Connecting
7.4 Power supply
NCU 7x0.2
50 Manual, 02/2011, 6FC5397-0AP20-0BA0
7.4.2 Requirements for the power supply
External 24 V power supply
Power is supplied to the Control Unit by an external 24 V power supply (e.g., SITOP). The
following power consumption values for the Control Units provide a configuration basis for
calculating the 24 V DC power supply.
Table 7- 3 Input voltage specification
Parameters Values
Typ. power consumption
1)
2.0 A
Max. power consumption
2)
8.5 A
1)
NCU only (processor, memory, etc.)
2)
NCU with full load at all outputs (digital outputs, USB, DRIVE-CliQ, PROFIBUS DP etc.)
Requirements of DC power supplies
DANGER
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.
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