I am putting in a generator with an automatic transfer switch (ATS). The ATS will go between the meter and what is currently the main panel. The ATS has a service disconnect breaker and will become the "main" panel, and what is currently the main will become a "sub" or distribution center. I will pose my question referring to the two boxes as the ATS and the "sub," respectively. Currently there is a grounding cable from the "sub" running outside to a pair of grounding rods in the earth, and a grounding cable completely inside that runs to the copper cold water pipe where it comes into the house. Currently the neutral bus and the ground bus in the sub are bonded, but I will be removing that connection when the ATS gets installed; the neutral will be grounded in the ATS.

Now, the question I have is, will I have to remove the grounds in the sub that go to the water pipe and the ground rods and place them into the ATS (which will be problematic, since they will not reach as is) or will it be sufficient to just run a ground wire from the ATS to the ground bus in the sub?

Follow-up question, if I need to move the ground wires out of the sub and into the ATS, can I splice the ground wires? They are both what looks to me like bare, stranded #6 copper, but I am not totally sure about the size.

The neutral and grounding can only be electrically connected, "bonded", at the enclosure that contains the Main Breaker, or before the main. After the Main, the neutral must be insulated and isolated from equipment grounding.

Grounding electrode conductors must be continuous, or if spliced , must be irreversible connection, such as a compression crimp connector.

You can buy compression connectors at electrical distributors, and some loan or rent out the crimp tool.

Therefore, you cannot use the screws in the ground bar in the "sub" to splice the grounding electrode conductor.

The grounding electrode conductor is probably #6 copper,but you need to be sure. Cut off a sample and bring it with you when you buy more wire and the crimp connectors.

Good time to check the connections to ground rods and water pipe.

Thanks. That was what I thought, but I was hoping a ground jumper would work. I appreciate the info about the compression connectors. That will be much easier (and cheaper) than re-threading 50 feet of #6 copper just to go another 4 feet.