Signals with separate commons

I have a control card for a conveyor system that I need to send a 24VDC run signal to. The conveyors and my control system have separate power supplies though. Is it ok to send 24V from my power supply to the card, which has a separate 0V common? Both power supplies have the 0VDC side bonded to ground.

You could probably get away with that since the commons are effectively tied together through ground but check to make sure the grounds are really common. I have seen systems where there was a significant difference between grounds.
The safe way to do it is to use an isolated relay contact closure from your system and use the 24vdc power from the remote system.

Ok thanks. Both DC power supplies are being powered from the same 220V source and will share a ground bar. Just figured this would save me some wiring and some relays but I didn't know if there was any other reason not to do it. Appreciate your input.

I would absolutely, 100% use interface relays. Yes, it will *work* without - provided, as mendonsy mentioned, the grounding all checks out - but it's bad practice, and if something doesn't work (or stops working) it will be difficult to troubleshoot.

Throw in the cheapest relay you can find and you have a robust, reliable system.

+1 for interposing relays.

I try not to tie my power supply output low side to ground unless required by the hardware I am powering. I am not alone in my methods in my experience. It is not uncommon to run across a system where the negative terminal of the power supply is not at the same potential as ground and may vary.

I measured one a few days ago that was "floating" around the middle. 11 volts to one terminal and 13 to the other for a 24vdc power supply.

OkiePC said:

I try not to tie my power supply output low side to ground unless required by the hardware I am powering. I am not alone in my methods in my experience.

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Agreed, we always keep our 24v common isolated. Tried tying it to ground a few times and had nothing but trouble.