# Establishing / verifying <25 Ohm ground



## Zog (Apr 15, 2009)

galanm said:


> From what I've been able to discern, a building ground should be 25 Ohms or less. My question is what reference is to be used to verify that when tying shielding framework or machinery to the building plane.
> 
> Where do we reference the original ground to.


You are referencing your ground rod(s)/grid to earth. The best way to do this is a 3 point FOP test.


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## galanm (May 3, 2010)

*Thanks.....Now:*

In your experience, how often is it really established at <25 Ohms?
New construction?
Existing construction?
Upgrades with out tearing the building down and re-doing the ground ring?


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## Zog (Apr 15, 2009)

galanm said:


> In your experience, how often is it really established at <25 Ohms?
> New construction?
> Existing construction?
> Upgrades with out tearing the building down and re-doing the ground ring?


For residential, almost never, likely you won't ne lees than 25 ohms and end up driving another rod anyways, so most people drive 2 rods and forget it. 

Now for industrial facilities woth more complex grouding systems that have to meet stricter requirements (<5 or 1 ohm, depending on the facility) it is always done during commisioning, sometimes re-verified for existing, and usually after upgrades.


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## galanm (May 3, 2010)

*Ground establishment records.*

Should, then, there be a record of that commissioning and related earth resistivity in house? Or would it stay with the original GC? I'm doing work in a medical devices manufacturing plant heavily regulated by the FDA. Are there regulations specific to this venue?


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## Zog (Apr 15, 2009)

galanm said:


> Should, then, there be a record of that commissioning and related earth resistivity in house? Or would it stay with the original GC? I'm doing work in a medical devices manufacturing plant heavily regulated by the FDA. Are there regulations specific to this venue?


Most industrial facilities require <5 ohms, but the design can call for less if they want and often they do for medical facilities. There should be a record of the test in house.


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## galanm (May 3, 2010)

*Thanks*

I will investigate their documentation further.:thumbup:


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## Zog (Apr 15, 2009)

galanm said:


> I will investigate their documentation further.:thumbup:


I recently moved from MI and worked for a couple companies up there that do ground testing so if you need a test done I can refer you to someone local.


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