jwjrw
Senior Member
I didnt know we had a state electrical code. Every county I have worked in require 2. I know meck county has it on the web site or did at one time.
ground rod ques?
- Thread starter wireman1
- Start date
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I didnt know we had a state electrical code. Every county I have worked in require 2. I know meck county has it on the web site or did at one time.
jwjrw
Senior Member
OK I did know about NC amendments but thought he meant a seperate code.
Thank you for the links.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100129-1122 EST
jaylectricity:
No you can not just use your ohmmeter.
In reality if you are just playing around and want to experiment and get an estimate you could use your DC ohmmeter. However, there are some problems.
If you attempt to measure the resistance of a conductive liquid like water with dissolved salts, most non-distilled water, then with DC excitation you will notice a gradual increase in the resistance vs time. If you have a Simpson 260, then you can switch the +/- selector back and forth and simulate a low frequency AC signal. I did a quick check in our tap water in a glass with a 270, and its test leads. My initial reading was 35,000, and after a few seconds 45,000 ohms on the 10,000 range.
A better experiment is with a 28 V output isolation transformer at 60 Hz, an ammeter, and voltmeter. Use two electrodes spaced maybe 30 ft apart. Use a 0.1 ohm resistor and voltmeter to measure current so you do not burn out expensive Fluke fuses. This will give you the resistance of both electrodes and the earth in series. In my area I measure 10 to 20 ohms with 8 ft rods in a clay loam soil. This is not the NEC fall of potential method but gives you a crude estimate. You can expand this experiment to do a fall of potential measurement. I use a 2 A output transformer and don't keep the load on very long. I can get a moderate correlation between the Simpson 260 reading and my 28 V AC test.
Before supplying power to the 28 V transformer and with the secondary open make voltage measurements between the electrodes, and between isolated probes (screwdrivers) in the earth between the test rods. Always be careful because there may be some ground areas with large potential differences. If you see more than 1 volt of residual ground voltage, then do the experiment somewhere else. A 1 volt error in 28 V is not a signification error for a very crude experiment. Commercial instruments use AC excitation but not at 60 Hz to avoid the residual 60 Hz error signals.
Do a Google search for --- fall of potential ground test --- first result today was:
http://www.kilowattclassroom.com/Archive/GndTestArticle.pdf
Other than for your education don't bother. Just drive two ground rods.
.
jaylectricity:
No you can not just use your ohmmeter.
In reality if you are just playing around and want to experiment and get an estimate you could use your DC ohmmeter. However, there are some problems.
If you attempt to measure the resistance of a conductive liquid like water with dissolved salts, most non-distilled water, then with DC excitation you will notice a gradual increase in the resistance vs time. If you have a Simpson 260, then you can switch the +/- selector back and forth and simulate a low frequency AC signal. I did a quick check in our tap water in a glass with a 270, and its test leads. My initial reading was 35,000, and after a few seconds 45,000 ohms on the 10,000 range.
A better experiment is with a 28 V output isolation transformer at 60 Hz, an ammeter, and voltmeter. Use two electrodes spaced maybe 30 ft apart. Use a 0.1 ohm resistor and voltmeter to measure current so you do not burn out expensive Fluke fuses. This will give you the resistance of both electrodes and the earth in series. In my area I measure 10 to 20 ohms with 8 ft rods in a clay loam soil. This is not the NEC fall of potential method but gives you a crude estimate. You can expand this experiment to do a fall of potential measurement. I use a 2 A output transformer and don't keep the load on very long. I can get a moderate correlation between the Simpson 260 reading and my 28 V AC test.
Before supplying power to the 28 V transformer and with the secondary open make voltage measurements between the electrodes, and between isolated probes (screwdrivers) in the earth between the test rods. Always be careful because there may be some ground areas with large potential differences. If you see more than 1 volt of residual ground voltage, then do the experiment somewhere else. A 1 volt error in 28 V is not a signification error for a very crude experiment. Commercial instruments use AC excitation but not at 60 Hz to avoid the residual 60 Hz error signals.
