General Technical & Safety Information

[Tim]

Originally Posted by OTAFAN

Can an antenna ground stake be checked for resistance with a multimeter, or would one have to use the expensive test equipment with multiple leads as seen on various websites discussing ground testing?

And if one could use their multimeter, where would the leads be placed for resistance reading?

Thanks in advance for any kind help!

To check for resistance between the ground rod and the earth? Not with a multimeter that I am aware of.

Do you have unusual soil conditions that you wary of your ground connection?

[OTAFAN]

Do you have unusual soil conditions that you wary of your ground connection?

No, I think my soil here is a combination of clay and sand in south OC, CA. Probably better than many other locations, I'm guessing.

I was just wondering how one could check their ground stake for resistance, rather than just rely on typical measurements you see posted on the web. For instance, for a separate antenna mast ground rod bonding back to your service entrance, the NEC wants 25 Ohms or less. How would you know your ground stake complies with the code unless you want to fork over some bucks for sophisticated equipment I've read about or hire an electrician at Union wages?

I didn't think it would be as easy as using a multimeter, but I guess I was hoping against hope.

Thanks, Tim for your reply. Anything else is appreciated too.

[GroundUrMast]

The traditional method of measuring ground rod resistance has been the "Three Point Fall of Potential" (TPFP) though there are alternate methods as well. The cost of specialized equipment with recognized certifications is likely well beyond the budget of most DIY'ers. Here is a somewhat technical description that make reference to The Institute of Electrical and Electronics Engineers in IEEE Standard #81, IEEE Recommended Guide for Measuring Ground Resistance and Potential Gradients in the Earth.

The TPFP provides a means of accounting or the variability of soil conductivity in the area near the ground rod under test, and also account for the resistance in the test connections. This method also avoids the hazards of breaking the connection of a live system from the ground rod... If there were fault current flowing in the grounding system, hazardous voltage could be present when the ground conductor is taken loose from the ground rod. (I've added a safety warning to my post #24 of this thread.)

Having rambled enough... If you simply drive a rod into the earth and then connect a multi-meter between the new rod and the existing electrical service ground, check for AC and DC voltage differences before checking resistance. You may find there is enough current through the earth due to any number of possible sources. Only if there is negligible voltage present can you then take a DC ohm reading that would provide an approximation of the new ground rod resistance. Though not likely, you can encounter hazardous voltage differences between different points on the ground, so don't allow yourself to touch both points at the same time.

[OTAFAN]

Though not likely, you can encounter hazardous voltage differences between different points on the ground, so don't allow yourself to touch both points at the same time.

Do you mean testing or touching the 6 AWG bonding wire and separate antenna ground stake at the same time?

This ground stuff is not for the faint of heart it seems. But "Safety First" is paramount with electricity et al, for sure.

Thanks for your input once again!

[GroundUrMast]

Originally Posted by OTAFAN

No, I think my soil here is a combination of clay and sand in south OC, CA. Probably better than many other locations, I'm guessing.

I was just wondering how one could check their ground stake for resistance, rather than just rely on typical measurements you see posted on the web. For instance, for a separate antenna mast ground rod bonding back to your service entrance, the NEC wants 25 Ohms or less. How would you know your ground stake complies with the code unless you want to fork over some bucks for sophisticated equipment I've read about or hire an electrician at Union wages?

I didn't think it would be as easy as using a multimeter, but I guess I was hoping against hope.

Thanks, Tim for your reply. Anything else is appreciated too.

You are correct, the NEC makes reference to 25 ohms in 250.53 and requires an additional rod if that value is not achieved. Until a few years ago, the area I live in was so well known for poor ground conductivity that the inspectors and electricians all assumed that two rods were required. Now this area requires all new construction to use a Ufer ground connection that makes use of the steel rebar in the foundation.

But remember that your electrical service ground is only one of hundreds or even thousands of connections to earth that are all interconnected trough the power utility neutral. For static discharge purposes only, a high resistance connection of several thousand ohms is adequate to bleed off the charge. Your existing electrical service ground is going to do just fine unless it was installed incorrectly or has been damaged.

Focus on bonding your mast and coax to the existing electrical service grounding system and sleep well.

