Can you crimp onto the grounding electrode conductor in the main service panel?

Yes, if the crimp is made with a listed pressure connector and the right tool and die. Section 250.8(A) lists the permitted methods for connecting grounding and bonding conductors: listed pressure connectors, terminal bars, pressure connectors listed as grounding and bonding equipment, the exothermic welding process, machine screw type fasteners engaging at least two threads or secured with a nut, thread forming machine screws engaging at least two threads, connections that are part of a listed assembly, and other listed means. Sheet metal screws are specifically prohibited by 250.8(B).

Listed and identified matters more than the shape

A generic copper compression lug from the tool bag is not automatically acceptable on a grounding electrode conductor. The connector must be listed for the conductors being joined and, where used for grounding and bonding, listed as grounding and bonding equipment. Irreversible compression type connectors listed for the purpose, applied with the manufacturer specified die and tool, satisfy 250.8(A)(1). The die index number stamped in the finished crimp is what an inspector looks for.

Section 110.14(A) also applies. Connectors and terminals for conductors more finely stranded than Class B and Class C must be identified for the conductor class. And where copper and aluminum are joined, the connector must be identified for the combination and for the environment.

Splicing the grounding electrode conductor itself

Section 250.64(C) is the section that governs whether you may splice the GEC at all. The grounding electrode conductor must be installed in one continuous length without a splice or joint, except by irreversible compression type connectors listed as grounding and bonding equipment, by the exothermic welding process, where sections of busbars are connected together, or by bolted, riveted, or welded connections of structural metal frames.

Read that carefully. A wire nut, a split bolt, or a mechanical setscrew lug is not permitted to splice a GEC. An irreversible compression connector listed as grounding and bonding equipment is. That is exactly the crimp you are asking about, and it is legal when the connector carries the listing and the crimp is made with the matching die.

Termination at the electrode and at the enclosure

Section 250.70 requires the grounding electrode conductor to be connected to the electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means. The fitting must be listed for the materials of the electrode and the conductor, and where used on pipe or rod electrodes buried in earth or embedded in concrete, the connector must be listed for direct soil burial or concrete encasement. Not more than one conductor may be connected to the electrode by a single clamp unless the clamp is listed for multiple conductors.

Inside the panel, the GEC typically lands on the neutral or grounding busbar under its own terminal. Section 250.24(A)(4) permits the grounding electrode conductor to connect to the grounded service conductor at any accessible point from the load end of the overhead service conductors to and including the service disconnecting means.

Field takeaway

Crimping is acceptable when the connector is an irreversible compression type listed as grounding and bonding equipment and the crimp is made with the specified die. Mechanical setscrew splices on a GEC are not acceptable under 250.64(C). Sheet metal screws are never acceptable under 250.8(B).