Agreed. Concentrate on good and reliable bonding.
Purpose of ground rod
- Thread starter Rjryan
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kwired
Electron manager
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- NE Nebraska
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- EC
If you have qualifying water pipe structural steel or a CEE there is still some benefit. Two rods however is likely useless most the time.
jaggedben
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The grounded conductor (the neutral, almost always) is so called because it is grounded on the utility's network as well as on the premises. A second grounded conductor that is out of the reach of ordinary people would be redundant. (Arguably the EGC is redundant inside the home, but it's a different situation with respect to occupant safety.)
On a typical residential transformer you have several homes connected to it. It's a good thing that the neutral is grounded at all of the homes and not just the transformer. Otherwise if the neutral loses its connection to ground at the transformer, or gets broken anywhere in between, then the occupants in the homes will experience voltages between the ground and bonded metal parts, possibly enough to shock and hurt them.
In some other countries they do things a bit differently but they need residual current devices (GFCIs, essentially) on everything. And they still need electrodes.
petersonra
Senior Member
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- Northern illinois
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- engineer
What is the benefit of a water pipe electrode? You have to connect it inside the house. That means whatever lightning might be shunted to ground (a dubious idea IMO), is brought from the outside of the house to the inside where it can do more damage.
kwired
Electron manager
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- NE Nebraska
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- EC
Ground electrodes won't prevent damage to a direct lightning strike period.
They may however reduce the effects of an incoming transient but this be transients from POCO switching operations and such, or surge that might occur when a transmission line accidentally dropping on a local distribution line as well as lightning incidents that don't occur directly at the building.
Transmission line dropping on a local line still often causes damage within a mile or two of where said incident takes place though, sort of depends on how quickly overcurrent protection responds or even if it has a recloser involved and tries to energize again.
- Location
- Illinois
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- retired electrician
The main benefit of a connection to a common underground metal water piping system is that is provides a solid metallic path that will prevent damage when the service neutral is lost.
petersonra
Senior Member
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- Northern illinois
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- engineer
if that is what it is for why does the code not say so?
xformer
Senior Member
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- Dallas, Tx
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- Master Electrician
90.1(A)
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I guess sorta, but that is not what the GES is for....seems like then it's just a ticking time bomb waiting for someone to work in the piping and THEN fry everything and probably get shocked in the process. If the code writers think a redundant neutral conductor is prudent then maybe they should require one.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
I think you missed the point. The code gives specific reasons for grounding and this is not one of them.90.1(A)
xformer
Senior Member
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- Dallas, Tx
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- Master Electrician
Just when I thought, I knew something.
hillbilly1
Senior Member
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- North Georgia mountains
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- Owner/electrical contractor
I had a job where the metal conduit ground worshippers used a pvc nipple from the panel inside a gas station to the metal wireway outside. Hundreds of feet of rigid buried to the pumps. Customer complained about getting shocked from the door handles. Found a #12 stripped back, and laying against the wireway. Even with all that rigid buried, the 20 amp breaker only had about 3 amps on it. It was amazing nobody got electrocuted at the pumps!
kwired
Electron manager
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- NE Nebraska
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- EC
Code doesn't state the why for majority of it's content.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
Yet in this case it does. Curious.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
What you quoted from NEC earlier doesn't outright say why grounding is required.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
It actually does, and the verbiage is quite clear about that. There may be other things going on there but what it says is pretty clearly the primary reasons for grounding.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I can agree the primary reasons are not quite what some maybe expect it to be. Mostly for an earth reference and stabilizing voltage to earth when a high voltage incident occurs.
opes at askronald
Member
The purpose of the building ground rod at the service is to help keep the building at equal potential with earth and does not protect against fault currents or lightning strikes. NEC requires a maximum of #4 CU ground conductor between the service equipment and the ground rod. Lightning protection conductors are braided by design and building wire is not. There is a reason. To protect a building [ not electronics or equipment ] from lightning requires a combination of lightning protection system is required per LPI and NFPA 78.
The other issue is 25OHMS to ground at your single ground rod to meet code. Try proving you comply. I just use two ground rods and never bother with the 25ohms criteria.
romex jockey
Senior Member
- Location
- Vermont
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- electrician
being a good neighbor.....? ~RJ~
I worked in power production in the Air Force ~5 decades ago and I cannot remember getting that low of an impedance to earth. I also was detailed to Fire Alarm Telegraph System maintenance and those clockwork driven numerical telegraph transmitters had to be able to transmit via ground return if there was an open anywhere on it's single wire looped fire alarm box circuit.
I was given about the niftiest little drill rig to get the rods in and I've never seen anything like it since. It pulled out from a compartment on the side of the add on body of a pickup. I felt like a dunce, and still do when I tell about it, but I put in 3 or 4 Rods with stacked 10 foot sections until I got some of the boxes to signal via ground return. Then it donned on me that the open in the ground might be at the fire alarm office. I talked the Sergeant into letting me test the office grounding and it was over 100 Ohms to earth. That alarm office was built during world war 2 and the grounding for it was all galvanized steel. In the ensuing 30 years it had corroded open. It was under constant assault by AV Gas followed by JP-4 and it's predecessors because were they parked fuel trucks was just on the other side of the perimeter fence. The office still had it's required 100 foot clearance from all other structures and vehicles but the ground was saturated with fuel from decades of spills. They let me install the new grounding system because I really wanted to get those dammed street fire alarm stations fully functional again. A heavy equipment operator exposed the top of the footer all the way around the building. The spoil pile stank terribly of spilled fuel. There was very little left of the original Ground rods at each corner of the building. They looked to be about the size of a #10 wire run vertically in the soil. Whatever was originally used to bond the rods together was gone completely. Once I got the use of a utility pole hole borer from the communications squadron it was really easy to get holes down to 30 feet from the top of the footer which was ~10 feet below ground level. I'd have gone to 40 but they didn't have that many extensions for the augur shaft. I personally filled each of the bores with Bentonite which had to be mixed to the consistency of putty before pouring it into the holes. I did get all 40 foot of rod down in 2 or 3 of the bored holes so that the top of the coupled rod was 10 feet below ground at the top of the footer. That made the drilled end of the rod 40 or 50 foot deep. I bonded the rods to the ground ring by exothermic welding. I put in a Ground Ring because the bonding conductor for the rods was going to be 10 foot below ground level so I got permission to use the large conductor. It ended up being 2/0 because the supply folks had enough left over from some other job. The Ground Ring had a foot of Bentonite in all directions around it. I know because I tamped it. The last touch I think was a good idea and entirely mine. I got the guys from base engineering to show me how to prepare the basement walls and once I had wire brushed it all down they sprayed it with HOT tar. They said that they used the stuff to repair roads and roofs. I had seen them patching roads with it which is were I got the idea. The wire guys that had to work in that basement at times told me they really appreciated my "drying it in" for them.
When we were finished we did a 4 pole fall of potential ground impedance test on the system. We did get it down to ~3 Oms but I've never heard of getting a Grounding Electrode System below a single ohm.
OK I'll admit it. I was proud of the way it turned out. But I still feel dumb about not suspecting the grounding at the fire alarm office until after I put in my 4th 30 foot long ground rod to get the ground return to work from an alarm station.
Tom Horne
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