[GroundUrMast]

Originally Posted by OTAFAN

Do you mean testing or touching the 6 AWG bonding wire and separate antenna ground stake at the same time?

This ground stuff is not for the faint of heart it seems. But "Safety First" is paramount with electricity et al, for sure.

Thanks for your input once again!

Yes. For example I live in an area that has high voltage transmission lines within a quarter mile. If there was a line down there will be high voltage at the point of contact to the earth and the voltage will drop lower and lower the further you move away from the downed line. It's entirely possible for hazardous voltage to develop across the property near such a fault. The power line that feeds my street is at least a 7200 volt line. A fault at the front of my lot would create a dangerous voltage gradient across some part of my lot.

The further the new rod is from you electrical service the greater the possibility of encountering some voltage difference. Simply avoid putting your body between the two "grounds" if they are not bonded properly.

[OTAFAN]

Focus on bonding your mast and coax to the existing electrical service grounding system and sleep well.

Thanks for your patience in answering my questions, GroundUrMast.

I think it's much overlooked and not understood by the majority of DIY'ers and the general public at large. Most of us just put up an antenna with no thought that now it's in the electrical circuit of our homes. And no doubt, most have had no issues, fortunately, but still there are fatalities or injuries each year I'm sure from ignorance of grounding and safety issues.

I think if we OTA people will follow the NEC and our State Electrical Codes, along with our local head electricians' advice (if consulted) who is the final authority as I understand, we should be able to sleep well at nights.

This has all become fascinating stuff for me and I'm all ears with whatever you continue to post in this thread. One of the reasons I joined TV Fool was to learn. When I was in school many, many years ago now, my teachers always said there are never any foolish questions, only ones that are not asked which prolong ignorance. I think they were referring to, Dr. Charles Steinmetz, the engineering genius, who said, "there are no foolish questions, and no man becomes a fool until he has stopped asking questions."

Thanks a million, GroundUrMast!

[Tim]

Originally Posted by GroundUrMast

Focus on bonding your mast and coax to the existing electrical service grounding system and sleep well.

Good advice. If your added ground rod, mast, coax, etc are all properly bonded back to the electrical service ground, then everything will be at the same electrical potential and all is well.

[OTAFAN]

Originally Posted by GroundUrMast

But remember that your electrical service ground is only one of hundreds or even thousands of connections to earth that are all interconnected trough the power utility neutral.

Do you mean all the electrical wiring in one's home or all the way upstream to the local power company; or both?

Thanks as always.....

[GroundUrMast]

Originally Posted by OTAFAN

Do you mean all the electrical wiring in one's home or all the way upstream to the local power company; or both?

Thanks as always.....

Both...

In a typical residential area with above ground poles, you see one or more high voltage lines at the top of the pole. If you look closely, the pole mounted transformer is connected to one of the top lines. Of course, those high voltage line(s) are not directly connected to earth, but the line just below the transformer (the power company neutral) is connected to earth, in some cases at every pole by way of a wire that runs from the neutral down the pole and into the soil. The drop wire that runs from the transformer to your home typically is a set of three wires, one of which is not insulated... This uninsulated wire is connected to the power company neutral (which is tied to earth at multiple locations in their system) and then at your electrical service panel, a connection from the neutral to earth is made via a ground rod, rebar, water pipe, well casing, etc.

So, the neutral lines in your home are connected to the neutral lines in your neighbors homes through the power company neutral. Even if your ground rod (or other grounding option) has high resistance to earth, the many connections to earth made by the power company and your neighbors ensures that the total resistance between the neutral/ground bus in your service panel will be very low and reliable.

All that these connections to earth are intended for is the prevention of static charge buildup between the power grid and earth. The high voltage lines are also protected from static buildup because the power transformer windings have very little DC resistance. Once the neutral terminal of the transformer is connected to a grounded neutral you would be able to measure the DC continuity to ground when you test each of the 'non-grounded' terminals of the transformer.

I know I'm repeating myself, but very few antenna installations actually need a ground rod to be added... Simply bonding to the existing electrical service ground will provide all the ground connection that is needed and also provide protection from shock hazards.