The debates on this topic are endless and I won't try to settle them.
I will say that the US NEC requires that every building that has an
electrical supply that is more than a branch circuit must have a
grounding electrode system. There are no exceptions.
What you have done so far is great. Since you have an intercom between
the two buildings the code requires you to run an Equipment Grounding
Conductor (EGC) with the feeder conductors which you did. All that is
left to do is to connect the building disconnecting means to any
grounding electrodes at the garage / shop building or in the absence of
existing electrode you must install an electrode system. The point of
termination of the Grounding Electrode Conductor (GEC) to the
disconnecting means enclosure is usually done on the buss bar within the
enclosure that is bonded to the enclosure. In a three wire feeder the
bonded buss bar is the neutral buss. In a four wire feeder the bonded
buss bar is the EGC buss.
So Locate the existing electrodes or install one or more new ones and
connect them to the disconnecting means using an appropriately sized GEC.
This subject gets hashed around among inspectors quite a lot. It
breaks down to the definition of a branch circuit. The NEC Handbook
shows an illustration and a statement that a sub-panel requires an
electrode connected to the ground from the main panel. You'll never
be wrong to install the ground provided it is connected to the ground
from the main. An individual inspector may interpret in different
ways so sometimes it is easier to install it and be sure.
Might be a can of worms, without the ground rod, you could pass. Now
that you put one in you could fail till you put a second in, since now
you might not meet the 25 ohm requirement.
Just saying, if you don't follow what is in black and wihite, and can
interpet it to be anythign, what was the reasoning behind of writing
it down in black and white. The nec chould have have been one line,
Article1: Do what you feel is the max to ensure safety. End.
tom @ www.BookmarkAdmin.com
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