Grounding Old Main Panel, Locating Grounding Rods

[tortuga]

We have replaced a subpanel in a very old electrical system that has no ground to the main panel and no grounding rod(s). Long story short -- we are not now upgrading the main panel and have no convenient location to install the ground rods at that location.

I'm thinking that I run a new ground wire to the main panel from our new subpanel, connect this to the existing neutral bar there, but run the ground rods from the subpanel location. Assuming that all the grounds are connected but still floating (separate from the neutrals) at the subpanel location, is there any problem with this setup?

Should of taken a pic of the existing main panel ... its quite something ... I'll try and get some Monday

Thanks

What is the wiring method and type and size of conductors between the subpanel and the service panel?

 

[Benhear]

the main is a 55A breaker with 6/3 sheathed cable (no ground) running to the sub-panel -- this cable runs in walls and ceiling and is not readily accessible

 

[charlie b]

. . . but I don't see the rationale. Is there a technical reason for why the ground must run with the conductors on feeders (but not necessarily on branches)?

I believe it is to enable making non-grounded receptacles safer, without having to open up walls or doing some other drastic installation task. It doesn't apply to all branch circuits, but rather only when replacing receptacles or extending branch circuits, when neither presently has an EGC. The general requirement is that all circuit conductors share a conduit (or a set of parallel conduits).