Do a Google search for --- fall of potential ground test --- first result today was:
http://www.kilowattclassroom.com/Archive/GndTestArticle.pdf
Other than for your education don't bother. Just drive two ground rods.
.
jwjrw
Senior Member
Yep did a coffee shop put 20 feet #4 in concrete, 2 ground rods, think it was 1/0 to building steel and water pipe.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You didn't need the rods with a CEE.
rcarroll
Senior Member
- Location
- Fort Collins, Colorado
Apparently someone thinks so.:roll:
electricmanscott
Senior Member
- Location
- Boston, MA
That's true. I usually run #4 just because I have it on hand for GEC or BC to water pipe. The rods themselves are equivilent to #6 as far as current carrying goes. Requiring anything more is not improving anything.
- Location
- Bremerton, Washington
Most electricians and inspectors don't understand this.
The code allows two wires and three clamps.
The GEC goes to grounding electrode.
From there to other electrodes its a bonding jumper.
See 150.64(F)(1) in the 2008 NEC and note the gray boxes
This is a change for the 2008 NEC and its much better wording. I can see why before it was not clear.
The code allows two wires and three clamps.
The GEC goes to grounding electrode.
From there to other electrodes its a bonding jumper.
See 150.64(F)(1) in the 2008 NEC and note the gray boxes
This is a change for the 2008 NEC and its much better wording. I can see why before it was not clear.
jwjrw
Senior Member
I can only tell you right or wrong here you get 2 ground rods even with a cee.
Can you show me where it says you dont need supplemental rods if you have an cee? Maybe next time Ill try to fight it.
I can only tell you right or wrong here you get 2 ground rods even with a cee.
Can you show me where it says you dont need supplemental rods if you have an cee? Maybe next time Ill try to fight it.
Take note of the wording in the article sections below.
That would mean only one (any one) of the electrodes in 250.52(A) (2) through (8) needs to be used.
Roger
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I can only tell you right or wrong here you get 2 ground rods even with a cee.
Can you show me where it says you dont need supplemental rods if you have an cee? Maybe next time Ill try to fight it.
As Roger stated you only need to supplement the water pipe. If a CEE is present then you must use it. This would become your supplemental electrode. If there is no water pipe (or it's plastic) then you only need one electrode. If someone is saying that you need the water pipe, a CEE and ground rods they're not enforcing the NEC correctly.
electricmanscott
Senior Member
- Location
- Boston, MA
I can only tell you right or wrong here you get 2 ground rods even with a cee.
Can you show me where it says you dont need supplemental rods if you have an cee? Maybe next time Ill try to fight it.
It's not wrong to do it but it isn't right to require it. If we (us and inspectors) just read the book once in a while we wouldn't be having these issues.
jwjrw
Senior Member
Like alot of electricians I struggle in some areas that I havent got alot of experience in. Looking at plans tells you what to do not why. I am trying hard to learn what I dont know yet. The things I have learned over the years I know and do well. The things I need to learn I hope chatting on here will help with. Thanks guys your a big help.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Like alot of electricians I struggle in some areas that I havent got alot of experience in. Looking at plans tells you what to do not why. I am trying hard to learn what I dont know yet. The things I have learned over the years I know and do well. The things I need to learn I hope chatting on here will help with. Thanks guys your a big help.
Many of us do things certain ways because that's the way we were taught. Doesn't mean that those methods are always required or correct. Also the NEC changes every three years so what was applicable yesterday may not be required today. I see this out in the filed quite often. Doing things that are not required because someone was told (incorrectly) that it is required.
jwjrw
Senior Member
Yep changes every 3 years and wording that sometimes can be difficult to interpert what they really intended makes it a lot to learn and something you have to keep up with.
The ground rods were on the plans I didnt question that.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I did a job where I drove a ground rod for a temp. pole and I put a cee in the footers of the structure. At the end of the job I did a three point test and found the cee to have 13 ohms while the rod had 93 ohms. When I added a second rod I got it down to 89 ohms.
So does it really add to the 13 ohm CEE to include those rods also. I don't think so.
So does it really add to the 13 ohm CEE to include those rods also. I don't think so.
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