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grounding electrode location

John Frum

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User has a panel array, power house, and house all in a straight line.

panel_array---50'---power_house---80'---house

The plan is to have the n-g bond in the power house and the grounding electrode will also be in the power house.

Is the voltage gradient over 80' between power house and house an issue?

@FilterGuy
@NorthTown2022
 
Seem like you may be asking 2 different questions. Assuming the main panel is in the Power House then placing the ground rod there also is appropriate.
1) Yes, the voltage drop (gradient) of the CONDUCTORS, Hot Legs & Neutral, feeding to the house 80' away has to be taken into account when choosing wire size.
2) The ground wire is then sized based on the conductors. It can be the same size as the conductors or in some cases the code allows downsizing based on a published charts. The ground wire will have a certain amount of characteristic resistance but there should be NO voltage gradient because there is not supposed to be voltage on the ground wire unless there is a fault or short somewhere.
 
Seem like you may be asking 2 different questions. Assuming the main panel is in the Power House then placing the ground rod there also is appropriate.
1) Yes, the voltage drop (gradient) of the CONDUCTORS, Hot Legs & Neutral, feeding to the house 80' away has to be taken into account when choosing wire size.
2) The ground wire is then sized based on the conductors. It can be the same size as the conductors or in some cases the code allows downsizing based on a published charts. The ground wire will have a certain amount of characteristic resistance but there should be NO voltage gradient because there is not supposed to be voltage on the ground wire unless there is a fault or short somewhere.

Sorry I wasn't clear. I'm talking about the voltage gradient between the house electrical system and the earth it sits on.
The house electrical system will be referenced to the earth at the grounding electrode 80' away from the house.
There could be a voltage gradient between earth at the house and the earth at the grounding electrode.
 
Typically you only need one grounding rod near the main panel which is in your Power House then the ground wire runs all the way to the loads. Are you saying there is also a grounding rod at the house? If so then I suppose its possible to get a kind of "earth battery" situation where there is a potential difference over the 80' distance. This would be easy to measure with a meter. For example, if you had galvanized water pipe that is grounded to the electrical system at the house and the ground rod is copper. I'll defer to the electricians on the forum for a better answer.
 
You need grounding electrodes at both structures.
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) GroundingElectrode. Building(s)orstructure(s)supplied by feeder(s) or branch circuit(s) shall have a grounding elec- trode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Screenshot.png
 
I found this.
 
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page 10 of this document is also relevant
 
You need grounding electrodes at both structures.

View attachment 104946

Once upon I time I was told the the best practice was to bond all the ground rods together together so you don't get a high potential difference in voltage on the grounding system due to lightning on one side of the property causing an equipment damaging surge. So the above drawing would have a bond between Building 1 and Building 2 in my mind.

It sounded really reasonable at the time but I can't quickly find a source right at the moment. I'm not saying I'm right, rather asking for any clarity on the matter you can offer. Would it hurt to have them all bonded together? Thanks!
 
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That is my understanding and the understanding of the two electrical engineers (one also was master electrician). Only one bond between Neutral and ground at the main panel with the subpanels keeping a separated neutral and ground (no bond screw). There would be still be 4 wires going back to the main panel from the subpanels, two hots a ground and a neutral.

Each subpanel would have a ground rod connected to the ground bar in the panel and that rod would also be connected to the primary household ground via a #4 conductor installed in the conduit trench and kept outside the buildings. The intent is that if there is reflected or nearby lightning hit that everything is referenced to the best ground via the external bonding cables so that there is a far less chance of current flowing through the wiring between the subpanels. If there is steel well casing, that is also tied into the main household ground. The goal is to keep all grounds at the same potential and if there is difference route a strike via the bonding cables outside of the structure. Note there are no guarantees on what happens with direct lightning strike. Talk to any radio or TV tower engineer. That is what home insurance is for.
 
Once upon I time I was told the the best practice was to bond all the ground rods together together so you don't get a high potential difference in voltage on the grounding system due to lightning on one side of the property causing an equipment damaging surge. So the above drawing would have a bond between Building 1 and Building 2 in my mind.

