Grounding electrode

[Billy D]

I was wondering if someone could explain the grounding electrode rule to me.
The way that I interpret the rule when you have an underground water pipe as your grounding electrode, as permitted by 250.52-A1, you shall supplement it with an an?additional grounding elctrode, 253.53-D2, with a type as specified in 250.52-A-1-7.
When you use rod or pipe for the supplement grounding it shall comply with 250.56.
Who determines the 25 ohms or less. Is it just practice that everyone installs the 2nd ground rod. I have had some inspectors tell me that the code requires 2-ground rods.
I agree only if it does not have 25 ohms or less.
So do we just automatically install 2 ground rods when ever we have a underground water pipe as a grounding electrode??

 

[ryan_618]

Re: Grounding electrode

Who determines it? You must prove less than 25 Ohms to your inspector.

Driving two rods is cheaper and easier than a test.

 

[cpro123]

Re: Grounding electrode

What if you drive 2 ground rods and have 10' or more of metal water pipe on the premises?

Chris

 

[cpro123]

Re: Grounding electrode

the reason I ask is Im an inspector, we have had several contractor just put 2 ground rods instead of incorporating the cold water pie in the grounding electrode system.

We will make them incorporate the water pipe if there's 10' feet or more in the earth on the premises.

Chris

 

[hurk27]

Re: Grounding electrode

If there is a water pipe that runs more than 10' in earth it must be used. It spell's this out in 250.50

250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system. Where none of these electrodes are available, one or more of the electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used.

Only when none of these electrodes are available (250.52 (A)(1)-(A)(6)) can you just use the rods

 

[friebel]

Re: Grounding electrode

The code does not require you to drive 2 ground rods. In our area, the AHJ wants to have 2 ground rods driven, and he does not request to have this tested to see if it meets the code section 250.56 of 25 ohms or less. So the contractor takes the easy way out, and just drives two ground rods, and he is done.
Their are a couple of ways to check the main ground rod ohms, but you need special equipment to do this. One is the three-point ground test, which I have done many times in years past. But there is a new instrument out. A clamp-on tester that will clamp around your grounding conductor and measure the ohms reading. I have never used this instrument, but I like the idea, because in the three-point ground test, you have to lift the grounding conductor from the groundrod. This can be dangerous, and their have been fatalaties in lifting a main ground.

 

[pierre]

Re: Grounding electrode

I have the tester mentioned, and it is not hard to use, but still says mostly the same thing - drive the second groundrod. Here in southern NY, the conditions are such that even with 2 groundrods, we are not getting 25 ohms.

Pierre

 

[tonyi]

Re: Grounding electrode

In one place I encountered water pipe, 3 or 4 pieces of buried RMC, and two rods. Had to connect'em ALL up.

 

[Billy D]

Re: Grounding electrode

Thank you all for the input. I also install the 2 ground rods. Most inspectors realize that it's not a rquirement unless you do not have the 25 ohms, but when an inspector tells me that it is spelled out in the code, I just want to know how he interpets it. I want to make sure that I am doing the right thing and not just doing something an inspector wants and not understanding it.
We all learn from one another.
Thanks much!!

 

[karl riley]

Re: Grounding electrode

The two rods may be a Mass requirement. Check it out.

Karl