grounding electrodes

[LMaloney]

I am currently thinking of proposing an ammendment to have electrical contractors keep grounding electrodes 2' off of the structure. My concern is the soil that is used to fill around the foundation as far as resistance to ground. My other concern is the moisture change since typically it would be partially protected by the drip edge and in some cases drain tiles. Does this make sence based on the fact that the NEC doesn't really address this unless classified as a lightning protection system? I know a lot of inspectors in my area enforce this, but we always try to make sure we back it up with code. Thanks

 

[infinity]

Re: grounding electrodes

I know a lot of inspectors in my area enforce this, but we always try to make sure we back it up with code.

A proposal might be in order since you say that inspectors are enforcing language that isn't in the code book. I for one would protest any such interpretation that isn't explicitly written in the text.

 

[charlie b]

Re: grounding electrodes

I have no problem with the concept. But you need to put it in your back pocket for a couple of years. The deadline for submitting code changes for the 2008 cycle has passed. They probably won't open the door for 2011 submittals until sometime in late 2007 or early 2008.

 

[petersonra]

Re: grounding electrodes

i think this is a dumb idea.

if the rod is located near the wall it is relatively well protected from damage.

if it is 2 feet away, it would need to be buried.

besides, most new homes will not even have a ground rod, but will use the rebar in the foundation as the GE.

 

[allenwayne]

Re: grounding electrodes

Bob that depends on the area some require both

 

[electricmanscott]

Re: grounding electrodes

Originally posted by petersonra:


if the rod is located near the wall it is relatively well protected from damage.

I don't see how you could use this as an argument to not need protection from damage.

As for moisture the rod is supposed to be below the pemanent moisture level so this should be a non issue.

 

[infinity]

Re: grounding electrodes

Bob that depends on the area some require both

Where do they require both? Is that a local requirement?

 

[mdshunk]

Re: grounding electrodes

Originally posted by infinity:

Bob that depends on the area some require both

Where do they require both? Is that a local requirement?

I work in 5 POCO areas. 3 of the 5 require the ground rods, regardless of code and regardless of what other grounding electrodes I'm using. I don't have a choice if I want them to tap me up.

 

[websparky]

Re: grounding electrodes

Bob,

if the rod is located near the wall it is relatively well protected from damage.

if it is 2 feet away, it would need to be buried.

besides, most new homes will not even have a ground rod, but will use the rebar in the foundation as the GE.

and infinity,


I disagree.
Ground rods will always be needed in some installs. For instance, a pole barn or a building constructed of post and beam that do not have a city water supply. The only types of electrodes possible are ground ring, rod or pipe and plate.

Below are the requirements for rods. Like Scott said, the "permanent moisture level" is an issue. Also, the rod must be burried it's entire 8' length.

250.53
(A) Rod, Pipe, and Plate Electrodes. Where practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.

(G) Rod and Pipe Electrodes. The electrode shall be installed such that at least 2.44 m (8 ft) of length is in contact with the soil.......

[ November 17, 2005, 09:53 PM: Message edited by: websparky ]

 

[infinity]

Re: grounding electrodes

and infinity,


I disagree.
Ground rods will always be needed in some installs. For instance, a pole barn or a building constructed of post and beam that do not have a city water supply. The only types of electrodes possible are ground ring, rod or pipe and plate.

The point I was trying to make is that ground rods are not required if you used a Ufer ground in the footing like Bob Peterson stated. Allen stated that some places require both the Ufer and grounds rods. This is not supported by the NEC. So I was wondering if this were a local requirement.


Trevor

 

[pierre]

Re: grounding electrodes

The contact resistance of most ground rods is quite high. I still say that adding the second ground rod is not effective enough to warrant trying to meet the 25 ohms to ground. I have tested many installations with two ground rods, and they measure in the neighborhood of 70-200 ohms - thats two groundrods. So please tell me why we need two ground rods???????????????? I do not see the reason.

As far as any POCO requiring ground rods if there is a better installed GEC such as the footing, that is purely from ignorance. As a matter of fact, I am working with the local POCO here on helping them to change that same requirement here. I believe that sometime next year that requirement will change.

Oh yeah... why are we trying to meet 25 ohms to ground?

BTW- as much as I think that a second ground rod is the largest waste of time and money, I still follow the code requirement. Hopefully we can see some relief from this in the NEC sometime in the next few cycles.

[ November 18, 2005, 06:47 AM: Message edited by: pierre ]

 

[allenwayne]

Re: grounding electrodes

MD The city of tampa requires both a uffer tag and a ground rod.This is a local requirement.

 

[allenwayne]

Re: grounding electrodes

Where we are required to install a ground rod the inspectors want it as close to the building as possible to prevent grading damamge and would like us to mark in the meter distance back of rod location.Not required but as a curtosy we do it.

 

[George Stolz]

Re: grounding electrodes

the inspectors...would like us to mark in the meter distance back of rod location.

To which I would reply, "I would like it if you gave me a $20 tip for every house of mine you inspect." That is the G-rated reply, of the four that came up.

Why? Who? What? That's got to be the dumbest (or close to it) thing I've heard this morning. Is Indiana Jones going to need to find it? You draw them a map?!? That's nuts.

 

[iwire]

Re: grounding electrodes

Originally posted by georgestolz:
Is Indiana Jones going to need to find it?

See the latest major motion picture release.

Indiana Jones The Search for 25 Ohms or Less

 

[bphgravity]

Re: grounding electrodes

You would think one of the fine gentlemen that attended Mr. Holt's recent grounding vs bonding seminar would divulge the information on the origin of the magical "25 ohm" requirement.

 

[allenwayne]

Re: grounding electrodes

It`s just called courtesy just plain old courtesy.One hand washes the other and they both wash the back.Oh believe me there are certain inspectors I`ll watch them dig to find the steel ufer or ground rod (they are requied to check these on finals)
But the others I tell them 11 R B is 11 ft rt side back.I also say I don`t do this for all inspectors but you always work with me so here is a little help

 

[charlie b]

Re: grounding electrodes

Originally posted by bphgravity: You would think one of the fine gentlemen that attended Mr. Holt's recent grounding vs bonding seminar would divulge the information on the origin of the magical "25 ohm" requirement.

From what I remember, it was not a matter of "This is why we picked 25 ohms." It was more along the lines of, "We installed a ground rod of XXX material and of YYY length, in dirt with a thermal resistivity value of ZZZ Degree-Centimeters per Watt, and the resulting ground resistance measurement was 25 ohms." In other words, it was a description of an experiment, as opposed to being a design process.

 

[pierre]

Re: grounding electrodes

Bob
I heard the reviews for the Indiana Jones searches for the elusive 25 Ohms to ground was a flop.... because there is no ending

 

[charlie b]

Re: grounding electrodes

Originally posted by pierre:I have tested many installations with two ground rods, and they measure in the neighborhood of 70-200 ohms ? that's two ground rods. So please tell me why we need two ground rods???????????????? I do not see the reason.

Because the best available alternative is more, not fewer. I mean, which of the following two proposed revisions is more likely to be given serious consideration by the code committees?
</font>

• <font size="2" face="Verdana, Helvetica, sans-serif">Proposed Revision 1: Pound one ground rod and call it a day,</font>

<font size="2" face="Verdana, Helvetica, sans-serif">or
</font>

• <font size="2" face="Verdana, Helvetica, sans-serif">Proposed Revision 2: Keep pounding ground rods until you get to 25 ohms.</font>

<font size="2" face="Verdana, Helvetica, sans-serif">Whatever else might be said about this subject, this is one true-life example of "two is better than one." That is not debatable. The thing that is debatable is whether the cost of the "two" is worth the amount of "is better" that you get for your money.