Sizing machine ground for safety on 24VDC circuit

[frankmurph]

All. I tried this in the NEC forum but got no bites. I'm looking for help sizing a ground wire (to earth) from a ground bar on a DC circuit. We have designed a piece of equipment with (3) 120 in/24VDC out power supplies. The PS 24VDC distributed commons are grounded (the 24VDC returns are brought to the AC ground at the PS secondary). The AC side is all safely grounded of course. Each of the power supply 24V 'hots' are fused at 20 amps DC. We have bonded all of the 24VDC devices to a common Ground Bar in the machine. We want to run a single conductor (non current carrying grn/yel) safety back to ground, but there is disagreement whether this conductor must be sized for a full 60 Amp potential (entire DC side) or can we just run a wire for 20Amp potential (a single failure would draw no more). Any help is appreciated.

Frank

 

[Smart $]

If your DC output commons are already grounded to the AC supply circuit EGC, that's all that is all that is required and necessary.

 

[petersonra]

The egc for the dc starts where the dc starts so no special sizing of egc back to ac source is required.

Do any of these dc supplies feed anything outside the control panel?