Odd GES

2037 Views 16 Replies 6 Participants Last post by AllanJ, Dec 12, 2012

Stubbie

Discussion Starter · Dec 10, 2012 (Edited)

Is this code compliant

I was asked to come down to farm home to bid the electrical on job for a fountain install to a small lake.

I ran into this for the GES while looking at equipment and panels. The 200 amp service equipment is mounted on the farm pole .. a 3 wire feeder is ran up the pole where they split it one 3 wire feeder to the dwelling and one 3 wire feeder to the barn. The feeder to the newer shop is fed from the barn panel and is a 4 wire feeder .. neutral and ground separated at the shop panel. The red lines are the feeders.
Probably barn and home are 50 years old so the 3 wire feeders would be compliant when they were installed.

However the barn and new shop are sharing the ground rods with the service equipment. I assume this is because the property is all rock and driving the ground rods in any compliant fashion for each building would be quite an effort.

Is this compliant ?

I have the answer from the county building department but I'm not sure I agree. Doesn't really matter but this is one of those things that I feel is a great learning tool when discussed on a forum. So I'm throwing it out there to see what your opinions are ...

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k_buz

· #2 · Dec 10, 2012

If there is a GEC going from the shop to rods, then I would say it is compliant. I don't rember anything in the NEC stating that you cannot "share" rods or where the rods need to be located.

Stubbie

Discussion Starter · #3 · Dec 10, 2012

Rather than keep every body guessing . Your answer is correct according to county. Would like to see if any one can give an argument to the contrary ..

I'll post some of my thoughts later today or tomorrow.

Jim Port

· #4 · Dec 10, 2012

Interesting take on the electrodes for outbuildings.

mpoulton

· #5 · Dec 10, 2012

That's a very interesting question. I would say the county is correct, but that this is the very definition of a loophole: the code as-written allows an installation that is clearly against the intent of the drafters. Outbuildings require grounding electrodes... but those grounding electrodes don't have to be right next to the building, and other buildings could use them too! Thus, outbuildings don't really require grounding electrodes if you run a GEC with the feeder.

stickboy1375

· #6 · Dec 11, 2012

I just did a job where they built a garage about 20' from the original structure, I installed a conduit between the structures, I drove 3 ground rods; one at the house structure, one in the middle of the trench, one at the garage... the meter at the house contained that structures disconnect, so I ran #6 cu. from the meter to the first ground rod, to the middle ground rod, to the garage ground rod, then to the garage disconnect. I thought it was nice.

stickboy1375

· #7 · Dec 11, 2012

mpoulton said:
Thus, outbuildings don't really require grounding electrodes if you run a GEC with the feeder.

I've never seen that nor interoperated that from the NEC. I dont believe that is correct. Nor would want that for the simple reason of bringing lightning into another structure.

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mpoulton

· #8 · Dec 11, 2012

stickboy1375 said:
I've never seen that nor interoperated that from the NEC. I dont believe that is correct. Nor would want that for the simple reason of bringing lightning into another structure.

It's not the intent and it is a problem, but I don't know of a reason it wouldn't be code compliant. It's pretty much exactly the situation the OP is describing: grounding electrodes near the service that are also being used as the GES for outbuildings, with separate GECs.

Stubbie

Discussion Starter · #9 · Dec 11, 2012 (Edited)

Ok here is my problem and use the below diagram or the one earlier to reference. County is on 2008 NEC. I've got a 3 wire feeder to a barn panel fed from the service equipment on a 'farm pole' . From that panel I have a 4 wire feeder to a shop. 250.32 says that no other conductive paths can exist between buildings in order for a three wire feeder to be compliant. If I share the grounding electrode (rod) of the service equipment with the two buildings I now have a conductive path(s) of very low impedance/resistance between all three buildings. In my opinion that makes the 3 wire feeder non compliant , and maybe even non compliant at the time of install.

Adding to this visualize the neutral of the 3 wire feeder from service equipment to the barn panel becoming open. I now have all neutral current from the barn and shop using the gec of the barn to the common rod to return to the transformner via the gec from that same rod that is connected to the service equipment.

My opinion is this violates 250.32 (B) no other conductive paths allowed for 3 wire feeders.

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stickboy1375

· #10 · Dec 11, 2012

At the farm pole, is OCP even required, why not run service entrance conductors instead of feeders?

AllanJ

· #11 · Dec 11, 2012 (Edited)

If a building has a panel (or subpanel, or more than one) then it needs a grounding electrode system (e.g. two ground rods) connected to the first panel.

Outbuildings with a plain feed, which in turn has to be 20 amps or less (ordinary lights and receptacles may not go on a circuit of more than 20 amps) don't need a GES.

stickboy1375 said:
At the farm pole, is OCP even required, why not run service entrance conductors instead of feeders?

When there is no overcurrent protection at the farm pole then the service conductor rules apply e.g. where the panel with OCP in the building must be within X feet of where the feed cable enters the building.

stubie said:
... If I share the grounding electrode (rod) of the service equipment with the two buildings I now have a conductive path(s) of very low impedance/resistance between all three buildings. In my opinion that makes the 3 wire feeder non compliant , and maybe even non compliant at the time of install.

