On Tue,7/26/2016 10:30 PM, Christopher Brown wrote:
The NEC has strict standards for the Grounding Electrode System, and
exactly where and when neutral (ground_ed_ conductor) can be bonded to
ground (ground_ing_ conductor).
It does not limit the number of rods/other that can be used in addition
to the minimums.
Also, additional ground rods/other can be added basically_anywhere_
bonded to a ground lead or equipment chassis. These are simply NOT part
of the grounding electrode system and cannot substitute for any other
grounding requirement.
Correct on all counts.
If you dig a bit there is language about supplemental and supplementary
grounding electrodes. I forget which is which, but one is bonded to the
GES via #6 or larger bonding run, the other is not.
NEC places very little importance on the quality of the connection to
earth. It calls for some maximum value of resistance to earth (25
ohms?), and if a single rod does not provide it, a second rod must be
driven. That's ALL it says! What matters, and what is says a LOT about,
is BONDING -- that is, how grounded equipment and earth electrodes and
parts of the system are connected together.
They are both allowed, but_do not do not do not_ replace/substitute for
any required grounding/bonding...You can drive a rod and bond it to the
chassis of a AC powered machine, but this does not in any way remove the
requirement of bonding the chassis to the AC grounding conductor in the
AC feed.
Exactly right. The equipment ground (the green wire) MUST follow the
path of the phase and neutral conductors and be bonded to exposed metal
of equipment. The fundamental principle here is that the primary purpose
of the equipment ground (the green wire) is to blow the fuse or breaker
if something in the equipment fails and causes the equipment chassis to
be hot. In other words, it's electrical safety. Using a separate ground
conductor for this function, even if it is bonded to other grounds, is
prohibited because the return path is highly inductive, making the
fuse/breaker blow more slowly.
And using only a driven rod at the equipment with NO ground conductor
from the panel to the load is CRAZY unsafe, because the earth is
basically a big resistor, and doesn't conduct enough current to blow the
breaker. In my life in pro audio, we ran into dumbos who insisted on a
separate "clean audio ground," not connected to the building ground.
Mondo unsafe, for the reasons stated, and it does nothing to make audio
systems cleaner.
73, Jim K9YC
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