(bold is mine)
Originally Posted by
Jon Randolph
Correct me if I am wrong, but I'm certain that the NEC will allow the other panel (sub, auxilliary, secondary, whatever you want to call it) to be grounded via a grounding rod, UFER ground or water piping if it meets the separation requirements from the main service panel ground.
"Will allow" I am assuming means 'instead of' being grounded back to the main grounding electrode system.
Only if there are no metallic paths which connect the two structures together. I believe that is what you are referring to (see bold below).
2005 NEC (bold is mine)
- 250.32 Building(s) or Structure(s) Supplied by Feeder(s) or Branch Circuits.
- - (A) Grounding Electrode. Building(s) or structure(s) are supplied by a 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.
- - - Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non–current-carrying parts of all equipment. For the purpose of this section, a multi-wire branch circuit shall be considered as a single branch circuit.
- - (B) Grounded Systems. For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either 250.32(B)(1) or (2).
- - - (1) Equipment Grounding Conductor. An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).
- - - (2)
Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of
- - - - (1) That required by 220.22
- - - - (2) That required by 250.122
- - (C) Ungrounded Systems. The grounding electrode(s) shall be connected to the building or structure disconnecting means.
- - (D) Disconnecting Means Located in Separate Building or Structure on the Same Premises. Where one or more disconnecting means supply one or more additional buildings or structures under single management, and where these disconnecting means are located remote from those buildings or structures in accordance with the provisions of 225.32, Exception Nos. 1 and 2, all of the following conditions shall be met:
- - - (1) The connection of the grounded conductor to the grounding electrode at a separate building or structure shall not be made.
- - - (2) An equipment grounding conductor for grounding any non–current-carrying equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conductors to a separate building or structure and bonded to existing grounding electrode(s) required in Part III of this article, or, where there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed where a separate building or structure is supplied by more than one branch circuit.
- - - (3) Bonding the equipment grounding conductor to the grounding electrode at a separate building or structure shall be made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building or structure.
- - (E) Grounding Electrode Conductor. The size of the grounding electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article.