- Location
- Bremerton, Washington
- Occupation
- Master Electrician
The law of demishing (sp) returns, 2 rods is reduced by 60%, 3 is 40%.
Its not worth any time on why, just drive 2 and go home.
Ground rods
- Thread starter hhsting
- Start date
- Status
Its not worth any time on why, just drive 2 and go home.
hhsting
Senior Member
- Location
- Glen bunie, md, us
- Occupation
- Junior plan reviewer
WasGSOHM
Senior Member
- Location
- Montgomery County MD
- Occupation
- EE
. . .diminishing returns.
1 rod, 25 ohms
2, 23
3, 22
more, 22
The resistance graph is asymptotic at more than 3 rods.
1 rod, 25 ohms
2, 23
3, 22
more, 22
The resistance graph is asymptotic at more than 3 rods.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Which has nothing to do with our present AC power grid.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
I have a paper from Mike Holt and 1984 IEEE on why 25 ohms but its too large to attach. But basically he said 25 ohms is calculated based on 7 miles of 8 AWG, on the premise of earth wires, or using the earth as a ground return, as related to telegraph systems
WasGSOHM
Senior Member
- Location
- Montgomery County MD
- Occupation
- EE
And scaling this value up or down to bring us into 2020 may not be easy.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
In 10 years electricians won't even know what a ground rod is.
Carultch
Senior Member
- Location
- Massachusetts
Thanks for initiating the explanation to address my concern about the inconsistency of this rule. Now it is making a lot more sense.
hhsting
Senior Member
- Location
- Glen bunie, md, us
- Occupation
- Junior plan reviewer
See post #18 care to explain how chart helped you made sense?
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WasGSOHM
Senior Member
- Location
- Montgomery County MD
- Occupation
- EE
Please connect the dots.
No metal pipes in the kitchens and baths?
No grounded metal anywhere?
Extraordinary claims call for extraordinary proof but this may not be an extraordinary claim. I can't say at this point.
His point being, that if all the metal you mention is bonded properly, connection to dirt has no meaning or effect.
That and the now normal use of an ufer.
Another point illustrated in the diagram is the spacing of the rods.
A ground rod discharging to the ground affects the earth in its immediate vicinity. Placing the second rod too close does not allow the rods to be used to their best advantage. Six feet is code, but ten feet gives better reduction of ohms on an 8 foot rod.
A ground rod discharging to the ground affects the earth in its immediate vicinity. Placing the second rod too close does not allow the rods to be used to their best advantage. Six feet is code, but ten feet gives better reduction of ohms on an 8 foot rod.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
They will be using fiberglass rods because they cost less
mikeames
Senior Member
- Location
- Gaithersburg MD
- Occupation
- Teacher - Master Electrician - 2017 NEC
New construction is using concrete encased/UFER/ rebar etc....
BTW what does UFER mean or stand for. I read from EC&M its the name of the engineering ( Herbert G. Ufer ) who created it as a solution. Ill buy that unless someone tells me otherwise.
On Solid Ground: Defining and Understanding UFER Ground
What is a “UFER “ground? This common question is worthy of a detailed explanation. “UFER” ground is slang for what the National Electrical Code (NEC) addresses as a concrete-encased grounding electrode. While the term “UFER” does not appear in the Code, it is used by many in the industry and is...
Joe.B
Senior Member
- Location
- Myrtletown Ca
- Occupation
- Building Inspector
Ufer is the last name of an engineer who "discovered" or designed the first concrete encased electrode. I think he was an army corp engineer who was trying to solve static issues in desert conditions, specifically for munition storage? I forget the whole story, it's probably on wikiNew construction is using concrete encased/UFER/ rebar etc....
BTW what does UFER mean or stand for. I read from EC&M its the name of the engineering ( Herbert G. Ufer ) who created it as a solution. Ill buy that unless someone tells me otherwise.
On Solid Ground: Defining and Understanding UFER Ground
What is a “UFER “ground? This common question is worthy of a detailed explanation. “UFER” ground is slang for what the National Electrical Code (NEC) addresses as a concrete-encased grounding electrode. While the term “UFER” does not appear in the Code, it is used by many in the industry and is...www.ecmag.com
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Some engineers say twice the length of a rod. 10' rod calls for 20' spacing.. I imagine at some point we hit diminishing returns
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
All has to do with "sphere of influence" which will vary depending on soil conditions.
I think studies have shown you need at least 6 feet separation in most any soil conditions or what you gain is pretty minimal.
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