Grounding Electrode System

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pfactor2

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Would it be acceptable, on a 300 amp 1phase service 350kcmil service entrance conductors, to bond a 3/4 cold water pipe that runs under ground (10ft or more) with required #2 from the main disconnect neutral bar. Then a #6 bare to two ground rods six feet apart. The water pipe does terminate at the water service so the building interior water pipe system is bonded as well?
 
Sounds fine to me. All of the electrodes of the GES are permitted to be bonded together.

1113918256_2.jpg
 
pfactor2 said:
Would it be acceptable, on a 300 amp 1phase service 350kcmil service entrance conductors, to bond a 3/4 cold water pipe that runs under ground (10ft or more) with required #2 from the main disconnect neutral bar. Then a #6 bare to two ground rods six feet apart. The water pipe does terminate at the water service so the building interior water pipe system is bonded as well?
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You can save on the installation of one ground rod by going for just one ground rod, because I feel that, 2 ground rod at 6 feet is only, as good as, just one ground rod. For the effectiveness of the 2nd rod the separation should be at least 2.1 times the ground rod length.
 
LISHAJI said:
You can save on the installation of one ground rod by going for just one ground rod, because I feel that, 2 ground rod at 6 feet is only, as good as, just one ground rod. For the effectiveness of the 2nd rod the separation should be at least 2.1 times the ground rod length.
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The NEC requires two rods unless you can prove that one rod has a resistance of 25 ohms or less.
 
perfect for my question and i believe what you are saying is that i can do this:

i have two ground rods i want to install on the way to the same end of the house the gas is at. so i may use bare #4 (200A service) to go to my two ground rods, then go to the gas pipe. correct? at least that what i think you said. (also for above post, couldn't he use the water pipe w/in five feet AS the second grounding electrode if he only wants to pound in one?)
 
bullheimer said:
perfect for my question and i believe what you are saying is that i can do this:

i have two ground rods i want to install on the way to the same end of the house the gas is at. so i may use bare #4 (200A service) to go to my two ground rods, then go to the gas pipe. correct? at least that what i think you said. (also for above post, couldn't he use the water pipe w/in five feet AS the second grounding electrode if he only wants to pound in one?)
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No if the water pipe qualifies an an electrode then it must be used. It also must be supplemented by at least one additional electrode. Two ground rods would be required to be considered the supplemental electrode unless the resistance of one rod is 25 ohms or less.
 
Your termination to the water pipe must be within 5ft of where it enters the building - with an exception for industrial locations.
 
Busted!

Busted!

No. it is not within 5ft. This 3/4 is a hose bib stub up on wall 5ft from service. There is another hose bib 35/40ft away that originated inside the bulding. The building is a funeral home, don't think that can pass as industrial location. Rather not have to run a #2 ,mostly due to obstacles, 35/40ft. There is possibly a water pipe closer in a unfinished room adjacent to the service location. So any ideas?
 
pfactor2 said:
No. it is not within 5ft. This 3/4 is a hose bib stub up on wall 5ft from service. There is another hose bib 35/40ft away that originated inside the bulding. The building is a funeral home, don't think that can pass as industrial location. Rather not have to run a #2 ,mostly due to obstacles, 35/40ft. There is possibly a water pipe closer in a unfinished room adjacent to the service location. So any ideas?
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just run the wire to where the water enters the building.
 
infinity said:
The NEC requires two rods unless you can prove that one rod has a resistance of 25 ohms or less.
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Yep thats correct, however, this would work, only if the resistance reading is a little greater than 25 ohms for one rod, but not very far from it, then you can add a second at 6ft apart and hope to get 25 ohm. On the other hand, if it is 50 ohms you cannot certainly hope to get 25 ohms by installing a second rod at 6ft. Because each driven rod has an interfacing hemisphere of earth, see below, required to make complete electrical connection to earth. If multiple rods are driven closer than the diameter of this hemisphere, the connection is incomplete, and the effectiveness of those additional rods are reduced proportionately and, in reality, wasted.
grounding.jpg
 
Nobody ever said that we would add the second ground rod to get the resistance below 25 ohms. If the first ground rod has a resistance above 25 ohms, add a second. We do not care at that point what the total resistance is, it coukld still be over 1000 ohms and we have met the code. All it says is that the second electrode "shall not be less than 6'" from the original ground rod. Don't try to make the code say more than it says.....
 
haskindm said:
Nobody ever said that we would add the second ground rod to get the resistance below 25 ohms. If the first ground rod has a resistance above 25 ohms, add a second. We do not care at that point what the total resistance is, it coukld still be over 1000 ohms and we have met the code. All it says is that the second electrode "shall not be less than 6'" from the original ground rod. Don't try to make the code say more than it says.....
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Sure, 1000 ohms could be acceptable, and maybe would fly with some inspectors. However, as a reminder to NEC 90.1(c), the code is not meant to be a design specification and does not guarantee safety. Its should not be used as a substitute to sound Engineering Judgement.
 
pfactor2, whos busted? the code clearly states that "interior metal water piping more than 5 feet from the point of entrace shall not be used as a part of the grounding electrode systemor as a conductor to interconnect electrodes that are part of the grounding electrode system" see section 250.52 (A)(1)
 
haskindm said:
Nobody ever said that we would add the second ground rod to get the resistance below 25 ohms. If the first ground rod has a resistance above 25 ohms, add a second. We do not care at that point what the total resistance is, it coukld still be over 1000 ohms and we have met the code. All it says is that the second electrode "shall not be less than 6'" from the original ground rod. Don't try to make the code say more than it says.....
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I Agree

LISHAJI said:
Sure, 1000 ohms could be acceptable, and maybe would fly with some inspectors. However, as a reminder to NEC 90.1(c), the code is not meant to be a design specification and does not guarantee safety. Its should not be used as a substitute to sound Engineering Judgement.
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There is no reason for it not to fly. That is what the code calls for. Your so called sound engineering judgment is just a reason to increase the cost of the job. I will say that there are situations where, yes, there is good reason to follow strict guide lines but there are times and situations where you must know when it is not really necessary.
 
ceb58 said:
I Agree



There is no reason for it not to fly. That is what the code calls for. Your so called sound engineering judgment is just a reason to increase the cost of the job. I will say that there are situations where, yes, there is good reason to follow strict guide lines but there are times and situations where you must know when it is not really necessary.
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Expensive, yes I suppose. Also in support of your statement, here is an article from ECMWEB
Who cares about 25 ohms or less?

