Siemens NCU 7x0.3 PN Series Manual page 47

Requirements of DC power supplies
The DC power supply is always referenced to ground and may not be generated by an
autotransformer.
Final user interfaces are powered via a DC power supply with protective separation per EN
61800-5-1.
In the case of supply lines > 10 m, protectors must be installed at the device input in order
to protect against lightning (surge).
The DC power supply must be connected to the ground/shield of the Control Unit for EMC
and/or functional reasons. For EMC reasons, this connection should only be made at one
point. As a rule, the connection is provided as standard in the S7-300 I/Os. In exceptional
circumstances when this is not the case, the ground connection should be made on the
grounding rail of the control cabinet; please also refer to /EMC/EMC Installation Guide.
Table 7- 4
Rated voltage
Non-periodic overvoltages
Transient voltage interruptions
Additional references
Recommended power supply units and tables for calculating power consumption for
interconnection with SINAMICS S120 modules can be found in the chapter entitled Control-
Cabinet Construction and EMC Booksize in the SINAMICS S120 Booksize Power Units
Manual.
NCU 7x0.3 PN
Manual, 09/2011, 6FC5397-1EP40-0BA0
DANGER
DC power supply requirements in accordance with EN 61131-2
Voltage range (average value)
Voltage ripple peak-to-peak
Booting time at POWER ON
Duration of overvoltage
Recovery time
Events per hour
Outage time
Recovery time
Events per hour
24 V DC
20.4 V DC to 28.8 V DC
5% (unfiltered 6-pulse rectification)
Any
≤ 35 V
≤ 500 ms
≥ 50 s
≤ 10
≤ 3 ms
≥ 10 s
≤ 10
Connecting
7.4 Power supply
47