In some locations, electricians choose to install more than 1 rod for their grounding electrode system. This is the main grounding electrode since water pipe, building steel, nor concrete encased is not available on an existing building. This is sometimes done when trying to achieve 25 ohms or less. What size of grounding electrode conductor must be used when multiple rods are used? Does NEC 250.66 (A) still apply?
Multiple ground electrodes
- Thread starter mike w
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Multiple ground electrodes
The maximum size required to a grounding rod or rods, is #6 cu.
The maximum size required to a grounding rod or rods, is #6 cu.
bphgravity
Senior Member
- Location
- Florida
Re: Multiple ground electrodes
Just for clarification, the conductor from the service to the first rod is the grounding electrode conductor. The conductor from the first rod to any additonal rods or electrodes is a bonding jumper. Unless you leave the GEC in one continuous length between electrodes. Then I guess the whole length is a GEC.
In any case, #6 AWG is the max for any installed configuration.
Just for clarification, the conductor from the service to the first rod is the grounding electrode conductor. The conductor from the first rod to any additonal rods or electrodes is a bonding jumper. Unless you leave the GEC in one continuous length between electrodes. Then I guess the whole length is a GEC.
In any case, #6 AWG is the max for any installed configuration.
electricmanscott
Senior Member
- Location
- Boston, MA
- Occupation
- Massachusetts Master Electrician, one man show.
Re: Multiple ground electrodes
Generally it is not a "choice" to install two rods.
Generally it is not a "choice" to install two rods.
southernboys
Senior Member
Re: Multiple ground electrodes
Heres a question Ive got that Ive never fully understood when I see a #6 max. Here you better run a #4 egc out of your power pack to two ground rods continuious. This is then tied into your nearest cold water ground. We also bond the water heater with a #4 jumper from cold to hot pipe. Now if I understand the nec only requires a #6? Is this correct?
Heres a question Ive got that Ive never fully understood when I see a #6 max. Here you better run a #4 egc out of your power pack to two ground rods continuious. This is then tied into your nearest cold water ground. We also bond the water heater with a #4 jumper from cold to hot pipe. Now if I understand the nec only requires a #6? Is this correct?
southernboys
Senior Member
Re: Multiple ground electrodes
Correction to my last post. There are two #4s one to the ground rods one to the cold water pipe
Correction to my last post. There are two #4s one to the ground rods one to the cold water pipe
Re: Multiple ground electrodes
What size service determines your jumper at the water heater. If you have a 100A service #8 GEC, 200A service #4 GEC
T250.66
[ February 24, 2006, 07:00 PM: Message edited by: tshea ]
#4 because it is not susceptible to physical damage. :roll: (inspector insisted a #6 be changed because a lawn mower could cut the GEC. I said probably true but I think the lawn mower will hit the ground rod first and that will stop the engine cold thus protecting the wire. In the days before an 8' rod was required to be driven below the surface.)
What size service determines your jumper at the water heater. If you have a 100A service #8 GEC, 200A service #4 GEC
T250.66
[ February 24, 2006, 07:00 PM: Message edited by: tshea ]
allenwayne
Senior Member
Re: Multiple ground electrodes
I also use # 4 to avoid having to protect it.As far as # of ground rods certain jurisdictions require 2 or you have to show resistance of the groung rod to the inspector.I would rather sink the second rod than have to be there for each and every inspection they do.
I also use # 4 to avoid having to protect it.As far as # of ground rods certain jurisdictions require 2 or you have to show resistance of the groung rod to the inspector.I would rather sink the second rod than have to be there for each and every inspection they do.
Re: Multiple ground electrodes
at a california shop I worked for their standard was using armored #6 with 2 ground rod clamps designed for the armored cable. This was really nice for 2 reasons, no digging (attach to wall) and it felt good to know it wouldn't get damaged half as easily.
at a california shop I worked for their standard was using armored #6 with 2 ground rod clamps designed for the armored cable. This was really nice for 2 reasons, no digging (attach to wall) and it felt good to know it wouldn't get damaged half as easily.
Minuteman
Senior Member
- Location
- The Sooner Nation
Re: Multiple ground electrodes
250.66(B) 2002 Connections made to Concrete-Encased Electrodes. Where the grounding electrode conductor is connected to a concrete-encased electrode as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire
Here Supplementary Grounding Electrodes 250.54 are REQUIRED and we follow 250.66 up to a #4 and run unbroken from the panel to the CEE and to the SGE. Also, the connection to the ECC has be accessible. We us a single gang plaster wring or a LV1, and a blank plate.
250.66(B) 2002 Connections made to Concrete-Encased Electrodes. Where the grounding electrode conductor is connected to a concrete-encased electrode as permitted in 250.52(A)(3), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire
Here Supplementary Grounding Electrodes 250.54 are REQUIRED and we follow 250.66 up to a #4 and run unbroken from the panel to the CEE and to the SGE. Also, the connection to the ECC has be accessible. We us a single gang plaster wring or a LV1, and a blank plate.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Multiple ground electrodes
Didn't you mean supplemental grounding electrode? Also I would add that only GEC's are required by the NEC to be run unbroken. Supplemental electrodes are connected by bonding jumpers and are not required to be continuous back to the service grounded conductor. Only an underground metal water pipe is required to have a supplemental electrode by the NEC, a CEE would not require one.
Minuteman
Senior Member
- Location
- The Sooner Nation
Re: Multiple ground electrodes
I don't know to much about things that are suppose to be mental.