Adding to this visualize the neutral of the 3 wire feeder from service equipment to the barn panel becoming open. I now have all neutral current from the barn and shop using the gec of the barn to the common rod to return to the transformner via the gec from that same rod that is connected to the service equipment.

My opinion is this violates 250.32 (B) no other conductive paths allowed for 3 wire feeders.

Note that a water pipe or cable TV coax running between the two buildings also counts as a conductive path and will render the 3 wire feed noncompliant.

(OT) Also, if a neutral anywhere becomes open, all bets are off. With a 3 wire feed between buildings, should the neutral become open, outbuilding return current uses the grounding electrode conductor with or without a shared ground rod only because neutral and ground are correctly bonded at the first outbuilding disconnect. With a 4 wire feed between buildings, neutral and ground are correctly not bonded anywhere in the outbuilding so return current does not use the GEC.

.

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stickboy1375

· #12 · Dec 11, 2012

AllanJ said:
If a building has a panel (or subpanel, or more than one) then it needs a grounding electrode system (e.g. two ground rods) connected to the first panel.

(Outbuildings with a plain feed, which in turn has to be 20 amps or less, don't need a GES.)
.

Was this directed at a comment or just general knowledge being given out?

stickboy1375

· #13 · Dec 11, 2012

AllanJ said:
If a building has a panel (or subpanel, or more than one) then it needs a grounding electrode system (e.g. two ground rods) connected to the first panel. Disconnect, not always a panel.

(Outbuildings with a plain feed, which in turn has to be 20 amps or less, don't need a GES.)
.

Where did the 20 amps come from? As long as it's a single branch circuit or MWBC and contains an equipment grounding conductor, I don't need a grounding electrode system.

Stubbie

Discussion Starter · #14 · Dec 11, 2012 (Edited)

stickboy1375 said:
At the farm pole, is OCP even required, why not run service entrance conductors instead of feeders?

You can do that and many times you will see a utility isolation device way up on the pole and a long rod that comes down the pole that you use to open the service conductors via a enclosure similar to an unfused disconnect. The pole is called the farm distribution point and most of the requirements when those come into play is in the article covering agricultural buildings in the NEC.

Getting back to what I am making a point of.... even if I do not have an open neutral in the feeder to the barn. Half my neutral current is using the gec's from the service equipment and the barn to return to the transformer because both panels (SE and barn panel) are bonded to the grounded conductor at each panel and they are using a common rod electrode.. If I take a meter I'm going to see substantial current flow on those gec's under normal operation.

I have a parallel path that the neutral current is going to split on.

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stickboy1375

· #15 · Dec 11, 2012

stubie said:
You can do that and many times you will see a utility isolation device way up on the pole and a long rod that comes down the pole that you use to open the service conductors via a enclosure similar to an unfused disconnect. The pole is called the farm distribution point and most of the requirements when those come into play is in the article covering agricultural buildings in the NEC.

Getting back to what I am making a point of.... even if I do not have an open neutral in the feeder to the barn. Half my neutral current is using the gec's from the service equipment and the barn to return to the transformer because both panels (SE and barn panel) are bonded to the grounded conductor at each panel and they are using a common rod electrode.. If I take a meter I'm going to see substantial current flow on those gec's under normal operation.

I have a parallel path that the neutral current is going to split on.

I understand your parallel neutral dilemma, what they did never should have occurred. If you ever end up with a open neutral, someone could get hurt or worse.

Stubbie

Discussion Starter · #16 · Dec 12, 2012

stickboy1375 said:
I understand your parallel neutral dilemma, what they did never should have occurred. If you ever end up with a open neutral, someone could get hurt or worse.

Well to end this I'm not doing the job .. I've decided to walk away. I need 125 feet of trench thru a solid rock shelf to get to the pump location. Im not even sure if I can find a trench contractor that would fool with it. I don't need the head ache and jobs like this seem to always turn out to be a mistake if you take them on. Besides I'm retired I need the easy stuff ...

I briefly told the owner about the issue we have been discussing but I didn't get his attentiuon I don't think. Maybe he will call the county out to look ..hard to say. Sometimes you just have to move on.

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AllanJ

· #17 · Dec 12, 2012 (Edited)

stickboy1375 said:
Where did the 20 amps come from?

(correction) If it is a "special purpose" circuit, namely not having any "standard" light fixtures or 15 amp or 20 amp receptacles, then it can be more than 20 amps, and without a subpanel and grounding electrode system where it gets to the outbuilding.

Note that the outbuilding may receive only one feed. If you run a special purpose circuit of more than 20 amps, say, for some heavy machinery, then you may not also run a general purpose circuit for lights, etc. This is why you need the subpanel and GES, receiving the single circuit (usually a 120/240 volt circuit aka multiwire branch circuit) with adequate ampacity for both the special purpose loads and general purpose loads.

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