Grounding and Bonding in Afghanistan

Status
Not open for further replies.
K

Kyle54

Member
I recently took a job in Afghanistan, I am on a Military base handling G and B issues. We are in a very rocky region, Our company has requested we drive ground rods at every panel, on this base alone, we have over 300 panels. At 90% to earth I can drive a rod 3 to 5 ft, @ 45% to earth I can drive a rod 4 to 6 ft, We have dug our trenches 30ins. deep and have laid our rods. This pace is to slow and at the rate we are going it will take too long. I have had success in four locations digging a small hole 10 to 12 ins. deep and driving a rod @ less than 45% 9 ft in to the ground with a Jack hammer. The tip of the rod is deeper than 30ins. and our 9ft rod surrounded by 8 ft of soil. With one rod I have readings greater than 25 ohms, but less than 100 ohms, With two rods I have made compliance with NEC at less than 25 ohms in two locations. It is known through the region everyone is having a very difficult time in reaching the 25 ohms or less. Although this is not NEC compliant in placement of the GEC, does anyone agree or have any input in solving this? Please understand, we are aware of products to help in bringing down resistance, but getting materials out here is very difficult. My other question to all of you, is in bonding our grounded conductor and ground at the first means of disconnect. Here is a scenerio, I have prime power feeding an 800amp service, that service feeds three 400amp I-line panels which feeds several 100 to 225amp subpanels. I am aware of bonding at the first means of disconnect, therefor I am bonding at the 800amp service, but our I-lines are several feet away, anywhere from 30 to 100 ft away, my coworkers and I have been discussing placing a bond @ the 400 amp I-lines and isolating at our subpanels. We are serving many of our men in uniform and any input would be greatly appreciated to help us keep them safe. Thank you for your assistance, I look forward to reading it.
Kyle54
 
Kyle54 said:
It is known through the region everyone is having a very difficult time in reaching the 25 ohms or less.
Click to expand...
Two ground rods can have a resistance of 1 billion ohms or more by the NEC, see 250.56.

I didn't read too closely to the rest of your post, please break it up into paragraphs in the future, it makes it easier to read.
 
Only bond at the first disconnect means and then keep the neutrals and grounds separated unless you are buiding an sds at a xformer where you start the process again. Putting extra ground rods creates ground loops where neutral and ground current can mix and cause problems. The ground is not intended to carry load current only fault current.
 
peter d said:
Bonding and earthing are two separate things. We are relying on the low impedance conductors or raceways (bonding back to the source), not the earth, for fault clearing.
Click to expand...
Isnt that what I said but in english??? I will type slower this time. Bond at the first disconnect means. (to the neutral which is connected to the source I would think).
 
Don't get too concerned with 25 ohms. If you are trenching in power, lay the ground rods in the ditch, 6 ft apart, 30" deep.

Now, how is this being powered? From a generator? If so, you must install a system bonding jumper at the generator, ie from the neutral to the case of the generator and ground rods at the generator.

Does the generator have a main disconnect?

We need to determine where the system bonding jumper and GEC connection can be made.
 
George Stolz said:
What voltage of fault current are you intending to clear with that path?
Click to expand...
Are you trying to trick me you little devil you. That is not in the christmas spirit. Being that the op didnt state the voltage it would be verry difficult to guess. BTW Which path are you talking about the ground path or the source path? Being he didnt mention any xformers I will guess a 3 phase 208/120. Did I win a cookie?? Ive got my own milk.
 
quogueelectric said:
Are you trying to trick me you little devil you. That is not in the christmas spirit.
Click to expand...
Not trying to trick you, trying to pin you down to understand what you are saying to verify it's accuracy.

Being that the op didnt state the voltage it would be verry difficult to guess.
Click to expand...
Agreed, but play along.

BTW Which path are you talking about the ground path or the source path?
Click to expand...
The path you described - service neutral to earth to utility transformer.

Being he didnt mention any xformers I will guess a 3 phase 208/120. Did I win a cookie?? Ive got my own milk.
Click to expand...
No, but I might have a serving of crow waiting for ya. :)

The earth path is not intended for fault current from 480V or 240V or 208V or 120V, as Peter said.
 
George Stolz said:
Not trying to trick you, trying to pin you down to understand what you are saying to verify it's accuracy.

