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Old September 23rd, 2018, 10:10 AM   #1
PL_c
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Common ground or 0V

Hi, I have two different power supplies.
First 5A DC, second 20A DC

I will use them for PLC's.

How i should connect them together.

Please look at pictures.

Thank you.
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Old September 23rd, 2018, 10:31 AM   #2
damica1
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You don't have to connect together, however, if you need the same "Reference Point" for both then you should connect as shown in figure 2.
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Old September 23rd, 2018, 10:59 AM   #3
mike3475
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you never need figure 1 ,since the 24V power suply primary side always isolated with secondary side +24V.

Last edited by mike3475; September 23rd, 2018 at 11:01 AM.
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Old September 23rd, 2018, 11:03 AM   #4
PL_c
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I use seperate plc’s who are power supplied from different power supplies and these plc’s share with each other inputs/outputs.
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Old September 23rd, 2018, 11:34 AM   #5
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Any power supply output needs a reference to ground. It can not be floating.
If it were floating and its cables pass next to other cables with strong dv/dt like those that use PWM, voltages in the range of thousands volts can be induced respect to earth in the floating side.

For avoid this the usually way is to connect the 0V output to ground but only at one point, usually at power supply output terminal, but never use the ground circuit as power supply common. The common must be a separate wire.

Of course to achieve this the power supply must have the output isolated from input. The same applies for transformers.
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Old September 23rd, 2018, 08:21 PM   #6
kalabdel
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I don't get the purpose of #1 as both supplies are wired to the same neutral anyway, according to the schematic.

As for connecting both output commons together, yes if they share devices. An example is analog sensors powered by G1 and their output is connected to PLC inputs that is powered by G2. In that case both PLC Analog sensors need to share the same reference point/common.
And as Ife stated grounding has to also be considered.
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Old September 23rd, 2018, 10:00 PM   #7
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Quote:
Originally Posted by kalabdel View Post
both PLC Analog sensors need to share the same reference point/common.
correction:

both PLC and Analog sensors need to share the same reference point/common.
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