Residential Ground Conductor Experiment

[Clayton79]

This may or may not be relevant, I had a case of arcing in a home between gas and water lines...
looked and there was no jumper around water meter..installed one. Arcing went away, obviously the current in the water lines was seeking a return path, which led me to the panel.
Visual inspection didnt reveal any severe problems until we plugged in a sawzall...then Saw a spark behind the main neutral lug. Rotted away from moisture,
Everything was returning basically on the water electrode bond...replaced panel.
You never know what’s truly bonded or connected in older homes, what has a good grounded current carrying conductor.
Cheers.


Sent from my iPhone using Tapatalk

 

[kwired]

Correct on the neutral. Now I got 22A, 13 and 9 on L1, L2 and N.

You sure you have 120/240 and not two the same phase and a neutral?

13+9= 22 and is exactly what you should have if it is two of same phase and a common neutral.

 

[mopowr steve]

[QUOTE="WasGSOHM, post: 2632261,
By the way, I have not been able to find the fatality rate before and after GFCIs were introduced back in the 70s. For some reason, who knows what?, there may be no statistically significant difference, despite the good intentions of C. Dalziel.
Must be I used the wrong combination of search terms!
[/QUOTE]
I do remember reading somewhere that GFCI reduced reported deaths by 50% during a certain time frame. Can’t remember where I read it though.

 

[kwired]

[QUOTE="WasGSOHM, post: 2632261,
By the way, I have not been able to find the fatality rate before and after GFCIs were introduced back in the 70s. For some reason, who knows what?, there may be no statistically significant difference, despite the good intentions of C. Dalziel.
Must be I used the wrong combination of search terms!

I do remember reading somewhere that GFCI reduced reported deaths by 50% during a certain time frame. Can’t remember where I read it though.
[/QUOTE]
When GFCI's first introduced to code they were only for swimming pool equipment and bathrooms mostly. So if anything you would need to see how many fatalities due to electrocution in those areas were effected at that time as they weren't typically being used much of anywhere else.

Six feet from kitchen sinks, like we had in mid 80's I don't think was too bad of an idea, I didn't and still don't feel we needed to expand to all kitchen counter top receptacles, nor did we need to include dishwashers or laundry receptacles (other than possibly if within six feet of a sink).

Outdoors and in garages and similar areas I am fine with, most the time moisture in cords and equipment trips and protects people before they ever get an opportunity to be shocked.

 

[WasGSOHM]

201221-1123 EST

WasGSOHM:

I believe your question in this thread is essentially the same as your question in Troubleshooting.

You list yourself as an EE. On this basis I believe you should have a better understanding of electrical circuit theory than what it appears you have.

Your question seems to be about the direction of power or energy flow in a circuit. You have provided insufficient information to determine this. Two resistors in series in the circuit will give you no more information than what you have with one resistor.

Do some basic thinking about how you could possibly determine whatever it is that you want to determine. Write down a clear definition of how you might do whatever it is that you want to measure.

.

Actually I have an MSEE, but I'm old. Early onset Alzeimer's?
Speaking of age, if you want to do some math, the mortality tables give me 12 more years to live, but the IRS table has me living to 102.

Some questions I ask are to get the opinion of electricians.

I disgree with the two resistor statement; if you pass current through Romex and measure the voltage drop along one line, you can tell which outlet is upstream of which other (like for determining where to place a GFCI.

With the ground current, I'm making up some fixtures to conveniently check this out, but it being Xmas other stuff keeps getting bumped ahead in the line.

 

[WasGSOHM]

Thanks guys, for the GFCI info. . .I gotta digest this.

Finally made up a 30' test lead and measured a steady 1.83 mV across the 1/8" thick ground lead, so there is some current through this wire.

Using the ground wire as a shunt, if this wire has 0.5 milliohm per foot (?), with 20' I get 1.83 mV/10 mohms = 0.2 A, quite different from the 7 mA expected capacitive current.
The worms are getting out.

If I open the connection, the other ground will be at the outside utility pole, so now I need the guts to open the connection and repeat the measurement.

 

[WasGSOHM]

The answer was in front of me the whole time.

