grounding a sub panel at a separate building

[dia480]

do I carry the grounding/bonding electrode wire to the new subpanel in a seperate outbuilding or do I have to drive a new ground rod and then re-bond the whole thing like a new service?

[ June 06, 2003, 11:31 PM: Message edited by: dia480 ]

[don_resqcapt19]

A second building fed by a feeder always requires a grounding electrode system. If there are no conducting paths, other than the feeder circuit conductors, between the two buildings, you are permitted to install the feeder without an equipment grounding conductor and rebond the neutral at the second building. If there is any type of conducing path between the building, you must have an EGC and the neutral is not rebonded.
Don

[rasmithircgov.com]

What would be an example of the conducting paths. Would metal water piping be one of them if the water is fed from the other building and not a seperate supplied water service?

[jro]

If its a sub panel that is fed out of a main panel your grounding would be either your conduit or other recognized method Art.250.118, you don't treat it as a seperate service, all your main grounding should be at the first point of disconnect, at the sub-panel you would not bond the grounded conductor.

[iwire]

Originally posted by jro:
at the sub-panel you would not bond the grounded conductor.

Normally that would be true, but for a feed to a separate building you will have to bond the neutral to the ground if you chose not to run an equipment grounding conductor which is allowed if as Don pointed out there are no other metallic paths between buildings.

[iwire]

dia480

You have two ways to handle a feeder between two buildings.

With both methods you need a grounding electrode as required by 250.32

Method one

Run separate ungrounded, grounded and grounding conductors from one building to the other, do not bond the grounded conductor to the grounding conductor. Put in a grounding electrode at the second building and connect it to the grounding conductor.

Method two

If there are no other metallic paths between buildings (water pipes, coax cables, gas lines, whatever) you are allowed to run just the ungrounded and grounded conductors out the to second building.

In this case you must bond the grounded conductor to the panel enclosure and again install a grounding electrode connected to the grounded conductor.

Hope this helps, Bob

[ June 07, 2003, 12:51 PM: Message edited by: iwire ]

[pierre]

Hello dia480,
If this is a new installation that will or is being installed, I would 'advise' the installer to run the equipment grounding conductor (EGC) with the feeders (even though it is not required), and wire the same way as any 'subpanel'. Regardless of how you run the feeders, you are REQUIRED TO INSTALL A GROUNDING ELECTRODE SYSTEM as per 250.32(A). The purpose of the grounding electrode system at the 2nd building is for lightning protection. The grounding electrode conductor is connected to the grounding bus.

Good Luck,
Pierre

[don_resqcapt19]

Ras,
Water piping, gas piping, and communications circuits are all examples of metallic paths other than the feeder circuit conductors that would be conductive paths between the buildings.
Don

[tom baker]

Pierre, "I would 'advise' the installer to run the equipment grounding conductor (EGC) with the feeders (even though it is not required)," excellent advice. In Washington State, it is not allowed to reground the neutral at a separate building or structure (state code), effective May 23, 2003.

And a sepatate building does not always require a grounding electrode system. A building with a single branch circuit does not require a GES, and Art 210 states a multiwire branch circuit can be considered a single branch circuit, IE a 12-3 w/G to a garage does not require a GES.

[iwire]

If I was asked to do this I would not even think of not running a EGC, just out of habit from doing subpanels inside.

I do have a question for the theory guys though.

Wouldn't leaving the EGC behind and bonding at the second building be a good idea as that will create the shortest path for branch circuit fault clearing?

Say the buildings are 300' feet apart, by bonding at the second building you take 600' of conductor out of the circuit.

What is the down side of this method, other than the likelihood of a conductive path being established later?

Bob