Grounding in second structures

[mtdimp]

When installing a subpanel in a second structure, should the electrician install a separate ground or connect it to the primary panel.

 

[iwire]

Re: Grounding in second structures

Short answer look at 250.32 Two or More Buildings or Structures Supplied from a Common Service.

Long answer read on.

There are two code compliant ways to do this.

1)You can always run the ungrounded, grounded and grounding conductors, use a panel with an isolated neutral bar at the second building and connect a grounding electrode to the grounding bar in this new panel.

250.32(B)(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) If there are no metallic paths between the two buildings you can run just the ungrounded and grounded conductors from one building to the other, bond the this grounded conductor at the panel and connect a grounding electrode to this new panel.

250.32(B)(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 common ac service, 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

In both cases you do need to connect a grounding electrode to this new panel.

250.32(A) Grounding Electrode.
Where two or more buildings or structures are supplied from a common ac service by a feeder(s) or branch circuit(s), the grounding electrode(s) required in Part III of this article at each building or structure shall be connected in the manner specified in 250.32(B) or (C). Where there are no existing grounding electrodes, the grounding electrode(s) required in Part III of this article shall be installed.

Exception: A grounding electrode at separate buildings or structures shall not be required where only one 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.

That's the code now just my opinion, run separate conductors for the Neutral and grounding.

Hard to really know if there are now or will be later "no continuous metallic paths bonded to the grounding system in both buildings or structures involved"

This metallic path could be the water, gas, phone, cable services etc.

[ October 31, 2003, 06:20 AM: Message edited by: iwire ]

 

[pierre]

Re: Grounding in second structures

Even if every electrician on earth understood the requirements for this installation, plumbers, data people and others do not. So one may choose not to use an EGC in the installation and later a plumber comes to install a water line to the building and we have a problem. I say this installation should ALWAYS have an EGC, even if the NEC says it is permitted not to if all of the conditions are met.Just my opinion!

Because this is a safety issue, the code should IMO take into consideration that this type of installation can be affected by other trades and they are not trained in the NEC, so how are they to know it is an unsafe installation?

Pierre

[ October 31, 2003, 07:38 AM: Message edited by: pierre ]

 

[mtdimp]

Re: Grounding in second structures

Thanks Guys,