can two sub-panels share one ground?

Hi, I have a pretty simple question with probably an overly complicated backstory. But here it is:

Inside the pantry of my kitchen are two sub-panels, both with 2 20amp breakers in them. The sub-panel on the right has all new wiring that is grounded back to the main. We'll call this Sub-panel(N) for new. The sub-panel on the left is fed off old wire (house built 1949, but who knows how old this wiring is?), and only has a neutral and a hot. I'll call that Sub-panel(O) for old.

What I would like to do is connect new romex (14/2) to one of the breakers on Sub-panel(O) but need it grounded. Can I run a ground wire between Sub-panel(N) and Sub-panel(O)?**

If not, can I run a ground from a plumbing fixture outside the wall to the box for ground wire?

If both are acceptable, is there a reason I would want to do one over the other?

Thanks!
*House is in Phoenix AZ and is built out of slump-block with old wiring run through the block.

**I'm going to be adding foam insulation in the living room, so may as well take the opportunity to update the wiring.

 

Welcome to the forums!

How much clear working space is there in front of each of these panels, from the wall out, from side-to-side, and from the floor to the ceiling?

Yes. Will doing that provide the old subpanel with a code-compliant equipment grounding conductor? Unfortunately, no. The EGC associated with a circuit must either be pulled with that circuit or pulled on its own from the ground bus in the panel where the overcurrent protection device - the fuse or circuit breaker - for that circuit is mounted.

No.

How is the wiring for the newer subpanel run? What size are the conductors in that run? What size and type is the breaker protecting that run?

 

Thanks Nashkat1!

Bad news is always best delivered straight. Is there any way to run a ground to this panel, or should I just leave the electric as it is?

I get the ground bus in the panel to the circuit, but what does it mean to be "pulled with that circuit"? I guess from a non-professional P.O.V., I could just pull both boxes out and put a larger sub-panel in which would hold all 4 breakers. In that case all 4 would be sharing the ground. The two panels are right next to eachother. 1.5" between them side to side; the pantry is 30" deep' panels about 36" off the ground.

(Sub-panel(N) has what looks to be 8 wire from a 40 amp through conduit to the panel and Sub-panel(O) has what appears to be the same size wire but only a 30 amp breaker at the main.)

 

With conduit you can feed any subpanel you want. You need to have a space 36" deep and 30" wide, floor-to-ceiling, in front of the panel. What would you like to feed from this subpanel, total?