Typical current flow to a U.S. residential ground spike?

Thread Starter

wayneh

Joined Sep 9, 2010
16,154
If I could watch the current going to ground at my ground spike, what would I see? If the system operates normally, should there be any significant current there? (Let's say anything >1A = significant.)

Wouldn't my system work OK (until something bad happens) without the ground spike, and it's just there for safety reasons?

Hypothetical questions, BTW.
 

MaxHeadRoom

Joined Jul 18, 2013
19,669
You may not see any significant difference, some effects are caused by typical 'leaky' kind of appliances etc, and in that case you could experience a slight tingle if the ground conductor was absent, which would normally flow back through ground, but not large enough current to blow a fuse or breaker.
A large number of household items now are no longer fitted with a earth wire/ground reference, most electronics, even kitchen appliances such as kettles, coffee pots, irons etc.
Most that ARE fitted with a ground are power tools etc.
Particularly items that can be used outside (wet) and are typically used on a GFI circuit.
Max.
 

#12

Joined Nov 30, 2010
18,167
Illegal splice.png The theoretical answer is, "zero". There is a good, solid wire from the center tap of the transformer on the pole to the ground/neutral bus in your home. If there was no earth ground at the transformer pole and there was no connection to the water pipes next to the watt-hour meter box, the answer would always be zero. Thus, you have to consider the path through the soil as a parallel path in shunt with milli-ohms. Consider #4 AWG copper at 4023 ft/ohm. No way that transformer is 8 blocks away! Probably less than 402.3 feet.

So, what path in parallel with 1/10th of an ohm carries an amp? You would need 10 amps to develop a volt across that 1/10th ohm neutral wire. What current will 1 volt drive through a hundred feet of soil? Not very much.

The presence of measurable current in the earth ground is a dead giveaway that something is wrong with the neutral wire. That happened at my house. Seven amps going through the earth ground led me to find an illegal splice in the neutral line from the meter to my breaker box.
 
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MaxHeadRoom

Joined Jul 18, 2013
19,669
The presence of measurable current in the earth ground is a dead giveaway that something is wrong with the neutral wire. .
I would have to dispute that, if the CT of the transformer is grounded as it should be.
You do not show the grounded CT of the transformer, also most underestimate the current capability of earths conduction.
I can pass several amps through ground with neutral having nothing to do with it.
Max.
 

Thread Starter

wayneh

Joined Sep 9, 2010
16,154
The theoretical answer is, "zero". There is a good, solid wire from the center tap of the transformer on the pole to the ground/neutral bus in your home. If there was no earth ground at the transformer pole and there was no connection to the water pipes next to the watt-hour meter box, the answer would always be zero.
Makes sense. Any net current to ground before your meter would be a loss to the power company, and they're not known for losing much of the power they make, if they can avoid that.
 

RichardO

Joined May 4, 2013
2,271
I believe that some switching power supplies have caps from the hot to safety ground to reduce conducted noise into the power wiring. These caps appear as leakage current to the safety ground. That said, I doubt that all the electronic devices in your house add up to more than a few tens of milliamps in the safety ground wiring.

Real life safety ground stories:
I went to tech school with a fellow who's wife was nearly electrocuted by a refrigerator with bad leakage to the case. He added a safety ground to the refrigerator himself so it could never happen again.

At work an engineer was showing me an outlet strip that he had modified by cutting off both of the power pins leaving just the safety ground pin on the plug. When he plugged the plug into on of the outlets of the strip and turned it upside down the plug would fall out just from the weight of the cord. :eek:

He had been shocked by a piece of test equipment that had some leakage and found out the outlet strip it was plugged into did not protect him. I believe that the outlet strip was UL approved but none the less it had worthless safety ground pin contacts. :(

I forget the details of how UL tests the safety ground but it is something like they apply hundreds of amps from hot to the safety ground and test to see if it conducts the current long enough to trip a standard 20 amp circuit breaker. Obviously the outlet strip failed this test miserably.
 

#12

Joined Nov 30, 2010
18,167
You do not show the grounded CT of the transformer,
I fixed the drawing.:p
I can pass several amps through ground with neutral having nothing to do with it.
Please elaborate as to the current path. Please educate me as to the conductance of 100 feet of soil. Please describe how much current would flow if you applied 1 volt RMS AC in your test.
Not easy because soil conductivity varies a lot because moisture content, nature of the soil. Florida sand is a prime example of having different conductance after 4 months of "dry season" and the torrential, daily rains during the summer. Other places have loam with a noticeable carbon content.
 

