I am upgrading from a 100AMP to 200AMP service. I need to run a grounding wire (bare CU #4AWG) from 2 grounding rods to the main electrical panel: 50 feet. I plan on running it underground. I wonder whether the minimum depth of 24" (18" if in PVC conduit) applies to grounding wire installed underground too or I can get away with less depth? If less, what would this depth be?

If this is residential, the minimum is 18", shown in Table 300.5, Minimum Cover Requirements, Zero to 600 Volts, Direct Burial of Cables or Conductors Column,One or Two Family row.

Why do you need to run this 50 feet?

Usually the ground rods are located much closer to the equipment being grounded. If this is to access the common grounding electrode, then fine I understand.

Hi tkrussell, thank you for the reply! Per my inspector I can connect the water pipe to the 2 grounding rods to the main panel. So instead of running the cable twice: once inside for 50 feet to the water pipe and another time outside to the 2 grounding rods, I decided to do this with one run.

Digging 18" deep within 1ft of the house will be OK. I did manage to place a couple of grounding rods close to the panel but I want to use them as grounding for a subpanel in the garage (2 additional 8ft rods are required for this in my city). I tried planting them around the garage at 45 degree angle but it is impossible because it is sitting on a large rock and I cannot dig a 2 1/2 ft trench either. So I managed to place 2 additional grounding rods at 45 degree angle and 6ft distance of each other in the area of the water pipe.

I wish I had bought an empty plot and started building a new house! Two years of renovations and there is still more to do :-)