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Danny Mai 06-08-2011 01:45 PM

Electrical
 
I just wanted to know how to measure or get an earth resistance of an electrode, i know it should be 25ohms or less. Can i do it with a multi-meter or need a special instrument? If with a multi-meter, how to connect or place the probes?

a7ecorsair 06-08-2011 10:47 PM

Quote:

Originally Posted by Danny Mai (Post 663462)
I just wanted to know how to measure or get an earth resistance of an electrode, i know it should be 25ohms or less. Can i do it with a multi-meter or need a special instrument? If with a multi-meter, how to connect or place the probes?

Yes, you can use a multimeter but you will need a second point of contact. What are you trying to accomplish by making this measurement?

frenchelectrican 06-08-2011 11:28 PM

Quote:

Originally Posted by a7ecorsair (Post 663851)
Yes, you can use a multimeter but you will need a second point of contact. What are you trying to accomplish by making this measurement?

One thing it will come to my mind is that some peoples will try to get away with single grounding electrode but majorty of the time it will be much wiser to install second ground rod and be done with it.

And the other thing when someone do the earth testing or ground testing the soil condition will really affect the test ditto with weather pattern as well that will change a bit.

Few EC's will have specal equiment to do the ground testing to get under 25 ohms.{ this testing methold genrally are not cheap so you can see why it cheaper to just sink second ground rods and be done with it }

Merci,
Marc

Speedy Petey 06-09-2011 05:17 AM

Quote:

Originally Posted by Danny Mai (Post 663462)
I just wanted to know how to measure or get an earth resistance of an electrode, i know it should be 25ohms or less. Can i do it with a multi-meter or need a special instrument? If with a multi-meter, how to connect or place the probes?

NO, this absolutely cannot be done with a common multi-meter. The specialized meter for this test is in the $1000 and up range.

I'll also ask, WHY would you need to make this test???
Unless you are looking to get some crazy low numbers to ground an antenna systems or something like that what you are looking for is pretty much useless.

a7ecorsair 06-09-2011 08:18 AM

Frenchy and Speedy. Just so you know I'm not wacko. When I wired my house and before I connected my UFER GEC to the panel, I thought I'd see how good of connection and ground path I had back the the meter pedestal which is 80' from the panel. The POCO grounded the meter pedestal with an 8 foot rod. I measured about 60Ω from the GEC (before connecting it to the neutal bar) to the neutral bar. So, my path was the GEC to the UFER through the earth to the ground rod through the neutral back to the panel neutral bar.
Is the value precise? Maybe not but I did confirm that I had a complete path.

Danny Mai 06-10-2011 11:04 AM

I'm studying electrical through correspondence course, and what i see is that there are some electricians just write a figure on the installation form saying its below 25ohms, which i know it should be below 25. But i want to make sure it's below that figure and or if he should plant another ground rod or do something else to achieve it, that's why i want to know if i can take a measurement with a multi-meter.

brric 06-10-2011 11:10 AM

Drive another rod at least 6' from the other one, connect them together and be done with it. With multiple rods it does not matter what the meaurement is. It will cost far more to obtain a measurement than it will to drive another rod.

Danny Mai 06-10-2011 11:15 AM

thank you, but can i take reading of the 2 rods with a multimeter?

brric 06-10-2011 11:36 AM

Quote:

Originally Posted by Danny Mai (Post 664663)
thank you, but can i take reading of the 2 rods with a multimeter?

No you can't. See post #4.

Speedy Petey 06-10-2011 03:45 PM

Quote:

Originally Posted by Danny Mai (Post 664656)
I'm studying electrical through correspondence course, and what i see is that there are some electricians just write a figure on the installation form saying its below 25ohms, which i know it should be below 25.

Then you would also know that sinking a second rod eliminates the 25 ohm requirement all together. :whistling2:


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