1.2 Application planning
1.2.1 Secondary electrical conditions
1.2.1.1 Power supply
Requirements for 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 NC 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 NC cabinet (also refer to /EMC/EMC Installation Guide.)
Table 1-1 Requirements of the DC power supply
Rated voltage According to EN 61131-2
Voltage range (mean value)
Voltage ripple, peak/peak
Powering up time when switched
on
24 VDC
20.4 VDC to 28.8 VDC
5% (unsmoothed 6-pulse recti‐
fication)
any
Non-periodic overvoltages
Period of overvoltage
Recover time
Events per hour
≤ 35 V
≤ 500 ms
≥ 50 s
≤ 10
Transient voltage interruptions Downtime
Recovery time
Events per hour
≤ 3 ms
≥ 10 s
≤ 10
General information and networking
1.2 Application planning
Operator panel front: OP 012
Manual, 09/2016, A5E36371591B 11
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