Which relay - classic EMR or SSR?
Posted by      02/01/2019 17:37:11     Railduino 2.0


Each type of relay has its advantage and disadvantage

EMR - classic electromechanical

PROS: switches AC and DC voltage, no need for cooling, no leakage currents, etc

CONS: contact life, el. arc during disconnection of contacts, max. switching frequency, etc.

SSR - semiconductor relay

PROS: not subject to environmental influences, high service life, low EMI interference

CONS: for heavy loads it is necessary cooling, leakage current, higher price, etc..


In the case of the Railduino module, there are two possibilities of the relay

classic EMR - max. current 7A at 230V, not an inrush relay

semiconductor SSR - max. current 2A at 230V, inrush 30A

Relay outputs 3-6 and 9-12 of the Railduino module are designed for lower current loads - max. 5A output. Max. current 7A can only be used at outputs 1,2,7,8.


In the first place, it is necessary to clarify what type of load (resistive, capacitance or inductive) will be switched on/off and how much currents can be expected in the load.

In case of switching capacitance / inductive loads it is necessary to use either an external inrush relay with properly dimensioned contacts or SSR relays that can withstand high inrush currents or NTC limiting element which limits the starting current.