Information regarding operating voltage is documented in the relevant instructions for use.
For example, the operating instructions for PNOZ X3 contain the following note:
Note regarding overvoltage category III:
If voltages higher than low voltage (>50 VAC or >120 VDC) are present on the unit, connected operator elements and sensors must have a rated insulation voltage of at least 250 V.
Units for which this note appears in the operating instructions meet PELV requirements in accordance with EN 50178.
Units for which this note does not appear in the operating instructions do not meet PELV requirements in accordance with EN 50178.