Common ground between ATX power supplies

[bitman]

On my bench power supply I have common ground. I even connect one bench supply + to another's - to get multiple voltages for the same project. It works, I know how and it's very helpful. 

But I'm in the need to temporary add a second ATX power supply to a computer while I add more drives to migrate off the existing ones. The current supply is too small to handle this, so my plan is to just power the new drives temporarily from a second supply, move the data, remove the old ones and go back to just one PSU.  But I need the two supplies to have common ground as the drives connect to the same motherboard.  Is there anything on a standard ATX power supply that would prevent this from happening? Ie. if I connect the ground lines from one to the other, will this cause some safety in the ATX supply to go "nope - cannot do that"?

Perhaps the better question is: How can I tell without risking blowing both supplies up in the process?

[msat]

It should work "in theory". I wouldn't rely on the grounds being shared strictly through the IEC power cables, though. Instead, find a better way to bond the PSUs together. Then check the resistance through the ground terminals on drive power connectors between the supplies, to ensure there's no unusually high resistance. But I wouldn't try it on my word alone because I've never tried it myself.

[golden_labels]

For short tests: I was doing that many times in my life with no issues. As a permanent solution: I would be careful, but this is not a “will not work”.

For power hungry components the current goes through the same plug both directions, so each of them is always powered from a single PSU. The ground connection is there mostly to provide common reference for signals. The main concern are motherboards with multiple connectors and PCI-E cards, as they share power lines. Be sure to connect them all to a single PSU.

[m k]

I've temporarily used second PSU by just putting it on the floor of a standing metal case.

It should be totally ok if you bolt metal cases together, with or without the decent wire.