This was written in response to a Graze-L discussion.
-Currently, I run my ground wire to the ground on my electrical panel which in turn grounds to the barn water supply line and a single 8 foot grounding rod. Is this an improper hook up and why (it seems to work, last time I touched it)?
If there is very little load from the fence or if the charger is low power, the grounding system does not have to move much current to adequately complete the circuit on the fence. It would normally be a waste of time to install more than a foot of ground rod for a portable battery fence charger. All manufacturers seem to strongly discourage grounding the fence circuit (ground terminal of the charger) to the utility grounding system. Where milking equipment, feeding or watering systems may be in any way connected to the fence circuit of the charger, the risk of reduced profit is great - especially with the higher powered chargers.
Contrary to the manufacturers, I recommend keeping the ground field away from the charger if it is near the milking parlor. Four years ago we had a problem with stray voltage in our 12-unit milking parlor. I ran a heavy copper ground wire from the ground rod the power company had put under their transformer to a 30 inch galvanized culvert under our road. As I shoveled the wire under the sod of our lawn, I kept getting a pulsing shock as I pushed the wire down under the grass. After I attached it to the culvert, the stray voltage was mostly gone. Our charger was independently grounded but the rods were near the parlor.
If there is already a non-electrified wire on the fence, bring that wire on to the ground terminal. Put in ground rods in damp areas along the fence and attach (use a tap sleeve or bolt) to the non-electrified wire. If there are steel culverts under a road along the fence, you have a great ground. Drill it and run a wire to it.
About 15 years ago when I was contract fencing 7 miles of electric deer fence, I put in 10 eight foot ground rods (in a wet area) for a 21 joule PEL 300. It still had hundreds of volts showing on the voltmeter.
If you, your neighbors and your power company are not concerned with stray voltage, you will likely have fewer lightning problems by bonding the charger ground to the utility ground. Lightning often hits the power line and has to go through the charger to get to the charger ground. A surge suppressor between the two ground fields would probably be the best way to go.