8.5.2 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 VDC
power supply.
Table 8-3 Input voltage specication
Typ. current consumption
1)
Max. power consumption
2)
0.65 A 11.1 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
WARNING
Electric shock as a result of an unsafe DC power supply
If an unsafe DC power supply is connected, exposed components may be at a hazardous
voltage level, which can result in serious injury or death.
• As DC power supply, use a Category PELV/DVC A circuit according to EN 61010-1.
WARNING
Electric shock due to inadequately protected power supply cables
If power supply cables are inadequately protected, then lightning strikes can result in a surge
voltage. This can result in death, serious injury and material damage.
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. This
connection is normally provided as standard in the S7-1500 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 8-4 DC power supply requirements according to EN 61131-2
Rated voltage 24 V DC
Voltage range (average value) 20.4 VDC to 28.8 VDC
Voltage ripple peak-to-peak 5% (unltered 6-pulse rectication)
Ramp-up time at POWER ON Any
Non-periodic overvoltages ≤ 35 V
Connecting
8.5 Power supply
NCU 1740
64 Equipment Manual, 10/2021, A5E51087503B AA
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