Solid State Relays vs Electromechanical Relays
Solid State Relays vs Electromechanical Relays
(OP)
I am not a controls engineer, but have been around electronics for several decades. The cost of Solid State Relays is three times that of Electromechanical Relays which have been around for ever. For this application, both must be Class I Div. II capable. My question is, why should I select solid state over electromechanical?





RE: Solid State Relays vs Electromechanical Relays
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RE: Solid State Relays vs Electromechanical Relays
Benta.
RE: Solid State Relays vs Electromechanical Relays
If you are switching at a lower pace like once or twice an hour or so, and perhaps quite low loads (a few hundred milliamps) then electromechanical relays usually have a life that exceeds life of the application (thinking ten - twenty years or so).
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Solid State Relays vs Electromechanical Relays
Always do the math for your application. That's how many times a unit-of-time you expect your relay to cycle and how many unit-of-times you want the relay to last.
I see this cluelessly ignored frequently. You can rack up a million cycles with once a minute cycles in less than two years. Cycle the relay faster than that and ...
On the other hand SSRs can last even shorter times if they don't get their considerable thermal issues handled well.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Solid State Relays vs Electromechanical Relays
A mechanical relay would have to be in an enclosure ($$) rated for Class I Div 1. It arcs and sparks in normal operation.
Of course, the best thing to do is mount the relay away from the hazardous area. Can you not stick it in the safe area and run conductors through a conduit seal into the hazardous area?
Best to you,
Goober Dave
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RE: Solid State Relays vs Electromechanical Relays
RE: Solid State Relays vs Electromechanical Relays
That is true in a Division 1 hazardous location (explosionproof enclosure required), but the OP wrote Div 2. Items that do not present an ignition source in normal operation may be installed as if in ordinary locations in Div 2. A mechanical relay would need a Div 1 enclosure even in Div 2, but the SSR should need no more than a NEMA 1 enclosure.
Best to you,
Goober Dave
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