Is this Grounding Diagram correct?

charlie b

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Yes and no. Per 250.66(A), if you are only connecting to rods, pipes, or plates, and there is not a different type of electrode further downstream, then #6 copper is sufficient. That is the "yes" part. The "no" part is that the grounding electrode conductors need to be attached to the neutral bus, not the equipment ground bus. I know that they are bonded together, but right is right nonetheless.
 

mbrooke

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Yes and no. Per 250.66(A), if you are only connecting to rods, pipes, or plates, and there is not a different type of electrode further downstream, then #6 copper is sufficient. That is the "yes" part. The "no" part is that the grounding electrode conductors need to be attached to the neutral bus, not the equipment ground bus. I know that they are bonded together, but right is right nonetheless.
Thanks :)

But- help my understand why code says its ok:

1) The gas pipe is technically a grounding electrode as metal gas mains can run the entire town.

2) A 600amp circuit could energize the fire sprinkler pipping as much as a 200amp circuit.
 

charlie b

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But- help my understand why code says its ok:
1) The gas pipe is technically a grounding electrode as metal gas mains can run the entire town.
2) A 600amp circuit could energize the fire sprinkler piping as much as a 200amp circuit.
Why does the code say that if you run a GEC to structural steel, you size it on the basis of the service conductor size, but if you run one to a ground rod, you need not go bigger than #6 no matter how large the service conductor are? I have no idea.

Regarding item 1, I can't answer for K8MHZ's comment. It may be a plumbing code, but I don't think it is in the NEC. However, a water pipe can serve as an electrode if it has at least 10 feet in contact with dirt. How long it is after that, even if it runs all through the town, matters not in the least.

Regarding item 2, if any circuit comes into contact with a piping system that is serving as a grounding electrode, that electrode will utterly disregard the event. By that I mean that dirt will not become part of the fault-clearing path. Rather, the bonding conductors that essentially tie all metal throughout the building, metal that has the possibility of becoming energized, back to the main panel's grounding bus, and from there to the neutral bus via the main bonding jumper, will establish a low-impedance circuit. This will result in a high current that will terminate the event by tripping the main, feeder, or branch circuit breaker, depending on where the fault took place.

It appears to me that you are confusing the grounding electrode system with the fault clearing duties of the equipment grounding conductors and bonding conductors.
 

mbrooke

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Why does the code say that if you run a GEC to structural steel, you size it on the basis of the service conductor size, but if you run one to a ground rod, you need not go bigger than #6 no matter how large the service conductor are? I have no idea.
A single (or even multiple) ground rod will not have an ultra low resistance even in the best soil, where as structural steal can be the equivalent of 10,000 ground rods in parallel. Also I would think structural steal could in theory become energized by the largest circuit in the building where as a ground rod is not likely.


Regarding item 1, I can't answer for K8MHZ's comment. It may be a plumbing code, but I don't think it is in the NEC. However, a water pipe can serve as an electrode if it has at least 10 feet in contact with dirt. How long it is after that, even if it runs all through the town, matters not in the least.

Regarding item 2, if any circuit comes into contact with a piping system that is serving as a grounding electrode, that electrode will utterly disregard the event. By that I mean that dirt will not become part of the fault-clearing path. Rather, the bonding conductors that essentially tie all metal throughout the building, metal that has the possibility of becoming energized, back to the main panel's grounding bus, and from there to the neutral bus via the main bonding jumper, will establish a low-impedance circuit. This will result in a high current that will terminate the event by tripping the main, feeder, or branch circuit breaker, depending on where the fault took place.

It appears to me that you are confusing the grounding electrode system with the fault clearing duties of the equipment grounding conductors and bonding conductors.
Of course, which is why you would want the gas, fire, ect bonding conductors sized to 250.122. Do you want a 600amp circuit being cleared via #6?

It just make no sense to me that structural steel and the water main need 3/0 but not the rest of the piping.
 

mbrooke

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It's in NFPA13 and I believe somewhere in chapter 10 it specifically prohibits using Fire Sprinklers for GE's

See 250.104(B)

Roger




As I'm reading it, #6 would be a code violation?


