A safety circuit shall contain a control relays and/or contactors with positive-guided contacts used for switching power to the load. Each relay or contactor shall have at least one N/C contact in the restart circuit which is used for self-checking. This N/C contact remains open in the event of weld power contacts of the relay/contactor, and prevents the safety circuit from restarting. This type of contacts is commonly called Mechanically Linked or Positively Guided.

Conventional multipurpose relays and/or contactors cannot be used for this purpose. After a conventional relay contact welds, and the relay de-energizes, the N/C contact is allowed to return to the closed position. The safety circuit has no way of "knowing" that a contact weld has occurred, and the machine is allowed to restart.

General Safety Company can offer a full range of Control Relays (up to 10A) and Contactors (up to 400A AC3) with Mechanically Linked or Positively Guided built-in or auxiliary contacts. They meet the requirements of the Mechanically Linked or Positively Guided contacts described in the IEC 60947-4-1 Annex F and IEC 60947-5-1 Annex L Standards. All relays and contactors are CSA certified or cUL listed.