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#101596 01/28/02 12:46 PM
Joined: Jan 2002
Posts: 3
Q
Junior Member
I work for an electrical contracting firm in Nassau Bahamas. Presently we are in dispute with an egineering firm of the method of testing required for the grounding system for a well field project. The wells a distributed over a large area. The engineers are saying to use the fall of potential method. This will be highly impracticle due to the distances involved. We only need to achieve 5 ohms or less. Is this realy necessary?

#101597 01/28/02 02:34 PM
Joined: May 2001
Posts: 717
G
Member
qknowles,
The Fall of Potential method has been around a long time, and is the time honored method of testing. You can never assume 5 ohms or under no matter the type of grounding you use.

Which testing method have you proposed different than the FOP?

#101598 01/28/02 06:10 PM
Joined: Nov 2000
Posts: 2,236
Likes: 1
Member
Ok... Fall of Potential... That's a new one for me...

Voltage Drop?

'splain, please?

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#101599 01/28/02 06:45 PM
Joined: Jan 2002
Posts: 3
Q
Junior Member
Thanks George Corron for you reply. I have done the fall of potential method before but for substations and power plants. But is it really necessay for a well field installation where we have approximately 16 interconnected ground rods each reading 2-5 ohms. Also as the well field is large to carry out a true fall of potential test would require the current injection probe be placed 14 miles away. This is not possible.

#101600 01/28/02 10:54 PM
Joined: Nov 2000
Posts: 2,236
Likes: 1
Member
Wow... 14 miles...

What the heck is the Fall of Potential Method?

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#101601 01/29/02 10:58 AM
Joined: May 2001
Posts: 717
G
Member
Sparky,
Sorry, school last night, got in late. The Fall of Potential method is probably one of the simplest tests you can perform. It simply takes the electrode being tested, (let's call it X) adds two electrodes (electrode Y at app. 62' and Z at app. 100') and measures voltage between X and Y, and amperage between X and Z.

The problem Qknowles has is that his "electrode" is MILES long, and to calculate 62% and 100%, it stretches the entire process way out. I would think (big stretch here since I don't have plans or specs for his project) that they could measure FoP individually for each well head, add resistance for conductor, and calculate the difference, but again without a lot more info on his project, that is a BIG shot in the dark.

I hate to gig you on this, but Chap. 6 of the current edition of Soares, it's also in the American Electricians handbook.

I don't have any way of inserting drawings in here, I'll try to scan one in from Soares, it may make it easier to 'see', and send it to you via e-mail.

He also likely has to come up to NICET standards, and even though the test does not change much, it may be quite rigorous. I cannot imagine quite so extensive a test in what I'm guessing is sandy soil, but again, I'm not there. Could be since I possess a broken leg though [Linked Image] . Nice little working vacation, but he'll have to push me around in a wheelbarrow [Linked Image]

#101602 01/29/02 09:41 PM
Joined: Nov 2000
Posts: 2,236
Likes: 1
Member
Yes, I need to buy those books...

So much to buy... So little money...

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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