Isolated and non isolated power supply

[otrotabi]

I am (hopefully) communicating 2 TM172PDG18R PLC´s via Can binding.  Since there is a difference in whether you should connect the PLCs (and I would not like to burn anything) I would like to make sure if I understand correctly.

From one of the first results in a google search, "An isolated power supply is a power supply that is electrically isolated from the rest of the circuit that it is powering, often by an isolation transformer."

In this case I am using 220-24Vac separate transformers to power up each PLC. So my guess is that I should connect the GND pin on the CAN port.

For other possible scenarios, using 2 switch power supplies would also require GND pins to be wired, while if only one power supply was used for both PLCs then GND cable should not be connected, as well as a hypothetical (but unlikely I would say) of using auto-transformers, then the GND cable should not be wired but you would have to make sure that neutral and live cables are connected alike in the auto-transformer input side.

Would you please comment ?

[Bastian_Schmitz · Accepted solution]

The description is in the new version of ESME HVAC easier. If you have two power supplies (each for every controller) wire GND. If you have one power supply and you use the TM172 Version with I you could wire GND.

If you use the old version TM172P**G**R then do not wire GND.

In my personal expirience I do not wire GND and I seen more problems with then without GND.

[Bastian_Schmitz]

As additional information TM172***18* has always a isolated power supply intgrated. So far you did not connect GND to ground you could connect GND between two controllers.

[otrotabi]

So, summing up: for TM172***18* (which is the case here) regardless of the external power supply there´s a built in isolated power supply ? That means do connect GND.

Also, I know nothing about how it is in the inside electronics an I was worried about maybe the grounds would at different equipotential, thus generating some issue, but it looks like you try first without GND and then if that does not work fine, connect it. Am I right ? 

Thanks for your help.