Machine Design

A safer safety switch

Emergency-stop switches turn off machinery in case of potential damage or risk to life and limb.

IDEC safety switch
Conventional safety switch

But such switches can fail due to improper installation, damage during transportation, accidental removal of the contact block, and other reasons. The XA/XW Series of switches from IDEC Corp., Sunnyvale, Calif. (idec.com), surpasses current international standards on E-Stops to preclude such risks. Springs keep conventional E-Stop switches in the normally closed (NC) position, letting a machine run. An operator hitting the switch with too much force can break or dislodge a part, letting the spring-loaded contact stay closed and the machine continue to run. In XW/XA switches, a spring ensures NC contacts pop open if the switch is damaged. IDEC switches also use four contacts. Currently, many companies use E-Stops with three contacts; two contacts trip the power and the third alerts a safety-monitoring relay. The extra contact gives operators the option to add another circuit and qualifies the switches for Level-4 applications. The devices secure from the rear of the control panel, so buttons cannot be removed from the front. The switches use push/pull and push/turn reset methods, eliminating confusion when operators reset the switch.

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