Should you use solid-state or electromechanical relays?

Choosing between SSRs and EMRs involves multiple considerations.

By Mike Bacidore, chief editor

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Sometimes, choosing a component is up to the customer’s discretion. Sometimes, it’s based on the application. And sometimes it’s just what the machine builder is most familiar with. With relays, there are a few clear-cut ways to go, but many times it’s a matter of trade-offs. Choosing between electromechanical relays (EMRs) and solid-state relays (SSRs) is sometimes more difficult than you get credit for.

This panel of industry veterans will give you a few insights that might remind you of some basics you already know and could help you make a more-informed decision on your next machine.

Meet the panel

Tom Stevic100x100Thomas Stevic is controls engineer at Zed Industries, a thermoforming and plastic packaging machine builder in Vandalia, Ohio.



Steve Kirk100Stephen Kirk is project manager at Industrial Automation Group, a system integrator in Modesto, California.



Michael Collins100Michael P. Collins is president of MPC Management, a consulting company in Portland, Oregon.



Danny Weiss100Danny Weiss is senior product manager at Newark element 14.




Kurt Wadowick100Kurt Wadowick is I/O and safety product specialist at Beckhoff Automation.




Rafal Pabich100Rafal Pabich is senior product manager at Carlo Gavazzi Automation.




Dan Nigro100Dan Nigro is product marketing manager, industrial components, at Omron.




Steve Massie100Steve Massie is product manager at IDEC.




LoflinDan100Daniel M. Loflin is product manager at Siemens.




Tina Lockhart100Tina Lockhart is director of engineering at Moore Industries.




Terry Harmon100Terry Harmon is offer marketing specialist at Schneider Electric.




Rick Frauton100Rick Frauton is senior product marketing manager at United Electric Controls.




TomEdwards100Tom Edwards is senior engineer at Opto 22.




Traci Bretz100Traci Bretz is relay product marketing specialist at Phoenix Contact USA.




In which applications are electromechanical relays (EMRs) still more advantageous than solid-state relays (SSRs), and why?

Stevic: EMRs have several distinct advantages over SSRs when it comes to the power/cost ratio, switching voltage capabilities, power dissipation characteristics and failure mode. An EMR with a rating of 30 A can be had for as little as $10, where an SSR of the same power handling capability will cost about four to five times as much.

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  • There's no clear choice in this application area. Most of our comments center around personal preferences, anyway, so the commentaries ( mine included ) will be fraught with bias. This isn't, nor should be something around which we base our decisions in terms of, "political correctness", and yes, I see that as a possibility. Electro-Mechanical Relays - Good Points: 1.) Good for general-purpose switching. 2.) Superior isolation. 3.) Relatively easy to procure. Electro-Mechanical Relays - Bad Points: 1.) Life cycles less than solid-state relays. 2.) Switching times are longer than their solid-state counter-parts. 3.) Can weld shut under significant over-load conditions. Solid-State Relays - Good Points: 1.) Shorter switching times, as compared to their electro-mechanical counter-parts . 2.) No inductive kick-back to contend with. 3.) Low switching power consumptions. Solid-State Relays - Bad Points: 1.) Costs are significantly-greater than their electro-mechanical counter-parts. 2.) Load switching potentials are specific - no lee way. 3.) Special precautions are required when switching the input of a solid-state device: I.E.: a TRIAC-based SSR switching a 120-VAC PLC input requires a snubber resistor to keep the quiescent voltages low-enough to prevent a false, "On" state. In closing, it's really a matter of personal choice. The application does need to be considered, but there's no reason to lay-around a grape-laden table in a Toga with your peers, and have a discussion reminicent of ancient Pathos, Greece.


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