Solid State Auxiliary Relays and Electromechanical Auxiliary Relays-A comparison

  Solid State Relays Electromechanical Relays
Noise No Noise Noise due to contact switching
EMI No EMI as no switching is involved EMI due to arcing during switching
Zero Voltage switching Possible Not Possible
Resistance to shock They are resistant to shock and vibration These relays can be affected by shock and vibration.
Temperature sensitivity Sensitive to Temperature less sensitive to temperature
Heat Generation Heat is generated due to higher resistance Low resistance in the contacts. Hence, less heat is produced
Heat dissipation Heat Sink is required Heat sink is not required.
Leakage Current Solid State Relays do not completely turn off.  There is a slight leakage Current.  This can affect downstream circuits. No leakage current.  The relays can be completely switched on or off.
Lifetime very long lifetimes. Relatively short lifetime