Amp reading on ground

ryderimmel

Member
Location
vancouver wa
Occupation
Journeyman
I have a wireless tower site with an extensive grounding. I am picking up .2-.4 AC amps on the ground. I shut the whole site down and the electrode wire still had the .4 amp reading at the meter enclosure. We have determined that the reading is coming from the ground ring around the exterior of the shelter and tower. The chain link fence has every post with a welded ground attached to the ground system. We are picking up the reading on the 2 posts closest to the meter. Other posts closer to the tower had 0 amp reading. Is this caused by some kind of induction from other underground utilities? Is it possible that its from the antennas on the tower that are still powered by batteries when the AC power is shut off? I did notice that the amp reading on the ground drops when the rectifiers are shut off. I wanted to blame the rectifiers but I still had the .4 amp reading on the electrode wire when the site AC was shut off. Keep in mind that this site in on a hill top with approximately 50 ground rods and anything metal on the site has a welded or mechanical connection attached to the ground ring or system.
 

bwat

EE
Location
Western PA
Occupation
EE
It’s my understanding that it’s pretty common to have a volt or two to ground from utility neutral. With 1 volt and a residential GES with 25 ohms, it’s below 0.05A. But since you have a large number of ground rods and other electrodes, even a small amount of voltage (less than 1v) on the neutral seems reasonable to produce what you’re measuring.
 

bwat

EE
Location
Western PA
Occupation
EE
Why would current flow through the earth when you have provided such a better path
And I don’t have any numbers to provide, but something I’ve heard said many times is that the earth is actually a really great conductor. It’s just difficult to connect to it (like a contact resistance). So when you have an extensive GES, you really reduced that “contact resistance” to the conductor (earth) and can then utilize its conductive properties. So it can actually be a great path.

I’ve had similar conversations recently about this same topic. I need to look up some actual numbers to support such statements..
 

LarryFine

Master Electrician Electric Contractor Richmond VA
If there are no other power sources nearby, then the current must be from a voltage difference between the incoming utility's grounded conductor and the earth.

I read through the OP again. If you're reading AC, the batteries may be powering inverters
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
It may not be, but it is good enough to have concentrated .5 amp onto that wire and that is the path he is concerned with.
You misunderstood my post. He was saying the wire was a great path. Sometimes the wire isn’t all that good a path. Not cleaning the terminations correctly will create a less than ideal path...
I was saying the wire may not be that great a path and the earth is carrying current.
 
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bwat

EE
Location
Western PA
Occupation
EE
I would assume the distribution system is an MGN and it is POCO neutral current heading home that you are measuring. We did two cell towers 15 years ago and IIRC the resistance spec on the GES was 4 ohms. IT is very conceivable that some of those lazy opportunistic electrons are using MY GES.
 

ryderimmel

Member
Location
vancouver wa
Occupation
Journeyman
Thanks all for the responses. I will submit a report today of my findings and the comments really help with additional info and possibilities. Since there was no measurable voltage I can deduce that there are no issues with damage to equipment and shock hazards to personnel.
 
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