Grounding a sub-panel.
#1
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Grounding a sub-panel.
I have installed a sub- panel in an a detached cabin on our lot. The supply cable will run from the main house. Since the plumbing will be plastic I am required to drive two stakes joined by copper wire to ground the sub-panel. My understanding is this copper wire is then run to the neutral bus in the sub-panel. Is this correct? If so, why not to the bus where the bare copper wires attach for each circuit when they run to the sub-panel. Hope this makes sense! Thanks.
#2
>I have installed a sub-panel in an a detached cabin on our lot.
> I am required to drive two stakes joined by copper wire to ground the sub-panel.
Correct.
> My understanding is this copper wire is then run to the neutral bus in the sub-panel.
> Is this correct?
No.
> If so, why not to the bus where the bare copper wires attach for each
> circuit when they run to the sub-panel.
That's the correct one.
Did you use a four-wire feeder?
> I am required to drive two stakes joined by copper wire to ground the sub-panel.
Correct.
> My understanding is this copper wire is then run to the neutral bus in the sub-panel.
> Is this correct?
No.
> If so, why not to the bus where the bare copper wires attach for each
> circuit when they run to the sub-panel.
That's the correct one.
Did you use a four-wire feeder?
#4
>Did you run a equipment grounding conductor with your feeder...?
>This information is needed to properly answer your question.
Unnecessary information to give correct answer - the original post contains sufficient information to answer properly.
>This information is needed to properly answer your question.
Unnecessary information to give correct answer - the original post contains sufficient information to answer properly.
#5
250.32(B)(2) of the 2005 NEC allows a feeder without an equipment grounding conductor if all of the requirements are met. If you use this section then you would run the grounding electrode conductor to the neutral bar and bond that to the panel.
Chris
Chris
#7
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Thank you for the help.
My plan is the following:
40 amp breaker in main panel.
Three wire plus bare copper # 8 wire.
At the main panel the black and red attached to breaker. The white to the neutral bus. The copper to the enclosure ( not sure why I can't attach to ground bus, but my book says "enclosure").
At the sub-panel the black and red would be attached to the hot bus bars. The white to the neutral bus. Again, the copper to the enclosure ( as opposed to the ground bus).
The grounding wire attached to the stakes would be #6 copper.
Assuming I have not made a mistake above my problem is, I think, what do I attach the grounding wire from the stakes to?
Once again,I hope this makes sense. Thanks. Patrick
My plan is the following:
40 amp breaker in main panel.
Three wire plus bare copper # 8 wire.
At the main panel the black and red attached to breaker. The white to the neutral bus. The copper to the enclosure ( not sure why I can't attach to ground bus, but my book says "enclosure").
At the sub-panel the black and red would be attached to the hot bus bars. The white to the neutral bus. Again, the copper to the enclosure ( as opposed to the ground bus).
The grounding wire attached to the stakes would be #6 copper.
Assuming I have not made a mistake above my problem is, I think, what do I attach the grounding wire from the stakes to?
Once again,I hope this makes sense. Thanks. Patrick
#8
Originally Posted by raider1
250.32(B)(2) of the 2005 NEC allows a feeder without an equipment grounding conductor
> If you use this section then you would run the grounding electrode
> conductor to the neutral bar and bond that to the panel.
Where does it say to run it to the neutral bar?
The OP already stated that he has a ground bar.
Therefore, regardless of whether it is three- or four-wire feeder, the GEC goes to the ground bar.
It makes sense to him. Let's not add meaningless befuddlement.
#9
Originally Posted by PatrickS
40 amp breaker in main panel. Three wire plus bare copper # 8 wire.
(My comment: Could use 50A, no?)
> At the main panel the black and red attached to breaker.
> The white to the neutral bus. The copper to the enclosure
> (not sure why I can't attach to ground bus...)
Connect to the ground bus.
> At the sub-panel the black and red would be attached to
> the hot bus bars.
Main lugs.
> The white to the neutral bus.
Correct.
> Again, the copper to the enclosure
> (as opposed to the ground bus).
Connect to the ground bus.
> The grounding wire
GEC.
> attached to the stakes would be #6 copper.
Okay.
> what do I attach the grounding wire from the stakes to?
You should use actual ground rod electrode listed for the purpose and an acorn clamp listed for direct burial.
#10
Bolide,
I don't want to add confusion, thats not the reason that I said what I did.
250.32(B)(2) "The grounded 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 and bonding of equipment...."
Just because there is a ground bar doesn't mean that there is an equipment grounding conductor brought with the feeder. That is why I asked if there was an equipment grounding conductor. If it is a three wire feeder without an equipment grounding conductor you are only able to use 250.32 to bond and ground the system.