Set my 100 ohm rheostat to zero.
Bridge the pipe/wire connection with said rheostat.
Monitor the 'stat voltage.
Open the pipe/wire connection.
Slowly crank up the resistance.
If the 'stat voltage approaches a kilovolt, leave the area immediately!

Also, I suspect the 0.2 A varies quite a bit so I need to make more measurements. Where is a strip chart recorder when you really need one??

 

[al hildenbrand]

. . . . the other ground will be at the outside utility pole, . . . .

(And from your opening post). . . . There is another conductor to earth ground at the power pole 30' away.

The equivalent circuit so far is a ground current source (not a voltage source) through a ground resistance through the service neutral to the panel ground bus out the 1/8" diameter wire to the water pipe and back into the ground.

The other loop that touches the panel ground bus is the capacitively coupled current from all the hot wires to all the ground wires.

I'm curious where you are starting from, to derive your equivalent circuit.

I well remember my surprise at learning that the Power Company transmission line lightning protection conductor, with its connection to Earth every couple of spans, was also used as the transmission circuit grounded conductor in wye distribution topologies, AND was bonded to the Earth connection at my local transformer (the transformer pole ground rod, butt plate, or ground ball, etc.) In delta transmission line topologies, there was still a lightning protection transmission line conductor with multipoint Earthing, in most cases, that was bonded to my local transformer pole's Earth connection.

So, as you collect data on the current flowing in your Grounding Electrode Conductor (GEC) at the connection to the metallic water pipe system, keep in mind how long this wire-type conductor is. Arguably it goes all the way to the actual Power Company generators, passed along through the substations.

Posters, above, have rightly also mentioned "the neighbors" as current sources. Keep in mind that your home's metallic water pipe supply, if a municipal system, or like, will have a good low impedance electrical path, through the distribution water piping, to the Grounding Electrode Conductors (GECs) of those neighbors who share the output of your local Power Company transformer secondary. All those paths are in parallel to your GEC.

 

[WasGSOHM]

I'm curious where you are starting from, to derive your equivalent circuit.

I well remember my surprise at learning that the Power Company transmission line lightning protection conductor, with its connection to Earth every couple of spans, was also used as the transmission circuit grounded conductor in wye distribution topologies, AND was bonded to the Earth connection at my local transformer (the transformer pole ground rod, butt plate, or ground ball, etc.) In delta transmission line topologies, there was still a lightning protection transmission line conductor with multipoint Earthing, in most cases, that was bonded to my local transformer pole's Earth connection.

So, as you collect data on the current flowing in your Grounding Electrode Conductor (GEC) at the connection to the metallic water pipe system, keep in mind how long this wire-type conductor is. Arguably it goes all the way to the actual Power Company generators, passed along through the substations.

Posters, above, have rightly also mentioned "the neighbors" as current sources. Keep in mind that your home's metallic water pipe supply, if a municipal system, or like, will have a good low impedance electrical path, through the distribution water piping, to the Grounding Electrode Conductors (GECs) of those neighbors who share the output of your local Power Company transformer secondary. All those paths are in parallel to your GEC.

Yeah, I'm going to take small bites out of this puzzle. Take two bites, spit one out.

Added bonus, I found out where we are getting the water hammer noise. Cut 2x4, add copper clamp, do not fall off ladder.

And I need to take two readings.
One time I measured the source resistance of a current leak from a fridge shell to ground.
The R value came out negative which I think means the R value depended on the I through it, not like a fixed value of resistance.

An incandescent bulb shows this effect.

Speaking of equivalent circuits, a regular outlet can be modeled as 120vac in series with a half ohm resistance (depending on the length of Romex back to the panel).

 

[ptonsparky]

Curious. You're wearing your PPE, right?

 

[WasGSOHM]

Curious. You're wearing your PPE, right?

That was the plan when I took the panel cover off. Level 1 gear.

But in the cold light of day and in the heat of battle, etc., etc., . . .well. . .if I poke around I make baffles out of cardboard to prevent my metal tools from touching electrically hot surfaces.

I once tried to measure the 400vdc degaussing voltage on a Heathkit TV. My shoulder touched the metal TV frame, and so now I am skittish.

