TK - Stan - Wash - KISS,

For the purpose of discussion: :)

A subpanel located in the same residence as the main panel uses the main panel's Ground system. Separate Grounding rods and EGC are not needed for the subpanel

For a remote building, a sub panel must have its own independent grounding system that is not connected to the Main Panel grounding.
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Almost:

Neutral to ground rod bonding occurs at the utility disconnect.

If disconnect is separate/remote such as at the meter base, all panels are treated as sub-panels.

If a sub is installed in a detached structure, both a ground to the main panel and a ground rod is installed, otherwise just a ground.

At the sub ground and neutral are isolated.

Why a ground rod for a detached structure?

1. To handle lightning strikes, otherwise it could travel along the feeder.
2. Surface ground potential can be different during storms. Distance can increase this difference. That bond can help equalize the earth's potential.

Quote:

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Originally Posted by donf

For a remote building, a sub panel must have its own independent grounding system that is not connected to the Main Panel grounding.

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Not so Don. There is no wording making an independent rod mandatory.



Here is the NEC text on this:

250.32 Buildings or Structures Supplied by Feeder(s) or Branch Circuit(s)
(A) Grounding Electrode Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with 250.50. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.