No a separate building or structure requires a grounding electrode system installed in accordance with 250.50 (250.32(A)) A ground rod is only one of the methods specified in 250.52.
If you have metal underground water pipe, Metal Frame of the building or structure, or according to 2005 NEC a concrete encased electrode, you must use these as part of your grounding electrode system.
Chris
I don't want to add confusion, thats not the reason that I said what I did.
Where does it say to run it to the neutral bar?
The OP already stated that he has a ground bar.
Therefore, regardless of whether it is three- or four-wire feeder, the GEC goes to the ground bar.
Therefore, regardless of whether it is three- or four-wire feeder, the GEC goes to the ground bar.
A detached structure requires a ground rod (or two).
If you have metal underground water pipe, Metal Frame of the building or structure, or according to 2005 NEC a concrete encased electrode, you must use these as part of your grounding electrode system.
Chris
#11
> I don't want to add confusion
I'm afraid you are.
>> Where does it say to run it to the neutral bar?
> 250.32(B)(2)
It does not say that. Running the GEC to the ground bar meets the requirement of this article because: "The grounded conductor ... shall be used for grounding and bonding of equipment, structures, ..."
Connected/bonded means electrically. There is no requirement to land EGCs and GECs on the neutral bus in any panel anywhere.
Whereas it is always correct to land EGCs and GECs on the ground bar in every panel everywhere, number of feeder wires doesn't change this. In the OP's case, landing the GEC on the neutral is incorrect, so insisting that it is a Code requirement to do so is just adding confusion imo.
> Just because there is a ground bar doesn't mean that there is an equipment
> grounding conductor brought with the feeder.
Doesn't matter. GEC may land on the ground bar which is bonded to the ungrounded conductor as required.
> If it is a three wire feeder without an equipment grounding conductor
> you are only able to use 250.32 to bond and ground the system.
GEC may land on the ground bar.
The only necessary issue is that if the OP's installation were a three-wire, then the neutral and ground must be bonded.
The installation is four wires, anyway, so they must not be bonded.
> If you have metal underground water pipe ...
... you better have a four-wire feeder.
I'm afraid you are.
>> Where does it say to run it to the neutral bar?
> 250.32(B)(2)
It does not say that. Running the GEC to the ground bar meets the requirement of this article because: "The grounded conductor ... shall be used for grounding and bonding of equipment, structures, ..."
Connected/bonded means electrically. There is no requirement to land EGCs and GECs on the neutral bus in any panel anywhere.
Whereas it is always correct to land EGCs and GECs on the ground bar in every panel everywhere, number of feeder wires doesn't change this. In the OP's case, landing the GEC on the neutral is incorrect, so insisting that it is a Code requirement to do so is just adding confusion imo.
> Just because there is a ground bar doesn't mean that there is an equipment
> grounding conductor brought with the feeder.
Doesn't matter. GEC may land on the ground bar which is bonded to the ungrounded conductor as required.
> If it is a three wire feeder without an equipment grounding conductor
> you are only able to use 250.32 to bond and ground the system.
GEC may land on the ground bar.
The only necessary issue is that if the OP's installation were a three-wire, then the neutral and ground must be bonded.
The installation is four wires, anyway, so they must not be bonded.
> If you have metal underground water pipe ...
... you better have a four-wire feeder.
#12
Whereas it is always correct to land EGCs and GECs on the ground bar in every panel everywhere
250.24(4) ..."the grounding electrode conductor shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected".
You are not allowed to terminate a GEC at a panel other than the service disconnecting means. 250.32(A)(1) is a exception to this and allows the grounding electrode to be installed at the separate buildings disconnecting means. There is also an exception for a separately derived system.
Chris
#14
Originally Posted by PatrickS
Assuming I have not made a mistake above my problem is, I think, what do I attach the grounding wire from the stakes to?
- Connect the #6 to your ground rods (and/or other available electrodes)
- Use an "acorn" as Bolide mentioned.
- Space the two ground rods at least six feet apart.
- The other side of the grounding wire (the "GEC" that goes out to the ground rods) lands on your grounding bar, just like the branch circuit's grounding conductors do.
- Do not make any connections between the grounding conductors and the neutrals in this panel.
- If you see a green screw up by where you landed the feeder conductors (the #8's), it would be a good idea to remove it and throw it away. If it is tightened, then it will connect the neutrals and the grounds, and you don't want that in this sub-panel.
#16
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Kudos to Rocky Mountain for providing the correct answer to the OP's problem and for doing it in a straight forward, easily understandable manner. It just ain't that complicated.
#18
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To the original poster:
I think that you need to do some more background reading before you continue. When I read your posts, your questions suggest that you don't understand many of the details of this installation. We could answer all of your questions perfectly, and yet not give you good advice because we miss the questions that you don't even know to ask.