However, my concern is not so much power quality, but its more safety, so if NEC doesn't require it, I always make it a point to put in my Specifications. At many instances, concrete foundations provide lesser grounding resistance than the electrical ground (thanks to this don't care policy) which in my view is a safety hazard to people and is some cases failure of devices during lightning surges.
 
LISHAJI said:
Expensive, yes I suppose. Also in support of your statement, here is an article from ECMWEB
Who cares about 25 ohms or less?

However, my concern is not so much power quality, but its more safety, so if NEC doesn't require it, I always make it a point to put in my Specifications. At many instances, concrete foundations provide lesser grounding resistance than the electrical ground (thanks to this don't care policy) which in my view is a safety hazard to people and is some cases failure of devices during lightning surges.
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You will have to explain to me how a resistance of 25-ohms or less provides additional safety. Unless you are able to get the resistance of a ground rod to around 2 ohms or less it will not trip a 20 amp breaker with a 120 volt fault to the ground rod in a reasonable amount of time. In the event of lightning, the voltage is so high that a resistance difference of a few (or a few hundred) ohms would be negligible. The code making panels understand that requiring a low resistance on ground rods would serve no purpose so they do not require it.

Just use Ohm's law. If we apply 120 volts to a 25 ohm resistance there will be 4.8 amps flowing, so you will not trip a 20-amp breaker.
Lower the resistance by half to 10 ohms and there will be 12-amps flowing, so still no breaker trip.

Lower the resistance to 5 ohms and you will see 24 amps flowing which MAY eventually trip a 20-amp breaker, but I wouldn't want to hold my breath waiting for it!

Ground rods serve a purpose, but it is NOT tripping overcurrent devices!

If you have 1,000,000 volts in a lightning strike and a 25-ohm resistance you would measure 40,000 amps. If you had a resistance of 100 ohms you would only measure 10,000 amps. I don't see where that would make a big difference in the trip time of a breaker.

Grounding does what it does, it is not magic. Requiring low resistance on a ground rod is a waste of time and money and does not add to the safety of an installation.
 
haskindm said:
You will have to explain to me how a resistance of 25-ohms or less provides additional safety. Unless you are able to get the resistance of a ground rod to around 2 ohms or less it will not trip a 20 amp breaker with a 120 volt fault to the ground rod in a reasonable amount of time. In the event of lightning, the voltage is so high that a resistance difference of a few (or a few hundred) ohms would be negligible. The code making panels understand that requiring a low resistance on ground rods would serve no purpose so they do not require it.

Just use Ohm's law. If we apply 120 volts to a 25 ohm resistance there will be 4.8 amps flowing, so you will not trip a 20-amp breaker.
Lower the resistance by half to 10 ohms and there will be 12-amps flowing, so still no breaker trip.

Lower the resistance to 5 ohms and you will see 24 amps flowing which MAY eventually trip a 20-amp breaker, but I wouldn't want to hold my breath waiting for it!

Ground rods serve a purpose, but it is NOT tripping overcurrent devices!

If you have 1,000,000 volts in a lightning strike and a 25-ohm resistance you would measure 40,000 amps. If you had a resistance of 100 ohms you would only measure 10,000 amps. I don't see where that would make a big difference in the trip time of a breaker.

Grounding does what it does, it is not magic. Requiring low resistance on a ground rod is a waste of time and money and does not add to the safety of an installation.
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Electrical Ground is not about reaching a particular value, its about getting an appropriate reference with respect to the voltage source. Take for example, if on an air borne Airplane, if I measure the electrical ground resistance (referenced wrt to body of the plane), and if it is further away from zero, the more is the concern of safety.

Typically the sheer volume of structure make it a better ground than electrical ground if both are not bonded together. Here is clip that sites the importance of having a building grounding resistance as close as electrical grounding resistance:
ground.jpg
 
Last edited:
bullheimer said:
perfect for my question and i believe what you are saying is that i can do this:

i have two ground rods i want to install on the way to the same end of the house the gas is at. so i may use bare #4 (200A service) to go to my two ground rods, then go to the gas pipe. correct? at least that what i think you said. (also for above post, couldn't he use the water pipe w/in five feet AS the second grounding electrode if he only wants to pound in one?)
Click to expand...

Where are you 'bonding' the gas lines?
 
25 Ohms

25 Ohms

infinity said:
The NEC requires two rods unless you can prove that one rod has a resistance of 25 ohms or less.
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I recently had a discussion with an L&I electrical inspector from WA in Olympia who said he had never heard of anyone ever using less than one ground rod in his 35 years as an inspector. I so wanted to invite him to my two houses and as many neighbor's houses as I had discussed this with and show him some of those "rare" homes. I didn't want to delve into using a fall of potential or clamp on ground tester since he was insistent on proving my method wrong...I let him have that one since he likely would be approving the work. Ya gotta know when to pick your fights.
 
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