MaxHeadRoom

Joined Jul 18, 2013
19,669
Your service, if it has an earth grounded neutral at the distribution transformer does not necessarily require that the local earth ground at your residence be connected to neutral.
In fact some jurisdictions in the world do not use this method but rely on a ground path back to the supply transformer ground, this is verified with a ground resistance measurement.
Although in N.A. it is usually connected/commoned at the service panel.
One excellent source of Grounding is the book by Eustace Soares which is published by the IAEI and is a world reference used by NEC/CEC.
Max.
 

#12

Joined Nov 30, 2010
18,167
I can pass several amps through ground with neutral having nothing to do with it.
You don't seem to be responding to my requests.

If I plug into a 120 VAC outlet and stab it into the planet, some current will flow because the transformer on the pole is wired to the planet. Without that intentional ground wire at one end or the other, the transformer secondary is a free floating voltage generator with no return path. Current is therefore impossible.

With an intentional earth ground at the power pole, you do have a return path. What voltage did you use to discover what amount of current which flows? Is it more likely your current experiment found the house ground with better conductance than the earth ground at the pole?
 
#12: I your case, you definitely have a loop. There's no ground rod in our house, but piping is copper and does go under the basement slab within about 15 feet. The underground portion route the water from one part of the house to another as the other path overhead is torturous. The hot water broke underground while we were on vacation. Only the hot was moved overhead.

This did create a mess for some of the new water meters because they were made of plastic. It would not in our case.

The "non-existant" spike is designed to be a reference. For telephone, for cable for electricity, for faucets, for the bath tub, the stove etc. Telco gets it ground from the same water pipe that goes underground. Again about 10' before it hits the ground,

The water services are plastic. the kitchen faucet now connects via a plastic hose. Tools are double insulated.

Ground may see leakage from the filters in a switching power supply.

The house did get one lightning strike through the roof kitchen ventilator. It took out a ground for a stove and refrigerator. It was never properly found and identified, but it was externally corrected.

Lots of work ground stories. A lot involve the ground in a single outlet in an outlet strip and computers. The ground can get energized through the leakages in the switching power supply filter and you end up with 1/2 the supply voltage to ground. Analysis shows where this can happen.

I had found a ground issue with a particular brand of duplex outlets. Possibly 420 of them in the building.
The design was such that the ground pin of the duplex was made only by pressure. Assembly tolerances of the outlet in some cases applied to little or no pressure, THUS the ground could "let go" and only connect the two devices plugged in. Thus when you had two devices plugged in and wiggled one plug, the ground COULD let go.

The "powers that be" made the decision to blanket replace the outlets in laboratory space and custodial space like hallways. Unused were left alone. Office outlets were replaced as needed. They were checked by me when computers/fax machines/copiers etc were added and replaced then.

No one wanted to replace 420 outlets and the building warranty expired. The replaced outlets were made brown and not the original Ivory.

The problem was discovered by me when the outlet took out a computer. Someone, it may or may not have been me took the outlet apart and discovered this stupid design.

I then developed a test to determine which outlets were defective. The "powers that be" didn't want to test them all either.

==

A friend had a bad splice of the power line coming into the house.

I have a rooftop antenna that is not grounded "properly" because I have not found an easy way to do it. It is grounded for static dissipation, but not for a lightning strike. I think a lightning strike would be highly unlikely because of a towering tree about 40' above the antenna. The tree should get hit first. We could consider a tree lightning rod. You talking about a 4-5 foot diameter tree about 80 foot tall.
 

MaxHeadRoom

Joined Jul 18, 2013
19,669
You don't seem to be responding to my requests.
If you don't have a qualified ground resistance back to the grounded source, pole transformer etc, then you don't have a satisfactory ground, One jurisdiction I worked in the neutral was not supposed to be connected to the local earth source.
and the service provider did not provide a earth conductor.
We had to qualify the ground by a ground resistance meter by using the neutral back to the transformer and the earth ground source loop as the circuit, this had to be lower than a certain resistance to qualify.
Regardless of the system, if you do not have this earth resistance then your earth ground is relatively useless.
Max.
.
 

#12

Joined Nov 30, 2010
18,167
If you don't have a qualified ground resistance back to the grounded source, pole transformer etc, then you don't have a satisfactory ground,
Wayneh didn't ask about legal qualifications. He asked about actual, measurable, results.
Regardless of the system, if you do not have this earth resistance then your earth ground is relatively useless.
And the result would be nearly zero current. Right? Thanks for confirming my demonstration that earth loop current is nearly zero. Now what about your statement:
I can pass several amps through ground with neutral having nothing to do with it.
Please describe the conditions and the voltage used to accomplish this.
 
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