NX1P i/o wiring

[Pauljm]

HI All,

A quick question for you guys. I am wiring an NX1P with power supply splice PF0630 and an extra digital input slice, output slice, analogue input slice and Rs485 slice. I was advised it is best to run 2 x 24vdc supplies- 1 for PLC power and 1 for i/o power. The reason for this i was told was if any noise was generated on the i/o 24vdc it wouldnt affect the  PLC 24VDC and hence the PLC bus. I now learn  the PLC 24vdc still supplies power for the built in i/o. To me this just makes it difficult having 2 separate supplies in the field for i/o. So my question is- do you guys normally run 2 power supplies as described? If only one have you had any issues?

Thanks for any help as always.

Regards,

Paul

[IO_Rack]

Power isolation is always a good idea. I've actually used 3 separate power supplies on some applications. For this case, I was running 8 servo axis, remote EtherCAT I/O and driving many solenoids and safety devices. One power supply for powering devices, one for inputs and a 3rd for outputs.

For medium applications I'll use 2. One for powering devices and inputs. The 2nd one for outputs.

For small, low power applications, I'll use 1 power supply.

In my opinion, it's not the type of PLC used but more the type of outputs used. If your outputs have a heavy current draw or are heavy with Back EMF, then you'll want to separate them with their own power supply.

Yes, I've seen problems. I've seen MCR contactors reboot PLCs when the EStop was activated. I've seen motor contactors reboot PLCs when cycling.

[Pauljm]

Hi and thanks for the reply Io rack. I guess my main issue with it is the Inputs on the main plc have to be driven by the plc supply but the inputs and outputs on the slice have to be either driven by that same power supply or a seperate one altogether. As far as I am aware There  is no option to seperate the slice inputs power supply from the slice outputs power supply. When using multiple supplies do you tie the 0v’s together or does this defeat the purpose?

Cheers...Paul

[Crossbow]

In most cases I've seen them installed, they use one power supply for both.  Exception being safety I/O, where they will use both a PF0630 and PD1000 to restart both power buses with the safety power supply.

[IO_Rack]

On ‎11‎/‎1‎/‎2019 at 6:08 PM, Pauljm said:

When using multiple supplies do you tie the 0v’s together or does this defeat the purpose?

This could be a long discussion with differences of opinion.

If the power supplies and all devices are truly isolated then it would not matter because they would never interfere with each other. Right? If the 0vs are not tied together then the supplies could possibly be at different potentials. This could cause a lot of problems if their paths ever crossed even if were just leakage. I would suggest searching the internet if you are interested in more details.

I believe the consensus is, yes, tie the 0vs together. It does not defeat the purpose. The supplies voltages will still be separated, they will just share a common reference. That's my opinion.