4-1. The essence of the mirror contact function (refer to the standard for a full explanation) states that the N/C auxiliary contact on each contactor will not close when one of the power contacts is closed and can therefore be connected to a safety monitoring relay, such as a Preventa relay. Schneider Electric’s TeSys D contactors and TeSys U combined contactor circuit breaker ranges incorporate N/C mirror contacts in accordance with IEC (BS EN) 60947-4-1.

It is worth mentioning that prior to the introduction of mirror contact terminology, the requirement for reliable signaling from a N/C contactor auxiliary has, in some instances, been referred to as mechanically linked or guided contacts. Using this terminology to describe the requirements of a contactor can be misleading, as the definition of a mechanically linked or guided contact is the non-overlap of all N/O and N/C contacts. This terminology was originally used with respect to relays used in a variety of applications including railway signal interlocking. To claim this feature for a contactor without clarification is unwise as it implies that the condition of a very small auxiliary contact can influence the status of a potentially very large power contact controlled by a powerful electromagnet. Thus the introduction of the mirror contact specification that only considers the influence of the power contacts on the auxiliary and not the auxiliary on the power contacts.