Also, ran my hand through a table saw, so +1 on the skittish.

Bought roof anchors, ropes/chains and a body harness so I can do roof work. +1 again.

Challenged a street punk. +1
He was found not guilty by a probably corrupt judge, so I took some time to get a black belt. Fought in tournaments. +1 for vigilant

Sometimes I wonder how much I value my life and health.
This is a calculation all of us make every day as soon as we get out of bed.
And my frau depends on my life and health, so it's not just me who has
money in this poker game.

BTW, I'm leaving the water pipe wire stub in place on the pipe for later measurements, so I wrapped tape around the pipe except where the stub is, so the steel pipe clamp does not touch the pipe copper.

But thanks for asking!!

BTW, I still have faith that the Thevenin Equivalent Circuit can reduce the entire PoCo grid down to a voltage source and a series resistor.

 

[al hildenbrand]

BTW, I still have faith that the Thevenin Equivalent Circuit can reduce the entire PoCo grid down to a voltage source and a series resistor.

I get that. I'll be curious at the approximations you choose, along the way. After one allows for the dwelling loads, including the Premises Wiring (System) itself, one is left with a current coming from other "circuits." To arrive at a reasonably accurate Thevenin Equivalent, all those other circuits must be included.

 

[gar]

201223-1501 EST

WasGSOHM:

I still go back to your first post. There insufficient information to determine direction of power or energy flow.

Your post #12 changed the information you are working with.

Consider the following experiment:

You and your meter are inside a block box. You have no knowledge of what the circuit is outside of the box. A single wire passes thru this box. Your meter happens to be a clamp-on type for both AC and DC current measurement. You also have two or three or more bare spots on the wire between which you can measure voltage drop. For the purpose here the wire is a pure resistance, no inductance. Thus, both voltage and current measurements are in phase.

The results will be the same whether the experiment is done with AC or DC current in the wire.

There is insufficient information for you to determine the direction of power flow.

Now suppose the wire points where entry and exit of the box occur are labeled X1 and X2, and source voltage, and load outside the box makes X1 more positive than X2, then by current direction in the wire inside the box, you have no way of knowing whether power flow is from X1 to X2, or X2 to X1. More information is needed.

If you can open the circuit, and measure the voltage, then you can get the additional information.

In your post #25 you have changed the circuit.

"I disgree with the two resistor statement; if you pass current through Romex and measure the voltage drop along one line, you can tell which outlet is upstream of which other (like for determining where to place a GFCI."

Post #25 is different than post #1. In this case, #25, you know where the load and source are. Thus, voltage drop does provide direction of power flow. This experiment is useful if you have a number of outlets distributed along a branch circuit. Suppose you put a 1500W heater on one mid circuit outlet. Now measure voltage drop from the source to various outlets. There will be increasing voltage drops relative to the main panel as you go from one outlet to the next along the branch circuit, but no more change in drop as you pass the load point. This is a way to determine the ordering of the outlets along the circuit.

.

 

[WasGSOHM]

201223-1501 EST

WasGSOHM:

I still go back to your first post. There insufficient information to determine direction of power or energy flow.

Your post #12 changed the information you are working with.

Consider the following experiment:

You and your meter are inside a block box. You have no knowledge of what the circuit is outside of the box. A single wire passes thru this box. Your meter happens to be a clamp-on type for both AC and DC current measurement. You also have two or three or more bare spots on the wire between which you can measure voltage drop. For the purpose here the wire is a pure resistance, no inductance. Thus, both voltage and current measurements are in phase.

The results will be the same whether the experiment is done with AC or DC current in the wire.

There is insufficient information for you to determine the direction of power flow.

Now suppose the wire points where entry and exit of the box occur are labeled X1 and X2, and source voltage, and load outside the box makes X1 more positive than X2, then by current direction in the wire inside the box, you have no way of knowing whether power flow is from X1 to X2, or X2 to X1. More information is needed.

If you can open the circuit, and measure the voltage, then you can get the additional information.

In your post #25 you have changed the circuit.

