Festo 14 Mode D'emploi page 19

2.3 Fitting the electrical components
Warning
When using valves with DC 12 V or DC 24 V control
voltage:
S Use only power units which guarantee reliable
isolation of the operating voltages as per IEC 742/
EN 60742/VDE 0551 with at least 4 kV isolation
resistance (Protected Extra Low Voltage, PELV, see
adjacent symbol). Switch power packs are permitted,
providing they guarantee reliable isolation in
accordance with EN 60950/VDE 0805.
By the use of PELV power units, protection against electric
shock (protection against direct and indirect contact) is
guaranteed in accordance with EN 60204−1/IEC 204.
Safety transformers with the symbol shown above must be
used for supplying PELV networks. The valve terminal must
be earthed to ensure that it functions correctly (e.g. EMC).
Festo VDMA−02−ZR.. 0403a English 19