BECKHOFF CX50x0 - Manual (Page 33)

Notes on the documentation
CX50x0 - Hardware Documentation 31
UL requirements
Danger
For the compliance of the UL requirements the CX-Controllers should only be supplied
 by a 24 V
DC
supply voltage, supplied by an isolating source and protected by
means of a fuse (in accordance with UL248), rated maximum 4 Amp.
 by a 24 V
DC
power source, that has to satisfy NEC class 2.
A NEC class 2 power supply shall not be connected in series or parallel with
another (class 2) power source!
This UL requirements are valid for all supply voltages of the CX-Controllers!
To meet the UL requirements, the CX-Controllers must not be connected to unlimited
power sources!
PE power contacts
Attention
Power contact "PE"
The ”PE" power contact must not be used for other potentials.