How to test ground rod resistance

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  #1  
Old 08-26-05, 09:14 PM
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How to test ground rod resistance

Can anyone tell me how to test the resistance of a new ground rod I just installed? Can I simply use the Ohms setting on a multimeter, or is there special equipment that has to be used?

Also, when running the ground wire to this rod, should it be in conduit or can it be the bare wire. If bare, is there a special clamp to use where it exits the panel?

Thanks for any help any of you might have.
 
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Old 08-26-05, 09:29 PM
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Here is a link that specifies how the testing is done.

http://www.msha.gov/S&HINFO/TECHRPT/GROUND/GROUNDRE.HTM

If you are asking in regards to the 25 ohm resistance on a ground rod it is easier to just drive a second rod.

The equipment is expensive. Here is an example of the tester.

http://www.jensentools.com/product/g...arent_id=10110

Normally only #6 or smaller needs to be protected, but could vary based on local rules. NEC does not require the wire going to the rod to be larger than #6.
 
  #3  
Old 08-27-05, 07:07 AM
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It is not actually possible to do this with a standard multi-meter and get any kind of a reading you can use. The local AHJ will not agree to anything unless you can show them your readings and even then they can choose to adopt the theory of (2) ground rods are better concept which is what they have done in our area.

Here is the manufacturer of the equipment that can do the resistance ohms test and the model 382152 sells for about $ 199.00 dollars.
http://www.extech.com/instrument/cat...oundResis.html

The 382152 is the less expensive and since it uses actual leads to ground will most likely get the attention of the inspector before a clamp on will if that is your goal. ( and for those electricians who still fight the (2) ground rod issue )

Regardless it is cheaper to simply buy another ground rod ( 6-10 bucks ) additional # 6 AWG Bare wire ( does not need to be protected unless subject to physical damage ) and their should be a small hole made into the panel itself for the wire to exit and no connector is needed in using this build in whole. ( P.S. you will still need to knock out this small hole )

My suggestion is to simply spend about $ 20.00 and add a second rod and you wont need to worry. Also again your local AHJ may demand it anyway.
 

Last edited by ElectricalMan; 08-27-05 at 01:16 PM. Reason: Winnie brings up a GREAT point...Booyah Winnie !
  #4  
Old 08-28-05, 07:38 PM
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Thanks guys. I'll just go the cheaper route and drive another ground rod.
 

Last edited by milhouse; 08-29-05 at 03:46 AM.
  #5  
Old 08-29-05, 03:48 AM
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ElectricalMan, I did notice the small knockout you mentioned. It's about 1/4". Is this this what you're talking about? Do I just pass the ground wire through this hole without securing it like you would NM with a cable clamp?

Also, when running the ground wire outside, do I just drill through the cinder block wall, pass the wire through and then seal it with silicone, or do I have to pass it through conduit in the the wall?

Thanks for everyone's help. Just trying to get every detail before I do my work.
 
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Old 08-29-05, 05:44 AM
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Yes, that little 1/4" hole in the bottom of the panel usually near the center is for the GEC and it should pass through it and you do not need a connector for it...plus their is no connector that would possibly fit that hole size anyway.

Once you are through suport it as normal and within 12" from when it leaves the bottom of the panel.....and you really do not need to pipe through the wall, just run the # 6 CU through the hole...just drill it through and run it out and down to your ground rod and you are fine.
 
  #7  
Old 08-29-05, 11:32 AM
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Quick note: If, for any reason, you do need to use conduit for mechanical protection (say if you are coming down the side of a wall subject to damage from mowing,) then either use plastic conduit, or be sure to bond the ground wire to the conduit at _both_ ends.
 
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Old 09-01-05, 12:05 PM
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Thanks ElectricalMan and Winnie.

One more quick simple, question about grounding if you don't mind. Where I'm going to drive my 2nd ground rod, the ground wire will pass maybe within 6 inches or so of the gas line. Will this be a problem? It won't be in direct contact or bonded to the line, but I want to make sure before I do it. If it is a problem, would 1/2" pvc correct it?

This forum has excellent advice. There's only so much you can get from the DIY books.

Thanks again.
 
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