Agreed, but play along.

The path you described - service neutral to earth to utility transformer.

No, but I might have a serving of crow waiting for ya. :)

The earth path is not intended for fault current from 480V or 240V or 208V or 120V, as Peter said.
Click to expand...
That is why I would never say anything that silly. The source path certainly is though. I dont get the chance to tweak Peter up that often so when he throws up a softball for me I feel I gotta hit it. We can all go back to keeping the troops safe now. Kyle the thought of bonding the neutral in more than one place will actually make the install MORE dangerous. Dont do it.
 
Last edited:
quoquelectric said:
That is why I would never say anything that silly.
Click to expand...
It sure looked like that's what you said.

Edit:
quogueelectric said:
The ground is not intended to carry load current only fault current.
Click to expand...

Anyway, I'll back up and read closer...

Kyle54 said:
We are in a very rocky region, Our company has requested we drive ground rods at every panel, on this base alone, we have over 300 panels.
Click to expand...
Although tiring, the request is legal. See 250.54. The ground rods installed downstream of the service disconnects of the systems would be considered auxiliary grounding electrodes. If connected to the EGC of the "subpanels" (as directed by that section) then there should not be any neutral current flowing on them. If there becomes an issue, 250.6 would have you remove the auxiliary connections.

Kyle54 said:
I am aware of bonding at the first means of disconnect, therefor I am bonding at the 800amp service, but our I-lines are several feet away, anywhere from 30 to 100 ft away, my coworkers and I have been discussing placing a bond @ the 400 amp I-lines...
Click to expand...
That would be a violation of 250.142. If you are concerned that the bonding path will not be sufficient, you should upsize the Equipment Grounding Conductors (EGCs) serving the subpanels.

Kyle54 said:
...and isolating at our subpanels.
Click to expand...
Not quite sure what you mean by this statement, but I take it to mean that you would omit the EGC in the feeders to the subpanels. That would not be compliant with 250.142.
 
Last edited:
George Stolz said:
It sure looked like that's what you said.

Edit:


Anyway, I'll back up and read closer...
Click to expand...
I will attempt to clarify as we all know this is a topic of much confusion. Here is original statement with commentary in prentheses .
"Only bond at the first disconnect means and then keep the neutrals and grounds separated unless you are buiding an sds at a xformer where you start the process again.(I am good up till here)
Putting extra ground rods creates ground loops where neutral and ground current can mix and cause problems.(partially true about ground loops but was thinking about the extra BOND jumpers he was talking about and did not express myself correctly. If only ground rods and no bond jumpers are installed neutral current will not mix. However if he installed the bond jumpers he was talking about this will cause a dangerous mix of ground and neutral current. I want to be crystal clear on this point).
The ground is not intended to carry load current only fault current." ( A more correct wording would have been ground wire/system. Not the dirt.)
Did this get clearer for anyone?? I am not stopping till I get my cookie.
__________________
 
Kyle54 said:
Our company has requested we drive ground rods at every panel, on this base alone, we have over 300 panels.....
My other question to all of you, is in bonding our grounded conductor and ground at the first means of disconnect. Here is a scenerio, I have prime power feeding an 800amp service, that service feeds three 400amp I-line panels which feeds several 100 to 225amp subpanels.

I am aware of bonding at the first means of disconnect, therefor I am bonding at the 800amp service, but our I-lines are several feet away, anywhere from 30 to 100 ft away,

my coworkers and I have been discussing
placing a bond @ the 400 amp I-lines and isolating at our sub-panels.

We are serving many of our men in uniform and any input would be greatly appreciated to help us keep them safe. Thank you for your assistance, I look forward to reading it.
Kyle54
Click to expand...

First I am not to be considered an expert,.. but I think driving supplemental ground rods will do very little to help...

I also think that re-bonding the neutral at the 400 amp panels is a violation of the NEC


I think you should take a look and see how many improper grounded to grounding connections there are ,.. I think you are going to find many of them..
start with the 300 sub panels there should be isolated neutrals , there should also be a grounding conductor for connecting all the metal stuff together .

I will try to find stuff to link to that might help you .. Good luck ,.. Merry Christmas , be safe .
 
Status
Not open for further replies.
Top