Grounding 2 point test result failed

[synchro]

And everything is energized

From transformer N-G GEC to main panel. From main panel to main busbar, from main bus bar to the ground rod.

Because you are making measurements with the system energized, I suggest that you put a clamp meter around the various conductors for grounding that you've mentioned. It's possible that there is current passing through one or more of those conductors... for example, because of more than one bonding point made to the neutral. Such currents could produce small voltage drops across the conductors and that may interfere with resistance measurements and produce incorrect results.

 

[PowerdT]

Divide and conquer. What is the resistance from the rod to the panel ground bus? What is the resistance from the panel ground bus to the grounding bar? Can you see a wire on that ground bar going somewhere? Is it going to the panel ground bus, building steel, something else? Is there a system bonding jumper at the transformer or first disconnect?

What is the resistance from the rod to the panel ground bus? Not measured but what ohms do you expect?

What is the resistance from the panel ground bus to the grounding bar?Not measured but what ohms do you expect?

Can you see a wire on that ground bar going somewhere? Yes, 2 wires on ground bar. One is from the transformer and the 2nd wire to structural steel.

Is it going to the panel ground bus, building steel, something else? Panel was not opened but I see no wires coming out from the panel unless the GEC is with the feeder in raceway.

Is there a system bonding jumper at the transformer or first disconnect? I dnt think so

 

[PowerdT]

By the way, i dnt think it matters but I’m the test was 3 point fall method

 

[don_resqcapt19]

A

Another test we did in same building

Transformer N-G —>rod —>busbar.

The rod measures 1ohms. Then, When we measure the resistance between rod and busbar result is around 10ohms.

Then the rod and the busbar are not physically connected. Again an isolated grounding system was a very common requirement for electronic equipment for many years, even though it was always a code violation.

There was a manufacturing plant that I worked at that had Distributed Control System for process control. The instrument grounding was connected to a completely isolated grounding electrode using insulated conductors per the installation requirements of the DCS manufacturer. On startup, their techs verified this isolation of the instrument grounding system from the electrical grounding system.
Where there were nearby thunderstorms in the first summer of operation, they would experience failures of some of the control boards. They asked us to prove that the grounding system was truly isolated which we did, but at the same time we told that that the isolation that the DCS manufacturer requires is the actual cause of the board failures. The third summer they permitted us to make a single point bonding connection, as required by the NEC, between the DCS grounding electrode system and the electrical grounding electrode system and the problem went away.

Now the documentation from the DCS manufacturer requires the single point bonding between the instrument grounding system and the electrical grounding system.

 

[Joethemechanic]

Just for laughs, AmpClamp your grounding conductors. See if there is any current flowing through them.

 

[PowerdT]

Then the rod and the busbar are not physically connected. Again an isolated grounding system was a very common requirement for electronic equipment for many years, even though it was always a code violation.

There was a manufacturing plant that I worked at that had Distributed Control System for process control. The instrument grounding was connected to a completely isolated grounding electrode using insulated conductors per the installation requirements of the DCS manufacturer. On startup, their techs verified this isolation of the instrument grounding system from the electrical grounding system.
Where there were nearby thunderstorms in the first summer of operation, they would experience failures of some of the control boards. They asked us to prove that the grounding system was truly isolated which we did, but at the same time we told that that the isolation that the DCS manufacturer requires is the actual cause of the board failures. The third summer they permitted us to make a single point bonding connection, as required by the NEC, between the DCS grounding electrode system and the electrical grounding electrode system and the problem went away.

Now the documentation from the DCS manufacturer requires the single point bonding between the instrument grounding system and the electrical grounding system.

That’s interesting. Not only that it is code violation, even if we install new rod near server busbar, still is not going to solve the problem.

I think it’s better to route gec from main busbar to server busbar and connect all other busbar and rod including structure steel

 

[PowerdT]

Just for laughs, AmpClamp your grounding conductors. See if there is any current flowing through them.

Haha. Will do.

How big difference it makes when you do this resistance test when it is energized?

 

[don_resqcapt19]

That’s interesting. Not only that it is code violation, even if we install new rod near server busbar, still is not going to solve the problem.

I think it’s better to route gec from main busbar to server busbar and connect all other busbar and rod including structure steel

Correct, you need a bond between the two. An additional ground rod without a connection to the electrical grounding system will not change anything.
Yes it is a code violation, but up through the 90s, that was the instructions from some manufacturers of "sensitive electronic equipment. I understand that even today you can find some CNC machines that still have an instruction to provide a totally isolated grounding system for the equipment.

 

[jim dungar]

Correct, you need a bond between the two. An additional ground rod without a connection to the electrical grounding system will not change anything.
Yes it is a code violation, but up through the 90s, that was the instructions from some manufacturers of "sensitive electronic equipment. I understand that even today you can find some CNC machines that still have an instruction to provide a totally isolated grounding system for the equipment.

