Can't say that I've seen an acorn clamp fail, but I have seen the other style -- the one with two bronze halves held with two screws -- fail.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.
Alex, welcome to the Forum.
It appears most of your questions have be answered, some with local amendments to the Code. You should ask your inspector if any apply, in your case.
Since the second rod is only needed if the first doesn't measure <25 ohms the NEC allows a second acorn to connect to the second rod. I quit measuring and just drive the second rod and thread through the first acorn, like others have mentioned.
Since you used a 10' rod you can stop driving it if 8' in in the ground. Depth of the GEC to the rods can be just below the surface or along a wall, but if subject to physical damage must be #4 CU.
Since the CW line from the street is corroded it's no longer considered a grounding electrode. However any metallic piping in your home should either be connected to the neutral in your panel or one of the GE's with at least #6CU.
This is probably the most important safety connection and is called "bonding".
The driven rods are most needed during a lightning storm. New homes don't drive rods but connect to the rebar in the slab (UFER) with #4 CU which must not be spliced with ordinary methods.
Lastly, Code now requires an "Inter-System Grounding" bus near your meter so Sat, cable, phone etc. can attach their ground wire. For under $20 you can attach it to your GEC and have a first class installation.
You say you're confused but seem to have a good grasp on the situation.
Good Luck from Columbiana, Alabama
Maurice Turgeon, Hidden Content
Agreed with Maurice. I'm a Ham radio nut and we ground towers against lightning with 3 rods, at least 8' in length, arranged in an 6' to 8' triangle, then connect with a single #4 conductor forming a loop around all rods with the 'loose end' going to the tower. The conductor can be buried slightly between rods if you wish, but not where the electrical connection is made. A little of overkill for the average home but the general method applies with multiple rod grounds- one conductor, no splices, and all tied together as well as possible.
@fencepost: I've seen one acorn clamp fail due to a flaw in the casting. As a matter of habit if I'm doing anything at the service entrance (or the panel if it's located there) I check the grounds physically and visibly. That one had a loose wire and when I tightened it one side snapped long before I had much torque on it. A close check showed a large void in the casting. I cannot fathom why it had apparently never been tightened, for if it had it would have failed on installation- not over 10 years later.