"I disgree with the two resistor statement; if you pass current through Romex and measure the voltage drop along one line, you can tell which outlet is upstream of which other (like for determining where to place a GFCI."

Post #25 is different than post #1. In this case, #25, you know where the load and source are. Thus, voltage drop does provide direction of power flow. This experiment is useful if you have a number of outlets distributed along a branch circuit. Suppose you put a 1500W heater on one mid circuit outlet. Now measure voltage drop from the source to various outlets. There will be increasing voltage drops relative to the main panel as you go from one outlet to the next along the branch circuit, but no more change in drop as you pass the load point. This is a way to determine the ordering of the outlets along the circuit.

.

We might be in violent agreement.

 

[WasGSOHM]

I get that. I'll be curious at the approximations you choose, along the way. After one allows for the dwelling loads, including the Premises Wiring (System) itself, one is left with a current coming from other "circuits." To arrive at a reasonably accurate Thevenin Equivalent, all those other circuits must be included.ut

Now I'm down to 1.46 mV with load changes at my end.
My clamp on still doesn't register the 0.2A and it should. And auto correct won't let me type "clamp on" as one word.

If I mike the wire diameter I can get a better fix on the wire resistance; it looks like copper.
I'll try at 11 PM to see what mV values I get.

So far it's looking like most of this is from the neighbors. With enough samples over random times of day and night, I can subtract out these guys to some level of certainty.

I have some of the I, and the rheostat procedure should give
me the V and the series R in the circuit model.


BTW, I inherited a digital micrometer that runs on a button cell - these tiny cells make the thing more marketable but it eats cells. And if you rotate the cell it works again so maybe there's a contact resistance problem, made worse at this voltage and low current levels.

So now I have an AA cell wired externally. High contact force in the holder.
Ugly, but it keeps on going, and I should get shelf-life lifetimes out of this battery.

Haven't had this much fun since I stuck a magnet in a light socket to make it stronger, back when I was wee lad.

 

[WasGSOHM]

You sure you have 120/240 and not two the same phase and a neutral?

13+9= 22 and is exactly what you should have if it is two of same phase and a common neutral.

Yeah, it's 240 center tapped.

 

[WasGSOHM]

Throughout the day the ground wire current went from 0.23 to 0.11 A.
If you assume a V of 120 this gives a closed loop resistance of 1/2 to 1K.

What voltage may I expect between the utility pole ground rod and my panel ground?

I'm still working on some way to open the ground at the panel and check the V across the gap. The TelCo depends on keeping the water pipe ground connection.

 

[hbiss]

The TelCo depends on keeping the water pipe ground connection.

How is that?

-Hal

 

[kwired]

How is that?

-Hal

Probably by bonding to nearest water pipe. Unfortunately I've seen them bond to an outdoor sill cock yet interior piping is non metallic.
Of course we supposed to have an intersystem bond terminal for them now. But they are clueless and will run right past it to get to something else they think they need to connect to. Same for many CATV or satellite TV installers.

 

[WasGSOHM]

Probably by bonding to nearest water pipe. Unfortunately I've seen them bond to an outdoor sill cock yet interior piping is non metallic.
Of course we supposed to have an intersystem bond terminal for them now. But they are clueless and will run right past it to get to something else they think they need to connect to. Same for many CATV or satellite TV installers.

It goes to a fat copper clamp tap on the same #8 ground wire.

Disconnecting this #8 in the panel is too messy so I might run another ground wire to the pipe just to keep the TelCo happy, and then loosen the existing pipe clamp.
Then use my pigtail wire/hose clamp arrangement to measure the V to the now disconnected panel ground. I'll start with the 750v range.
I'll have to write a procedure to keep this straight.

The utility pole woven 1/4" metal rope is covered by a
C-shaped wooden sleeve that has long ago gone to splinters.
I already wrote PepCo about a climbing spike that was at eye level, but they can figure this one themselves.
After I connect my 100' voltmeter lead.

BTW, there is another uninsulated 1/4" bundle of #14s in the panel going to the ground busbar but the source disappears in the wire clutter. What might this come from? It doesn't leave the panel. It's not the 1/2" thick service neutral.