Help understanding the contact ratings in a Schneider electric Zelio relay specification
The relay contacts will switch whatever voltage you apply to them, but you should not use them to switch a higher voltage than their rating.

The contacts on the relay you show can be used in a 5 Volt DC circuit, or 12 Volt, or 24V, or anything else under 30 Volts.

A relay has two parts, each of which has its own voltage and current rating.

The relay coil ratings give the voltage and current required to move the relay switch contacts - this could be called the input voltage, coil voltage or control voltage.

The contact rating gives the maximum voltage and current that the switch contacts are designed to handle.  I don't like the terms "secondary voltage" or "output voltage" for the contact voltage rating (and DEFINITELY NOT "control circuit voltage"!! - that would be the coil voltage).  The relay switches a voltage you provide - it does not provide any voltage to the controlled circuit.  

A relay can be thought of as an electrically-operated switch.