(B) Other Metal Piping. If installed in or attached to a building
or structure, a metal piping system(s), including gas piping,
that is likely to become energized shall be bonded to any of the
following:
(1) Equipment grounding conductor for the circuit that is
likely to energize the piping system
(2) Service equipment enclosure
(3) Grounded conductor at the service
(4) Grounding electrode conductor, if of sufficient size
(5) One or more grounding electrodes used, if the grounding
electrode conductor or bonding jumper to the
grounding electrode is of sufficient size
The bonding conductor(s) or jumper(s) shall be sized in
accordance with Table 250.122, and equipment grounding
conductors shall be sized in accordance with Table 250.122
using the rating of the circuit that is likely to energize the
piping system(s). The points of attachment of the bonding
jumper(s) shall be accessible.
Informational Note No. 1: Bonding all piping and metal air
ducts within the premises will provide additional safety.
Informational Note No. 2: Additional information for gas piping
systems can be found in Section 7.13 of NFPA 54 -2015, National
Fuel Gas Code.
 

charlie b

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As I'm reading it, #6 would be a code violation?
I think not. Your citation is related to bonding jumpers. The original question, and the sketch, are related to grounding electrode conductors. See my code citation in post #2.
 

roger

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As I'm reading it, #6 would be a code violation?


(B) Other Metal Piping. If installed in or attached to a building
or structure, a metal piping system(s), including gas piping,
that is likely to become energized shall be bonded to any of the
following:
(1) Equipment grounding conductor for the circuit that is
likely to energize the piping system
.
There's no need to go any further than #1, if a 20 amp circuit is the likely culprit that may energize the particular piping a #12 is all that is needed. If a 600 amp circuit is likely to energize it go to Table 250.122 and size it accordingly.

Roger
 

charlie b

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I agree with Roger, in that that is how to deal with the bonding jumpers. But I repeat that this thread is not about bonding jumpers. It is about GECs.
 

jaggedben

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I agree with Roger, in that that is how to deal with the bonding jumpers. But I repeat that this thread is not about bonding jumpers. It is about GECs.
The way I read the diagram, the column of items on the right are items to be bonded, not electrodes. The rest of the items are grounding electrode system.
 

mbrooke

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I think not. Your citation is related to bonding jumpers. The original question, and the sketch, are related to grounding electrode conductors. See my code citation in post #2.


Yes, but to me a gas pipe needs a grounding electrode conductor, not a bonding jumper. I guess the question is what guarantee is there that the gas pipe will have an isolating union.
 

roger

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Yes, but to me a gas pipe needs a grounding electrode conductor, not a bonding jumper. I guess the question is what guarantee is there that the gas pipe will have an isolating union.
Well there is 250.52(B) that puts that to bed with or with out isolation which takes us back to 250.104(B)

Roger
 

Dennis Alwon

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The gas pipe cannot be a grounding electrode as mentioned above and often times there is a dielectric fitting between the gas meter and the interior pipes... Of course depending on where the meter is located this would eliminate the gas pipe as an electrode.
 

mbrooke

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I'm surprised the code says that- without isolation the gas pipe will exhibit all the electrical properties of a grounding electrode.
 

mbrooke

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The gas pipe cannot be a grounding electrode as mentioned above and often times there is a dielectric fitting between the gas meter and the interior pipes... Of course depending on where the meter is located this would eliminate the gas pipe as an electrode.
When is the dielectric fitting absent? And where is it present?
 

charlie b

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I won't say that I might have been wrong, but I may have finished a bit short on being right. :angel:
The way I read the diagram, the column of items on the right are items to be bonded, not electrodes. The rest of the items are grounding electrode system.
I see it that way as well (notwithstanding any previous comments). The diagram mentions a detail for bonding metal pipes elsewhere on the same sheet, but it is not in our field of view. So it wasn't clear whether the pipes shown on the right side were all internal to the building, as opposed to extending into the dirt outside the building.

That brings me back to the original question. Yes, a #6 is likely too small. We don't know what the minimum size needs to be, because the OP does not tell us the size of the service conductors. We can infer, however, that a 3/0 is an acceptable bonding conductor size. That is because all the GECs - except those serving the water pipe and the CEE, which have smaller allowances - are 3/0. But I suspect that is overkill. You don't need a 3/0 GEC for services smaller than 1100 MCM, and that would be good for a 600 amp service. The OP mentions something about 200 amp breakers, but it is not clear whether the main board shown on the diagram is rated for 200 amps or for something higher.
 
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