7.5.2 Requirements for the power supply
External 24 V power supply
Power is supplied to the NCU by an external 24 V power supply (e.g.: SITOP). The following
power consumption values for an NCU provide a conguration basis for calculating the 24 V DC
power supply.
Table 7-3 Input voltage specication
Typ. current consumption
1)
Max. power consumption
2)
NCU 710.3B PN 0.9 A 11.7 A
NCU 720.3B PN 0.94 A 14.6 A
NCU 730.3B PN (PLC 317) 1 A 14.6 A
NCU 730.3B PN (PLC 319) 1.25 A 15 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
Danger of death caused by unsafe power supply
The DC power supply must be implemented as a circuit of Category PELV/DVC A according to EN
61800-5-1.
WARNING
Inadequately fused supply cables can be life-threatening
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 NCU 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 DC power supply requirements in accordance with EN 61131-2
Rated voltage 24 V DC
Voltage range (average value) 20.4 V DC to 28.8 V DC
Voltage ripple peak-to-peak 5% (unltered 6-pulse rectication)
Booting time at POWER ON Any
Non-periodic overvoltages ≤ 35 V
Duration of overvoltage ≤ 500 ms
Connecting
7.5 Power supply
NCU 7x0.3B PN
Equipment Manual, 10/2020, 6FC5397-1EP40-6BA1 53
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