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