On 4/17/2020 1:29 PM, Ralph Mowery wrote:
In article , says...

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.




The ground rods are partly for lightning, but mainly for protection of
people. Those 2 ground rods you mention are really in parallel seperted
by the resistance of the wire between them, not series.

The ground rod or ground wire for the house is for when say you place
your hand on the washing machine and there is a short from the hot wire
to the frame of the washer. If you touch the washer and anyting else
that is grounded you will not get shocked. The skin of the body has
several thousand ohms of resistance, so the largest portion of the
current will go to the ground by way of the grounded conductor (usually
green or bare wire). The neutral wire should be connected to the ground
wire at the breaker/fuse box.


The ground rod also keeps the house ground from floating up or down with
the relative power used on the 2 hots coming in to the house. The fellow
across the street from me had lights that would get brighter or dimmer
as some appliance turned on or off. On my advise, they had the
electrician that re-did their wiring come check the ground rod
connections, which were not connected properly.