Ground rods

[Pierre C Belarge]

Why would you need a larger than #6 wire to a ground rod?

If I mentioned or inferred that the conductor to the rod is required to be any particular size, that was not my intention.

There are specifications written for particular jobs that require as a spec larger conductors terminated to ground rods. I have actually seen 500 kcmil terminated to rods. That is what I was alluding to.

 

[mdshunk]

There are specifications written for particular jobs that require as a spec larger conductors terminated to ground rods. I have actually seen 500 kcmil terminated to rods. That is what I was alluding to.

Come to think of it, I've seen rods installed at intervals on ground rings. I think a ground ring is often around #2 copper. I'm not sure what the addition of rods does, but I guess it helps.

 

[ultramegabob]

if you use a rotary hammer with a ground rod cup, you dont mushroom the head, if you drive many groundrods, a rotary hammer pays for itself pretty quick when you take in consideration the time and effort it takes to drive one with a hammer....

 

[LarryFine]

http://www.erico.com/products/EK16EK17.asp

Interesting the way they tout the "one-clamp-fits-all" benefits, then you have to choose between perpendicular and parallel models.

 

[nakulak]

we did a job and the gov spec'd clamps similar to the top and bottom connectors shown in this page:

http://www.harger.com/products/grdcmp/grdeleac/grc/grc.cfm

we were using mostly 2/0. The ones at the bottome were spec'd so that someone could take the grounds loose and measure grounding resistance. I like them both, and I also like the fact that there's more surface area in contact with the ground rods than a normal acorn (which I assume is why they are listed for class 2 lightning protection). Seems to me that if ground rods are really for lightning protection, why aren't all the clamps designed larger for more ampacity ?

 

[tom baker]

Its not a state or NEC rule. Its Washingtons explanation of how their inspectors enforce this.

 

[mistermudd]

Our jurisdiction now allows us to cut ground rods.......

If you:
forget to put the ground rod clamp on the rod before driving it and mushroom the rod?s head, you may cut
no more than 1? off the top of the rod using an angled cut (i.e. 20​

​

? to 45? across the rod) if you leave the
cut piece attached (e.g. tape or other method) to the grounding electrode conductor just above the
connection to the electrode. The inspector will use the cut piece to determine if the rod is full length.

For my Washington gurus: If this was always a rule, then excuse me for missing it:grin: ​

I would be interested where this piece of information came from. Do you believe it is a local or statewide rule???

I am in WA State & cutting ground rods is a huge no-no. Our Electrical Currents newsletter which started about ten years ago addresses this issue several times & there is no WAC law stating it is okay to cut rods for any reason. In fact it is considered a serious violation.

If you are doing work in Washington State DO NOT cut the ground rods, if there is a situation where you are having trouble installing rods to the NEC requirements you should get a hold of the inspector in the area and let them know what is going on & work out a solution.

 

[frizbeedog]

To a ground rod?? Why?

To sustain the damge from a strike perhaps?

 

[jghrist]

To a ground rod?? Why?

NFPA 780, Standard for the Installation of Lightning Protection Systems, requires main conductors (incl. down conductors) to be 57.4 MCM (between #2 & #3) for buildings 75 ft high and lower and 115 MCM (between #1/0 and #2/0) for buildings higher than 75 ft.

 

[mistermudd]

I stand corrected, you must have received the latest WA ST newsletter. It was in my e-mail today & there it was. After I had posted my prior comment, I thought I could vaguely remember something about cutting off a rod and leaving the top as evidence from about 15 years ago obviously it is still on the books.

 

[Dennis Alwon]

NFPA 780, Standard for the Installation of Lightning Protection Systems, requires main conductors (incl. down conductors) to be 57.4 MCM (between #2 & #3) for buildings 75 ft high and lower and 115 MCM (between #1/0 and #2/0) for buildings higher than 75 ft.

And what sense does this make if the rod is only as good as a #6. Does NFPA say the #2 is to be connected to a ground rod or a ground ring or another type of electrode.

 

[frizbeedog]

And what sense does this make if the rod is only as good as a #6. Does NFPA say the #2 is to be connected to a ground rod or a ground ring or another type of electrode.

