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My current main ground is improperly connected to the water line in my house and I am planning on changing it this week. It is "connected" to (read: formerly soldered, now kind-of-sort-of laying on) a random point on the supply line in the center of my house directly under the bathroom approximately 20 feet from the point at which the main water supply comes into the house.

About 3 feet next to the service panel is what I am convinced is the old water supply when steel was the norm. Instead of running a new grounding wire ~65 feet to the current main, can I run the grounding wire to the steel pipe right next to the box? I do not know any specifics about the pipe other than it being steel but I find it hard to believe that it would have been removed when they converted to copper (my house is ~150 feet from the street).

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You would be advised to not depend on the condition of some old discontinued water pipe for grounding. That pipe may have rusted and corroded so much that a lot of it is missing or not even making a low resistance connection into the earth.

If it was me looking to correct this condition I would contact my local building / electrical safety agency and/or inspectors and determine if you can ground with a copper clad steel grounding rod that you would pound 8 or 10 feet into the ground outside the foundation near the electrical service box. Then the appropriate size heavy gauge copper wire would be run from the service panel to the ground rod.

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  • Can probably also drill a hole through slab near water line. Put long rod in hole, then run copper from panel to rod, stopping to bond with water pipe (both sides of water meter if it is there). – Edwin Jun 24 '13 at 2:45
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    @Edwin - Is it not better to put grounding rods outside where there is more hope that the earth will have some moisture added to it periodically? – Michael Karas♦ Jun 24 '13 at 4:14
  • For what it's worth after a recent replacement of my iron supply pipe I was required to drive a 8' copper rod in my basement floor. The inspector did allow me to drive it through the stone foundation as I had only 6 feet of headroom. – mikes Jun 24 '13 at 10:30
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    @mikes - Are you saying that you installed it from inside the basement but at an angle through the foundation out into the earth? I am proposing that the rod be placed outside the basement wall and route the heavy gauge copper wire out through the wall above the basement and then to the ground rod as long as this approved by local regulations and electrical code. – Michael Karas♦ Jun 24 '13 at 10:41
  • There may be local variations but as far as it being outside it maybe to keep water from leaking through the foundation. Not as much of an issue with a piled stone foundation. – mikes Jun 24 '13 at 20:11
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You may be able to use the old steel pipe, if the resistance to ground is less than 25 ohms. Mike Holt has a good article that explains how to measure ground resistance. If the resistance to ground is greater than 25 ohms, you'll need a new ground electrode or additional ground electrodes.

National Electrical Code 2011

Article 250 Grounding and Bonding

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)(4) through (A)(8). 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.

National Electrical Code also provides a list of electrodes permitted for grounding (250.52(A)(1) through (8)).

  1. Metal Underground Water Pipe.
  2. Metal Frame of the Building or Structure.
  3. Concrete-Encased Electrode.
  4. Ground Ring.
  5. Rod and Pipe Electrodes.
  6. Other Listed Electrodes.
  7. Plate Electrodes.
  8. Other Local Metal Underground Systems or Structures.

If the Authority Having Jurisdiction (AHJ) does not determine that the old pipe is adequate for grounding, you can use any of the above methods to provide additional ground electrodes.

More Reading

Fluke provides a good explanation of the Fall of potential test procedure.

Basically you disconnect the earth electrode from the system, then place two stakes in a line a specific distance from the earth electrode. A GEO Earth Ground Tester is connected to the stakes and the electrode, and then generates a known current between the outer stake and the electrode. The drop in voltage between the inner stake an the electrode is used to calculate the resistance of the earth electrode.

enter image description here

In both tests described in the Mike Holt article, expensive specialized meters are used to measure the electrode resistance. It's not likely a DIYer will be conducting this testing, so you'll have to relay on the AHJ to determine if an electrode is sufficient.

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    Is a ground resistance tester just a glorified multimeter? In other words, could I use any multimeter with an ohms setting to do the test? – Evan Jun 24 '13 at 13:01
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    @Evan Not according to the Mike Holt article, he is describing an impedance measurement using an oscillator. Not that the requirement is met once 2 rods are installed, even if the total resistance of both rods is above 25 ohms, subject to AHJ approval. – HerrBag Jun 24 '13 at 13:56
  • You could use a Fluke Earth Ground Clamp Meter, if you've got 1700 bucks laying around. – Tester101 Jun 24 '13 at 15:59
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You need to sink a ground rod into the ground untill it zeroes a megaohm meter. Usually it is best to put it near your panel. Don't believe that less than 25 ohm crap, you want that megger at zero! Then and only then will you have a solid ground. And no, you cannot use a regular multi meter it has to be a megaohm meter.

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