JSNA MLC Series Mechanically Linked/Force Guided Relays

Positive Guided Contacts

Positive guided contacts are a requirement in safety circuits to correctly monitor the status of normally open contacts. Guided contacts imply that Normally Open (NO) and Normally closed (NC) will operate together reciprocally but can never be simultaneously closed, even if the NO contacts weld. This requirement is obtained by particular constructional details, such as reduced gap tolerance through which the mobile contact travels and the points of actuation are closer to the actual contact position.

Positive Guided Contacts are also called positive safety contacts, forced contacts, linked contacts, force or positive guided or positively driven contacts.

The positive guided contacts assume different meanings and terminologies in compliance with the product standards which are given below.

IEC 60947-5-1/A2 ed. 2 - Annex L

In this case, positively guided contacts are called mechanically linked contacts. The requirement is that NO and NC contacts can never be simultaneously closed, even if the NO contact or NC contact welds in closed position.

This requirement applies to auxiliary safety contacts included in control circuit devices where the actuating positively is provided internally; therefore, this does not apply to push buttons or limit switches. The JSNA MLC series relays, as well as the auxiliary add-on contact block, fall into this category. Symbol to identify a mirror contact is shown below.

Mechanically Linked Contacts

Physical Properties of Mechanically Linked Contacts

Note: Control circuit devices, operated externally (e.g. push-button or limit-switches) can not have mechanically linked contact elements. Such devices, in safety applications, generally have contacts with Direct Opening Actuation.