Help, get an engineer over here. It is my understanding that lighting protection systems are engineered. I'm glad you keep asking that question Dennis, because now I really want to know. I can wrap my mind around the larger conductor as it relates to being able to withstand the strike but the rod seems to be the weak link based on how we understand it's use. My new research project.

 

[frizbeedog]

And what sense does this make if the rod is only as good as a #6. Does NFPA say the #2 is to be connected to a ground rod or a ground ring or another type of electrode.

Try this site for lightnig protection info

 

[jghrist]

And what sense does this make if the rod is only as good as a #6. Does NFPA say the #2 is to be connected to a ground rod or a ground ring or another type of electrode.

I'm not sure what you mean by the rod only being as good as a #6. NFPA allows different types of grounding electrodes.

The main concern with lightning is inductance of the path because of the high frequency of lightning (actually high rate of rise or di/dt). Lightning protection is more of an art and is based on experience more than analysis. Experience that goes back to Ben Franklin's day. I'm sure that's why you see oddball conductor sizing and stranding used for lightning protection systems.

 

[Dennis Alwon]

I'm not sure what you mean by the rod only being as good as a #6. NFPA allows different types of grounding electrodes.

The main concern with lightning is inductance of the path because of the high frequency of lightning (actually high rate of rise or di/dt). Lightning protection is more of an art and is based on experience more than analysis. Experience that goes back to Ben Franklin's day. I'm sure that's why you see oddball conductor sizing and stranding used for lightning protection systems.

I thought we were talking about ground rods. Certainly there are other electrodes that would benefit from a larger conductor but not an 8' ground rod. otherwise, I wouldn't think the NEC would say that a #6 is all that is necessary

 

[resistance]

Its not a state or NEC rule. Its Washingtons explanation of how their inspectors enforce this.

Interesting!

 

[brantmacga]

hmm. i haven't bought a ground rod in almost two years now that wasn't tapered on both ends. I thought everyone was making them like that now. Those tapered ends don't seem to mushroom like the flat ends did; and if they do, the acorn clamp will still clear.

 

[resistance]

I would be interested where this piece of information came from. Do you believe it is a local or statewide rule???

I am in WA State & cutting ground rods is a huge no-no. Our Electrical Currents newsletter which started about ten years ago addresses this issue several times & there is no WAC law stating it is okay to cut rods for any reason. In fact it is considered a serious violation.

If you are doing work in Washington State DO NOT cut the ground rods, if there is a situation where you are having trouble installing rods to the NEC requirements you should get a hold of the inspector in the area and let them know what is going on & work out a solution.

I'm surprised you didn't get the Electrical Currents for April--seeing that you are an electrical inspector. Check Vol 11 Number 4 April 2008

If they did not post it on LNI's page, then check your mail, you should have this.

 

[Commelec]

didn't anyone in this state hear of ground clamps that are 2-piece ? (or the cad-weld one-shots ?)

I use Cald-Weld or Ultra-Weld one shots for both single and multiple conductors. I typically use a Cald-Weld Kit with molds and various weld metals but I've found it easier to work with the one-shots as they provide a mold, ready to go with any accessories needed to do the shot except for ignition source and the weld-metal is included. All you have to do is clean the rod, conductor you're welding, heat and dry with a torch, set up and fire. When you're done, the ceramic "one-shot" mold can be knocked off with a hammer and you're done. No mold to clean up or wait forever to cool down and they don't cost much more than your weld metals in some cases, $10-$15 max.

 

[Commelec]

Come to think of it, I've seen rods installed at intervals on ground rings. I think a ground ring is often around #2 copper. I'm not sure what the addition of rods does, but I guess it helps.

Typically high risk sites, such as radio towers, etc... have a ring (Minimum #2 AWG or equivalent Copper) that is burried underground around both the building with 1 ground rod and then add as necessary around the ring per your ground (Megger) resistance rating and or place radials off each corner at 50' to 75' minimums. There are basic guidlines and studies based off your soild samples and resistivity. These standards are all based off of R-56 Site Grounding and Lightining Protection and years of experience frying equipment! :grin: