two ground rods

[radiopet]

Re: two ground rods

I guess I am left asking this question from the original post:

1.) Did the inspector ACTUALLY read the ohms to ground to place the comment on the rods..even if he is wrong about the placement.

2.) Did you actually do the tests and read over 25 Ohms in the first place to add the additional Gnd Rod?


I understand where it is going just not sure if it was done for a reason or because of a reading.

I can't remember a single time in my electrical career that I had a inspector read the resistance to ground and tell me the ohms were over 25....so I was curious if you actually took the reading or did it to apply some additional theory.

 

[petersonra]

Re: two ground rods

How would he go about measuring the ground resistance w/o some specialized equipment?

Its not as if you can stick one probe of an ohmmeter in the ground and touch the other to the ground rod to make this test.

 

[radiopet]

Re: two ground rods

Thus my question...who required 2 Rods and if they did it had to be someone other than the inspector in question because the inspector would have said something about the 2 rods and the distances well before that...

So I again ask....what was the reason for the 2 rods unless testing was done to determine a higher than 25 ohms reading?

 

[jtester]

Re: two ground rods

It would seem reasonable for the installer to prove he had 25 ohms or less. The inspector would just ask for the test.
Here in Southern New Mexico, 25 ohms is almost always impossible. We don't even try, we just drive a second rod.
Jim T

 

[wirenut1980]

Re: two ground rods

Even if 25 ohms of resistance is easily obtained with 1 ground rod, most times it is still cheaper to just drive another ground rod instead of taking the time and getting the equipment to do a proper GES resistance test. Or it could be local conditions like jtester said.

 

[iwire]

Re: two ground rods

Originally posted by radiopet:
So I again ask....what was the reason for the 2 rods unless testing was done to determine a higher than 25 ohms reading?

The NEC requires 25 ohms or less or a second rod.

The inspector could do the test or he could ask the EC to perform the test while he is present.

Your inspectors may have been ignoring the NEC.

250.56 Resistance of Rod, Pipe, and Plate Electrodes.

A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(2) through (A)(7). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.

 

[radiopet]

Re: two ground rods

Bob,

I am aware of the code requirements on that issue regarding ground rods and spacing and ohms and so on but I was more concerned with the person that posted it...

1.) Did they do the tests to determine it needed more than one.

2.) Did the inspector do the tests and determine it as well and is it the same inspector who read the code incorrectly in regards to the 6 foot Min. requirement.

Basically, I was saying that in my 16 years of doing electrical I NEVER ( and in 3 different counties ) have never had a inspector check the ground rod or so on.....

But I was mainly wondering in regards to the person who posted the message in regards to his issue with the inspector and the spacing of his ground rods....did he do it because of a reading or a directive from a inspector.

 

[don_resqcapt19]

Re: two ground rods

radiopet,
I don't think that it is the inspectors job to prove that a single rod meets the 25 ohm rule. If the inspector questions it, it is the contractors job to either prove compliance or add the second rod. Proving compliance will often be more costly than adding the second rod.
Don

 

[relbas]

Re: two ground rods

Can you explain how you measure 25 oms on the ground rod.

 

[tshea]

Re: two ground rods

Here in WI we are required to drive the 2nd ground rod. COMM16 (State Code)
We do not have to do a ground rod resistance check, just install rod #2. We are done!

When opportunity arises we prefer the UFER. Low cost, NO maintenace.

 

[charlie b]

Re: two ground rods

Originally posted by relbas: Can you explain how you measure 25 oms on the ground rod.

This has been discussed in several threads on this forum. Here's one.
Here's another.

 

[brian john]

Re: two ground rods

And then if you do have the 25 ohms on the day of installation what happens over the years. Deterioration.

 

[izak]

Re: two ground rods

I was on a job where the specs called for 'less that one ohm to ground'

all the underground duct banks that we laid had 4/0 copper laid on top of the concrete, (and there was probably close to a mile of that)
plus a ground grid that went ALLL the way around the main building and all smaller buildings with 4/0 copper and 10 ft copperweld rods every 25 feet
and allof it cadwelded together...

i never saw the test but,
here in this rocky soil, ill bet we were lucky to get 25 ohms...