I was just commenting that local code require two grounding source. Plumbers use mostly plastic now. So either we install a CEE & rod or 2 rods.
[ February 27, 2006, 07:48 AM: Message edited by: Minuteman ]
I don't know to much about things that are suppose to be mental.
I was just commenting that local code require two grounding source. Plumbers use mostly plastic now. So either we install a CEE & rod or 2 rods.
[ February 27, 2006, 07:48 AM: Message edited by: Minuteman ]
rick hart
Senior Member
- Location
- Dallas Texas
Re: Multiple ground electrodes
This might be better off in the Engineering section and I hope this does not sound like a DIY on the loose....
Getting away from the minimum code requirement of #6 to a driven rod and looking at making a very low impedance path to ground, what would be considered a more effective (cost vs. performance) driven ground electrode system:
1. A single driven rod and #6 (existing)
2. Two driven rods and #4 12 feet apart
3. Multiple driven rods, X feet apart in what sort of configuration- square box, straight line, Y- with a welded 3/0.
The building has a listed lightning protection system but the bond to the service entrance connects to a #6 existing driven rod. The foundation is a poured slab with plastic sheet vapor barrier and PVC water connection to the meter. The SE GEC (3/0) connects to the water system- 1200A service, TVSS on main - by running >100 feet in the attic. Lightning damage is a recurring problem and I'm thinking that the existing GEC has way too much impedance to carry the shunted voltage to ground, forcing the voltage to seek ground wherever it can find it.
I know driven rods are not the best grounds but that appears all the alternatives I have.
[ February 27, 2006, 09:40 AM: Message edited by: rick hart ]
This might be better off in the Engineering section and I hope this does not sound like a DIY on the loose....
Getting away from the minimum code requirement of #6 to a driven rod and looking at making a very low impedance path to ground, what would be considered a more effective (cost vs. performance) driven ground electrode system:
1. A single driven rod and #6 (existing)
2. Two driven rods and #4 12 feet apart
3. Multiple driven rods, X feet apart in what sort of configuration- square box, straight line, Y- with a welded 3/0.
The building has a listed lightning protection system but the bond to the service entrance connects to a #6 existing driven rod. The foundation is a poured slab with plastic sheet vapor barrier and PVC water connection to the meter. The SE GEC (3/0) connects to the water system- 1200A service, TVSS on main - by running >100 feet in the attic. Lightning damage is a recurring problem and I'm thinking that the existing GEC has way too much impedance to carry the shunted voltage to ground, forcing the voltage to seek ground wherever it can find it.
I know driven rods are not the best grounds but that appears all the alternatives I have.
[ February 27, 2006, 09:40 AM: Message edited by: rick hart ]
bphgravity
Senior Member
- Location
- Florida
Re: Multiple ground electrodes
If you have 3/0 copper, even at 100', it is going to have way less impedance if connected propoperly, than any grounding system you try to create with rods.
Lightning damage is usually a bonding problem and not a grounding problem.
What damage from lightning are you referring to? Is the structure receiving damage or is the electrical equipment.
If you have 3/0 copper, even at 100', it is going to have way less impedance if connected propoperly, than any grounding system you try to create with rods.
Lightning damage is usually a bonding problem and not a grounding problem.
What damage from lightning are you referring to? Is the structure receiving damage or is the electrical equipment.
rick hart
Senior Member
- Location
- Dallas Texas
Re: Multiple ground electrodes
Electrical appliances are being damaged- electronics mostly- no visible structural damage.
The reason I am looking at driven rods isn't the size of the GEC conductor but what the 3/0 connects to. I believe that there is not a very good connection between the water pipe and Earth because of the limited plumbing and plastic vapor barrier. The lightning system is obviously doing its job of protecting the structure and is bonded at the ground rod #6 bonding jumper back to the service enrance.
If there is not a low impedance path to absorb the energy, a surge will back into or induct other paths to find ground. I'm thinking that if the electrode itself is not performing, the 3/0 is acting like a broadcast antenna when the high current is shunted to ground by the TVSS.
That's the latest straw I'm grabbing at. Pretty far out there, huh?
Electrical appliances are being damaged- electronics mostly- no visible structural damage.
The reason I am looking at driven rods isn't the size of the GEC conductor but what the 3/0 connects to. I believe that there is not a very good connection between the water pipe and Earth because of the limited plumbing and plastic vapor barrier. The lightning system is obviously doing its job of protecting the structure and is bonded at the ground rod #6 bonding jumper back to the service enrance.
If there is not a low impedance path to absorb the energy, a surge will back into or induct other paths to find ground. I'm thinking that if the electrode itself is not performing, the 3/0 is acting like a broadcast antenna when the high current is shunted to ground by the TVSS.
That's the latest straw I'm grabbing at. Pretty far out there, huh?
pierre
Senior Member
- Location
- Westchester County, New York
Re: Multiple ground electrodes
"I'm thinking that if the electrode itself is not performing, the 3/0 is acting like a broadcast antenna when the high current is shunted to ground by the TVSS."
The TVSS is not shunting current to ground.
"I'm thinking that if the electrode itself is not performing, the 3/0 is acting like a broadcast antenna when the high current is shunted to ground by the TVSS."
The TVSS is not shunting current to ground.
rick hart
Senior Member
- Location
- Dallas Texas
Re: Multiple ground electrodes
OK, Pierre.
Voltage is being shunted but absolutley NO current allowed!
OK, Pierre.
Voltage is being shunted but absolutley NO current allowed!
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