phill73
Member
- Location
- petersburg, MI. USA
An 8 foot ground rod is rated at #6 copper. Is a 10 foot ground rod rated higher?
10 foot ground rod
- Thread starter phill73
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luckylerado
Senior Member
- Location
- Lake of the Ozarks
250.66(A) is I think what you are referring to and it applies to both 8' and 10' grounding rods.
phill73
Member
- Location
- petersburg, MI. USA
I am referring to 250-66(a). The reason I am asking is I am installing a new 800a service and the only grounding method I have is rods. I did not know if the 10 foot rod would give me more for a fault.
- Location
- Bremerton, Washington
The purpose of a ground rod is not to clear a line to case fault. Ground rods stabilize the voltage and provide protection from lightning or line surges.
My best advice is to "drive two and go home"
However if a ufer ground is present you are required to use it.
My best advice is to "drive two and go home"
However if a ufer ground is present you are required to use it.
luckylerado
Senior Member
- Location
- Lake of the Ozarks
The same is true of building steel and metal underground water pipe. If they are present they are required to be bonded together to form the GES
five.five-six
Senior Member
- Location
- california
I thought metal gas pipe as well.
luckylerado
Senior Member
- Location
- Lake of the Ozarks
Bonded yes but never as a grounding electrode.
- Location
- Simi Valley, CA
Technically the code says that you are supposed to have 8' of rod in the ground, so if you leave 6" sticking out, you are not meeting the code. With the 10' rod it's not an issue.
Carultch
Senior Member
- Location
- Massachusetts
Why even make an 8 ft ground rod, if it doesn't meet the code? What application would there be, where you would exhaust the entire length of the ground rod just to meet code required embedment?
And, in a physical sense, nothing special happens at 96th inch of embedment, that would make 95 inches of embedment significantly insufficient. There's gotta be a continuous function here, relating embedment depth to the required performance as a grounding electrode.
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Carultch
Senior Member
- Location
- Massachusetts
If you "drive two and go home", what electrical specs will that cover you for?
Certainly there has got to be a time when you exceed the capacity of your default two ground rods embedded 8 ft at 6 ft separation.
jeremysterling
Senior Member
- Location
- Austin, TX
I worked a residential service upgrade last year, and thinking alike with Tom, I drove two 8' rods (fully in soft Pecan bottom). I ran #6 per NEC. The inspector arrived and asked me to remove the #6 and install #4 in its place. He said his boss had come to the conclusion that if the NEC says that #6 is good for one rod, then #4 should be good for two!
His request wasn't that hard, so I laughed to myself and ran the #4.
kwired
Electron manager
- Location
- NE Nebraska
A 10 foot rod would still need a supplemental rod unless you verified the first was 25 ohms or less.
- Location
- Massachusetts
Every application of an 8' rod.
We are required to drive it below grade to get the 8'.
There is also a code section requiring we don't leave it sticking up to be a hazard.
Here is part of 250.53(G)
- Location
- Massachusetts
Tony, it helps if you understand the NEC requirements.
If we drive just one ground rod the inspector can require ground resistance testing as your link describes.
On the other hand if we drive at least two ground rods no testing is required.
It's quicker, easier and meets the requirements to do exactly what Tom. Baker suggested.
- Location
- Massachusetts
Certainly job specs can require more than 'two and go home' but the NEC never requires more than that.
What capacity do you feel is being exceeded and how is it calculated?
- Location
- Simi Valley, CA
Well you can drive it all the way in and then use a clamp approved for burial, but I don't see that very often. I do agree with your question about why they make an 8 footer.
kwired
Electron manager
- Location
- NE Nebraska
Probably no significant difference at 94 or even 85 inches, but you have to set a minimum someplace and 8 feet is what they decided. I guess another option is to at least specify a minimum resistance and if that can be achieved with a 2 inch long rod in a specific situation then so be it, but I think they figured it is simpler and gets us "good enough" in most cases to just go with no more then two 8 foot rods. If it isn't good enough chances are a third doesn't make it significantly better either.
Carultch
Senior Member
- Location
- Massachusetts
I'm thinking high amperage services, like 4000A. Or maybe high fault currents, or high voltages. It might also relate to the soil properties, instead of the service electrical specs.
I'm not familiar with what property of a service defines the required amount of Earth bonding, but I would like to know how to anticipate "uncharted territory" for which "two and go home" will not be enough. It very well could be, that this is an unrealistic situation to expect.
kwired
Electron manager
- Location
- NE Nebraska
Grounding electrodes are not about clearing faults. If a rod is the only available electrode doesn't matter if you have 100 amps of service or 4000 amps of service, that rod (plus a supplemental rod if you don't want to measure resistance) is good enough for either application as a grounding elecrode.
An acceptable 25 ohm rod installation will not let enough current flow to even trip a 15 amp breaker. Even @ 277 volts the 25 ohm rod only lets about 11 amps of current flow.
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