Add separate grounding to subpanel, split ground/neutral

I have a 100amp subpanel in my attached garage that is currently a 3-wire feed without separate ground. The neutral and ground are bonded on the same bars (which I understand was OK when this house was built, but no longer current code). I'd like to add a grounding wire and separate the neutral/ground in the subpanel. Feed from main panel to subpanel (shown coming up from bottom of picture) is run through 1-1/4 conduit, #4 wire, about 60 feet distance.

My plan is:
- run separate #8 copper ground wire alongside conduit (is an insulated black wire better than bare copper, or does it matter?), as I don't imagine it would be fun to pull another wire through existing conduit. Ground wires can be run separately, correct?
- add two ground bars to either side of the subpanel box to separate all existing grounds from the neutral bars
- add (redundant) ground wire to connect the two ground bars
- swap out 70 amp breaker for a 50 amp breaker (it's an electric range) and run separate ground wire to the receptacle so I can replace with proper 4-wire receptacle and plug. OK to retain existing #4 wire feed, which is overkill for a 50amp appliance circuit?

Criticisms/suggestions are welcome here. Seems pretty straightforward and well within my skill set, but would like confirmation before I apply for permit and start the work.

TIA for your advice!

First question - is the conduit that is coming from the main panel feeding this sub panel metal or PVC? I can't tell by the picture. If it is metal conduit the conduit acts like the ground in this case. But the neutral and ground should still be separate in the sub panel.

There are threaded holes already in the panel on each side where you would attached the ground bars. Move all grounds to those bars and leave the neutrals where they are.

afjes_2016 said:

First question - is the conduit that is coming from the main panel feeding this sub panel metal or PVC? I can't tell by the picture. If it is metal conduit the conduit acts like the ground in this case. But the neutral and ground should still be separate in the sub panel.

There are threaded holes already in the panel on each side where you would attached the ground bars. Move all grounds to those bars and leave the neutrals where they are.

Click to expand...

Conduit is PVC. Rest of plan look solid?

Sounds like a plan. Bare copper or sheathed, no matter (usually put some green tape on it to indicate ground if sheathed). Run it separate, no problem. Retain/reuse existing range wire, no problem.