Note
NE 21 and IEC 61131-2
For compliance with NAMUR Recommendation NE 21 and IEC 61131-2, use only power
supplies (230 V AC --> 24 V DC) with bridging of supply failures of at least 20 ms. You can find
up-to-date information on PS components on the Internet (http://
mall.automation.siemens.com).
Connecting power supply (X80 and X81)
Table 7-1 Connection of supply voltage (plug with screw-type terminals / connection scheme / plug
with push-in terminals)
Plug with screw-type terminals Connection scheme (CFU PA ex‐
ample)
Plug with push-in terminals
1L+: Supply voltage: 24 VDC
1M: Supply voltage: Ground
2L+: Supply voltage: 24 VDC
2M: Supply voltage: Ground
x: Spring opener
Connect the M and L+ wires of a power supply to the connectors X80/X81.
● The power supply is connected using two 2-pin plugs (plug-in terminal blocks).
● A redundant power supply can be connected (plug connectors X80 and X81).
– Both inputs are decoupled.
– The ground connections of the plugs (1M and 2M) are connected to each other in the
CFU.
– There is no load distribution.
– With redundant infeed, the power supply unit with the higher output voltage supplies the
device exclusively.
● Two contacts each are located over each other for each potential (L+ and M). This ensures
that the power supply can be looped through (current: maximum 10 A).
● The power supply has a high-impedance connection with the housing to enable an
ungrounded installation.
Connecting
7.3 Connecting the power supply to the CFU
SIMATIC CFU
Commissioning Manual, 08/2019, A5E39252870-AD 57
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