XPost: sci.physics, alt.solar.thermal   
   From: vaughnsimon@gmail.invalid   
      
   "Morris Dovey"  wrote in message   
   news:j8lgpt$sc4$1@speranza.aioe.org...   
   >   
   > That will resolve the fused contacts issue, but leads me to ask a related   
   > question: If/when an SSR fails, does it fail open or does it fail closed?   
   >   
   The normal fail mode is closed.  I have used literally thousands of these   
   things   
   in traffic signals controllers.  In practice, they seldom fail randomly and are   
   at least as reliable as a mechanical relay (which can fail open OR closed)..   
   High current from a short circuit or a zap of lightning were the usual culprits   
   that caused failure.   
      
   Vaughn   
      
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