1) In _all_ cases, it is entirely appropriate to connect the grounding electrode conductors (the GEC) to the equipment ground bus. The equipment ground bus should be electrically bonded to the enclosure, so connecting the GEC to the ground bus will electrically connect the GEC to the enclosure, as well as to all other electrically 'bonded' metal in the structure.
2) In _some_ cases (three wire feed, or service entrance) the neutral bus is electrically connected (bonded) to ground. In these specific cases, the neutral bus _may_ serve double duty as the ground bus, or you _may_ have a physically separate ground and neutral bus. In these specific cases, the neutral bus will be electrically connected to the enclosure, and will be electrically connected to a ground bus if present. If the neutral bus is serving double duty as the ground bus, then the GEC, as well as all equipment grounding conductors, will be connected to the single neutral/ground bus.
3) Since you ran a 4 wire feeder to your subpanel, you _must_ have a separated ground and neutral bus. In this case, any grounding electrode conductors go to the ground bus.
4) In a detached structure you are required to have grounding electrodes. All _possible_ grounding electrodes must be used (there is a list in article 250, which includes metal water pipes, well casing, rebar in foundations (with exceptions), building steel framing, etc). If no electrodes are already present, then you have to add certain 'made' electrodes (ground rods are the most common type) , and if the only electrode present is metal underground water pipe, then you have to add the 'made' electrodes. But if you have a 'ufer' ground (the uninsulated rebar in the foundation), then this can serve as the necessary grounding electrode, without any additional rods.
-Jon
I think that you need to do some more background reading before you continue. When I read your posts, your questions suggest that you don't understand many of the details of this installation. We could answer all of your questions perfectly, and yet not give you good advice because we miss the questions that you don't even know to ask.
1) In _all_ cases, it is entirely appropriate to connect the grounding electrode conductors (the GEC) to the equipment ground bus. The equipment ground bus should be electrically bonded to the enclosure, so connecting the GEC to the ground bus will electrically connect the GEC to the enclosure, as well as to all other electrically 'bonded' metal in the structure.
2) In _some_ cases (three wire feed, or service entrance) the neutral bus is electrically connected (bonded) to ground. In these specific cases, the neutral bus _may_ serve double duty as the ground bus, or you _may_ have a physically separate ground and neutral bus. In these specific cases, the neutral bus will be electrically connected to the enclosure, and will be electrically connected to a ground bus if present. If the neutral bus is serving double duty as the ground bus, then the GEC, as well as all equipment grounding conductors, will be connected to the single neutral/ground bus.
3) Since you ran a 4 wire feeder to your subpanel, you _must_ have a separated ground and neutral bus. In this case, any grounding electrode conductors go to the ground bus.
4) In a detached structure you are required to have grounding electrodes. All _possible_ grounding electrodes must be used (there is a list in article 250, which includes metal water pipes, well casing, rebar in foundations (with exceptions), building steel framing, etc). If no electrodes are already present, then you have to add certain 'made' electrodes (ground rods are the most common type) , and if the only electrode present is metal underground water pipe, then you have to add the 'made' electrodes. But if you have a 'ufer' ground (the uninsulated rebar in the foundation), then this can serve as the necessary grounding electrode, without any additional rods.
-Jon
#19
> (ground rods are the most common type)
If you have a trench open, some #2 or #4 run out into the ditch is a nice idea.
I've heard that up to 75' helps to dissipate energy from lightning strikes.
Ground rods should be past the roof drip line.
Too close to the house is believed to be too dry in some cases to be as effective as rods under direct rainfall.
I doubt that anyone can deny that soil moisture directly correlates with conductivity.
If you have a trench open, some #2 or #4 run out into the ditch is a nice idea.
I've heard that up to 75' helps to dissipate energy from lightning strikes.
Ground rods should be past the roof drip line.
Too close to the house is believed to be too dry in some cases to be as effective as rods under direct rainfall.
I doubt that anyone can deny that soil moisture directly correlates with conductivity.
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Originally Posted by bolide
Ground rods should be past the roof drip line.
Too close to the house is believed to be too dry in some cases to be as effective as rods under direct rainfall.
I doubt that anyone can deny that soil moisture directly correlates with conductivity.
Too close to the house is believed to be too dry in some cases to be as effective as rods under direct rainfall.
I doubt that anyone can deny that soil moisture directly correlates with conductivity.
-Jon
#21
Money spent on extra grounding electrodes in a residential application is a waste of resources, IMO. I recommend using all the electrodes present (which is required); if none are present, install two ground rods, and call it a day.
One electrician's opinion (but shared by many).
One electrician's opinion (but shared by many).