Light pole

[Dsg319]

At an old compressor station and replaced light poles with new and old poles were tied in to the existing ground grid, but new ones are set in place on concrete piers and old wire won’t reach. I have new circuit wire and egc bonded to pole. And was curious and got my ohm meter and checked from light pole to remote earth (piece of metal drove in earth). And got 0ohms. Is this method a good way(or at least work in a pinch) to check for resistance from pole to earth for touch potential, and lighting protection?

 

[Hv&Lv]

I would have thought you would have got OL

 

[Dsg319]

Here’s some pics

 

[winnie]

I would find a reading of 0 Ohms suspicious.

Your reference electrode is a simple rod in earth which should have significant resistance. Even if the grounding grid at the compressor station were perfect; you would still measure the resistance of the reference electrode.

Jon

 

[zbang]

(opinions seem to differ on this)
Is the rebar bonded to the EGC? If it is, that's about the best you're going to do for both lightning protection and touch potential (the second would be a ground rod at the pole, also bonded to the EGC). If not, a good EGC is the best you can do.

Measuring DC continuity tells you that there is a metallic path, but not much else. Actual ground resistance measurement needs a special meter and techniques.

 

[synchro]

Try exchanging the red and black test leads so that red is on the metal stuck in the earth and black is on the pole, and then measure again.
Even on the lowest scale of the "ohms" mode the meter applies a relatively low amount of DC current and then measures the resulting voltage developed by that current across the resistance being measured. On my Fluke 111 the current on the lowest ohms scale is about 1.5 mA. Across a 10 ohm resistor that current would develop 1.5 mA x 10 ohms = 15 millivolts. When you stick a metal object in the earth you may be developing a small DC voltage because of electrochemical effects (like a battery) that could be tens or hundreds of millivolts, and that may be causing the ohms measurement to be inaccurate. This DC voltage will have a certain polarity and that's why I mentioned flipping the test leads around to see if there is any difference.

Like zbang said you need to use a specialized meter to accurately measure the ground resistance. These meters apply AC currents and so the electrochemical effects I mentioned do not interfere with the measurement.

 

[Dsg319]

I switched leads and it changed it as you had said. Got ol from pole to earth and still between the old old grounding electrode to the pole which would reach which is probably tied together with same rebar and bolts. There was around 4.0 ohms

 

[Dsg319]

I know I ask a lot of questions on here, BUT can’t learn if you don’t ask.

 

[infinity]

The pole requires connection to the EGC as you have done.

I know I ask a lot of questions on here, BUT can’t learn if you don’t ask.

Please keep asking, that's why we're all here.

 

[Dsg319]

Really thinking back should have known better, because we perform ground fall potential test on stations with ground electrodes out the wazoo and still don’t get zero ohms lol