Yep, and has been mention, it does not help with anything. Well maybe a correct installation gives the manufacturer a way to avoid warranty by claiming you didn't follow their instructions.

 

[suemarkp]

What is the resistance from the rod to the panel ground bus? Not measured but what ohms do you expect? Less than an ohm.

What is the resistance from the panel ground bus to the grounding bar?Not measured but what ohms do you expect? Less than an ohm.

Can you see a wire on that ground bar going somewhere? Yes, 2 wires on ground bar. One is from the transformer and the 2nd wire to structural steel. Where is it going on the transformer -- to the neutral or to the can?

Is it going to the panel ground bus, building steel, something else? Panel was not opened but I see no wires coming out from the panel unless the GEC is with the feeder in raceway.

Is there a system bonding jumper at the transformer or first disconnect? I dnt think so. This may be the problem.

The transformer needs it neutral bonded to the equipment somewhere (system bonding jumper). Maybe it was done in the panel instead of at the transformer. If it is not bonded, that neutral is isolated from the can. Grounding the can serves one purpose. Bonding the equipment ground to the neutral serves another purpose. Without a system bonding jumper, these two are separated. The ground bar should really be thought of as bonding and not earthing. These should be wired connections so all you need is a simple ohm meter and not a fancy fall of potential tester. Resistance would be less than 1 ohm unless these conductors are 1000' long.

 

[PowerdT]

I was not able to open transformer to verify, if necessary I will schedule it. However, I was told usually they bond N-G inside transformer so I assume the system bonding jumper might be inside transformer bonded to enclosure.

I open the service entrance panel board, which doesn’t show N-G bond,
I see 1/0 GEC coming from transformer and terminated to ground busbar inside the panel board.

Then from panel board 2AWG Ground wire leaves the panel board and terminates to the main busbar outside.

From the main busbar 2AWG terminated to ground rod.

 

[suemarkp]

So this sounds you have wired connections between transformer, panelboard, and ground bar. Unless there is a bad connection somewhere, how could these not have a resistance of well under 1 ohm. You got a good battery in your meter?? I'd also make sure the system is off, as any current on those wires could fool the ohm meter (I read negative ohms once on a system, and it was because there was DC current flowing on it).

 

[Joethemechanic]

as any current on those wires could fool the ohm meter

That is why I suggested amp clamping the grounding conductor

 

[PowerdT]

So this sounds you have wired connections between transformer, panelboard, and ground bar. Unless there is a bad connection somewhere, how could these not have a resistance of well under 1 ohm. You got a good battery in your meter?? I'd also make sure the system is off, as any current on those wires could fool the ohm meter (I read negative ohms once on a system, and it was because there was DC current flowing on it).

Yea I am not sure why the resistance is higher. I was not present when the test was done so I am planning to be present and retest the system again. I am gonna make sure battery is good.

How big difference does it make with the system on? It’s going to be hard to coordinate to have the power off.

That is why I suggested amp clamping the grounding conductor
Also I will amp clamp on the ground wire.

 

[Joethemechanic]

I was not present when the test was done

Oh Boy are you going to learn never to trust any kind of measurements from the Oompa-Loompas

 

[PowerdT]

Oh Boy are you going to learn never to trust any kind of measurements from the Oompa-Loompas

Haha, i hope it doesn’t change my mind about oompa-Loompas.

I will try to upload the single line diagram and show you guys what they test

 

[Joethemechanic]

I can't tell you how many times I've gotten a late night phone call because something is down, and when I ask voltage, amperage, resistance, pressure, temperature or whatever and I get nothing but wild numbers that don't make sense. Now I get dressed and go out there, When I get there I find out they were measuring wrong, or they were too lazy to do the tests so they just made up numbers in their head

 

[PowerdT]

I can't tell you how many times I've gotten a late night phone call because something is down, and when I ask voltage, amperage, resistance, pressure, temperature or whatever and I get nothing but wild numbers that don't make sense. Now I get dressed and go out there, When I get there I find out they were measuring wrong, or they were too lazy to do the tests so they just made up numbers in their head

That’s hilarious. I guess we will find out if my situation are similar

 

[synchro]

If you measure a significant current through a ground conductor with a clamp meter, then that may interfere with a resistance measurement made across the conductor. But if this happens, I suggest measuring the voltage across the conductor and then dividing it by the current measured by the clamp meter to get the resistance via Omm's law. Use the most sensitive setting on the meter. A true RMS clamp meter would be desireable because there could be harmonics present.

 

[Joethemechanic]

There is always going to be a small current on the grounding conductor that runs between the NG bond and the ground rod. After that you really shouldn't have any.