Siemens S5-135U/155U - Manual (Page 48)

3-22
System Manual
C79000-G8576-C199-06
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For 24 V DC load circuits, you require a load power supply unit with
safety separation. If an AC plug is used as the isolating device, the socket
must be in the vicinity of the central controller and easily accessible
(VDE 0805, 1.7.2).
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Unregulated load power supply units require a reservoir capacitor
Ã
(rated at 200 mF per 1 A load current). Connect the capacitor in parallel
with the output terminals of the load power supply.
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According to DIN VDE 0113, Part 1, control systems with more than five
items of electromagnetic apparatus require isolation by a transformer;
according to DIN VDE 0100, Part 725, it is recommended
Ä.
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Load power supplies should be grounded if possible
Å. Provide a
detachable connection to the protective conductor at the load power
supply unit (terminal L- or M) or on the secondary side of the isolating
transformer.
!
Caution
For ungrounded power supplies, you must provide insulation monitoring if⁄
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hazardous system states can be caused by double faults;
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there is no safety separation;
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circuits are operated with voltages of more than 120 V DC;
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circuits are operated with voltages of more than 50 V AC.
Load Power
Supply
Grounding
Installation Guidelines