It sounded really reasonable at the time but I can't quickly find a source right at the moment. I'm not saying I'm right, rather asking for any clarity on the matter you can offer. Would it hurt to have them all bonded together? Thanks!
Personally, I prefer that practice. With US codes, the only change when you do that is to eliminate the neutral-ground bond in the remote building's panel. The one problem that it causes though is circulating ground currents, which may or may not be material.
 
Once upon I time I was told the the best practice was to bond all the ground rods together together so you don't get a high potential difference in voltage on the grounding system due to lightning on one side of the property causing an equipment damaging surge. So the above drawing would have a bond between Building 1 and Building 2 in my mind.

It sounded really reasonable at the time but I can't quickly find a source right at the moment. I'm not saying I'm right, rather asking for any clarity on the matter you can offer. Would it hurt to have them all bonded together? Thanks!
Is that effectively a horizontal ground that makes point a to point b the same potential?
 
That is my understanding and the understanding of the two electrical engineers (one also was master electrician). Only one bond between Neutral and ground at the main panel with the subpanels keeping a separated neutral and ground (no bond screw). There would be still be 4 wires going back to the main panel from the subpanels, two hots a ground and a neutral.

Each subpanel would have a ground rod connected to the ground bar in the panel and that rod would also be connected to the primary household ground via a #4 conductor installed in the conduit trench and kept outside the buildings. The intent is that if there is reflected or nearby lightning hit that everything is referenced to the best ground via the external bonding cables so that there is a far less chance of current flowing through the wiring between the subpanels. If there is steel well casing, that is also tied into the main household ground. The goal is to keep all grounds at the same potential and if there is difference route a strike via the bonding cables outside of the structure. Note there are no guarantees on what happens with direct lightning strike. Talk to any radio or TV tower engineer. That is what home insurance is for.
That would be incorrect. You need both an equipment grounding conductor and a grounding electrode conductor between the buildings if you don't do a neutral-ground connection. The EGC goes with your phases and neutral, and a separate conduit (or direct burial) handles your GEC.

In larger commercial work where you have ground fault protection on your main the option included from the code with multiple neutral-ground bonds would not work, so you need to carry a GEC between buildings.

Both approaches have their advantages and disadvantages. When you don't have a single point ground you end up with circulating currents. That can be a problem with radio equipment and sensitive electronics.
 
Is that effectively a horizontal ground that makes point a to point b the same potential?
Correct and point C as well which what you're after. I tried googling again and can't easily find a graphic.

Edti: I assumed you were talking about Building 1 and 2 in the graphic when you say A and B. I may not be following you though.
 
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That would be incorrect. You need both an equipment grounding conductor and a grounding electrode conductor between the buildings if you don't do a neutral-ground connection. The EGC goes with your phases and neutral, and a separate conduit (or direct burial) handles your GEC.

In larger commercial work where you have ground fault protection on your main the option included from the code with multiple neutral-ground bonds would not work, so you need to carry a GEC between buildings.

Both approaches have their advantages and disadvantages. When you don't have a single point ground you end up with circulating currents. That can be a problem with radio equipment and sensitive electronics.
I guess your reading comprehension was low when I described still needing 4 conductors between panels in addition to the local ground rods.?
 
I guess your reading comprehension was low when I described still needing 4 conductors between panels in addition to the local ground rods.?
You need five. 2x Phase, 1x Neutral, 1x "ground" in one conduit, and 1x grounding electrode conductor in a separate conduit if you do not do a neutral-ground bond at the remote structures.
 
page 10 of this document is also relevant
This is the page mentioned

1659413683916.png

THe key thing is in the first sentence "The NEC allows and sometimes requires multiple points in the system to be tied to earth ground"

Unfortunately, you have hit on the 'sometimes requires' by having multiple buildings. The electrode at each building requirement is a tradeoff that tries to make the best out of several less than great options.
 
Unfortunately, you have hit on the 'sometimes requires' by having multiple buildings. The electrode at each building requirement is a tradeoff that tries to make the best out of several less than great options.
@John Frum is referring to my installation.

With multiple out buildings I am understanding that figure 3 'best' option will be most suitable in my situation. Is there a rule to dictate the gauge of copper conductor used to daisy chain grounding electrodes? Also I suppose the copper conductor should be insulated?
 
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