On Friday, April 17, 2020 at 4:04:58 PM UTC-4, Dean Hoffman wrote:
On 4/17/20 3:42 AM, micky wrote:
Do copper or copper-clad steel ground rods disappear with time?

After 37 years, does mine need replacing?

When I put in my first burglar alarm, 37 years ago, I put in a ground
rod to ground the system, and iiuc reduce the chance of lightening
damage. (Nonetheless, after about 20 years, when I was leaving for
work, there were wisps of smoke coming from the keypad/control usit, and
it never worked again. ;-) I have a new alarm now, grounded to the same
rod, but something told me the rod was gone. The top of it is still
there so maybe I dreamed it, but is it likely that the part above ground
is there but most of it below ground is gone, and needs replacing?

By the way, ground rods are primarily for lightning and other
large surges. They really don't do any practical good for short circuit
protection. The equipment grounding conductors are there for that.
Let's say the ground rod at your house and the one the the utility's
service both meet the 25 ohm or less standard. They're in series so the
two combined would have a resistance of 50 ohms. There won't be enough
current flow to trip a breaker to shutdown lethal current if there is a
short to metal in your house somewhere.
There's a calculator here if you want to see for yourself.
http://www.ohmslawcalculator.com/ohms-law-calculator
Enter 125 volts in the voltage box and 50 ohms in the resistance
box. The current flow through the two rods would be 2.5 amps, nowhere
nearly enough to trip a normally sized breaker or blow a normally sized
fuse.

I was going to say something along the lines of the alarm system should
be grounded to the service grounding electrode system. You're not supposed
to be driving separate ground rods for various systems or components.
But I suppose if it's at the opposite side of the house it might be tempting
to do so, not sure it buys you anything and it could make things worse.