Bonding remote building feeder ges to service ges

[Don Brown]

Many older remote building feeders have been installed using 3 conductors without a ges at the remote building. No continuous metal exist between buildings. Just direct burial or pvc between the buildings. I usually get to inspect the installation after a lightning event.

A grounding path to a ges is needed so a ground rod and an egc can be installed.

Now the grounded and grounding conductors need to be separated to an isolated neutral bar and a grounding bar.

Then a single ges is required to avoid potential difference between the remote building ges and the service ges, so...

(1) Does adding the grounding conductor to the feeder circuit to the remote building provide bonding of the remote building ges to the service building ges thus forming a single ges?

(2) Does a bonding conductor between a remote building ges and the service building ges allow a 3 conductor feeder circuit with only a feeder neutral?

(3) Is a bonding conductor connecting the remote ges and the service ges required "and, also" a fourth feeder conductor for the circuit grounding conductor?

I have read both the NEC 2005 and 2008 concerning this issue and find it very difficult to answer those 3 questions...

 

[frizbeedog]

(1) Does adding the grounding conductor to the feeder circuit to the remote building provide bonding of the remote building ges to the service building ges thus forming a single ges?

...

The equipment grounding conductor does not qualify as a grounding electrode conductor.

...and each building or structure served has it's own grounding electrode system.

See 250.50

and.

Grounding Electrode Conductor definition in Art. 100.

 

[Don Brown]

Perhaps I should have asked that question a different way.

If a ground rod and a gec are installed at the remote building "and" a grounding conductor is added to the feeder circuit, does the grounding conductor in the feeder circuit effectively bond the grounding rod at the remote building to the grounding rod at the service building?

Or is another conductor required to bond the remote building ground rod to the service building ground rod to eliminate potential differences between the 2 ground rods?

 

[JohnJ0906]

Perhaps I should have asked that question a different way.

If a ground rod and a gec are installed at the remote building "and" a grounding conductor is added to the feeder circuit, does the grounding conductor in the feeder circuit effectively bond the grounding rod at the remote building to the grounding rod at the service building?

Or is another conductor required to bond the remote building ground rod to the service building ground rod to eliminate potential differences between the 2 ground rods?

There is no requirement to bond GESes of seperate buildings.

Is there a reason that you want to bond them?

 

[Don Brown]

The reason is to achieve a single ges so that the ground potential rise during a lightning event doesn't cause a potential difference between the 2 ges. If all electrodes are bonded together then the ground potential rise at all electrodes should be the same.

My question is "does the grounding conductor of the feeder circuit effectively bond the 2 ges so that the 2 electrode systems rise at the same rate?"

Reference exhibits 250.39 and 250.40. In 250.39 surge energy can flow through the equipment because of a potential difference. In 250.40 the potential difference is eliminated by the bonding of the 2 ground points.

So in the remote building and the service building ges with a grounding conductor in the feeder circuit, are the 2 ges bonded? Will the 2 ges rise and fall at the same rate?

 

[benaround]

Don,

Yes, the EGC of the feeder to the out building will 'bond' both buildings. Are they at the

same potential difference ? I doubt it.

 

[don_resqcapt19]

I don't think it is even possible to keep them both at the same potential, but the EGC will limit the potential between the two buildings. I don't really understand why the ground potential at the two buildings needs to remain the same, unless you have some type of communications circuit running between the buildings that is referenced to ground at both ends.

 

[tryinghard]

The reason is to achieve a single ges so that the ground potential rise during a lightning event doesn't cause a potential difference between the 2 ges. If all electrodes are bonded together then the ground potential rise at all electrodes should be the same. My question is "does the grounding conductor of the feeder circuit effectively bond the 2 ges so that the 2 electrode systems rise at the same rate?"

Don,

Grounding is required as per 250.4(A)(1) and lightning is the most likely reason for its need. Grounding at separate buildings/structures is required as per 250.32 and if your on 2008 you must feed these with an equipment ground separate (not common with) the neutral, in new construction there?s really no exception. The reason for this is to curtail parallel returning current and contain it on the insulated grounded conductor only.

The EGC does bond the GES? but I don?t believe it is intended to keep zero potential for lightning. Lightning is a dc arc flash nearly instantaneous, good grounds will effectively route it.

Reference exhibits 250.39 and 250.40. In 250.39

These are not in the NEC?

 

[Don Brown]

Thanks for all the feedback.

I am involved in communications between buildings. I have seen a lot of damage from lightning. I understood about separating the neutrals and grounds at a remote panel to avoid parallel paths for a neutral return to the service.

What I could not determine was the bonding of the 2 ges. I now understand that the egc of the feeder circuit bonds the 2 ges. And if a separate and larger grounding conductor is also installed to bond the 2 ges that is ok because it is not a parallel neutral but a parallel ground. Maybe the second grounding conductor is not required but seems it can't hurt...

I recommend fiber optics or wireless over copper between buildings but due to the cost of fiber and wireless, one needs all the facts before making a case to switch.