How do I politely explain "You can't use an old 2 wire 120 VAC Run without a Ground"

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How do I politely explain "You can't use an old 2 wire 120 VAC Run without a Ground"

How do I politely explain "You can't use an old 2 wire 120 VAC Run without a Ground" to some well meaning people.

While working on some other equipment, I think I have I have stumbled upon one or two old 2 wire 120 VAC Runs with a Hot and Neutral and no Ground running through a building to a Pump and or some Light Poles.

I realize a Ground conductor should be present to carry the carry a Fault at the Lamp Pole or Pump Case back to the originating Panel Ground Bus so its Breaker will trip and personnel will be protected

I realize the Neutral is the Return Path for the Hot Conductor and goes back to the Panel to the Neutral Bus.

Unfortunately The Physics of the Panel and Breaker and how they work gets me Tongue Twisted.

Several innocent people have said with good intentions, "Why can't you just Ground at the Pump or Lamp to a Nearby Ground Rod?" At times this invites every Civil engineer and idle idiot to pipe up.

I know intuitively that you can't tie the ground conductor to a nearby Ground Rod and it has to go back to the source panel.

But how does this work? Does the Source Panel breaker somehow know that the fault has returned on its Ground Bar because the Ground Bus is to the Neutral Bus.

Exactly what happens in the Panel when that Fault comes back through the Ground conductor?
 
If there is a fault to ground, and a 3rd wire present (the EGC) the OCPD will trip. If there is not a ground wire, and there is a fault to ground, the equipment will sit at 120V and potentially shock the next person who touches it.

The 'source panel breaker' only recognizes current (eta: some recognize ground and arc faults, but many just recognize current). In the event of a fault, the EGC back to the panel completes the path and allows that breaker to trip.

While current takes all available paths back to the source, a low impedance path back to the source is what's needed to trip the OCPD. That is not a local ground rod.
 
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Simply cite 250.4(A)(5).

No more argument. Case closed.


(5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive ma- terial likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be considered as an effective ground-fault current path.
 
ActionDave said:
Explain that attaching metal light poles to ground rods does NOTHING TO MAKE THEM SAFE. What is needed is a proper Equipment Grounding Conductor back to the breaker or fuse to clear a fault and show them this graphic

View attachment 19588
Click to expand...

I like the one with the doggie better. :D



Good article for OP.


https://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/Grounding-Bonding-Poster~20030914.htm
 

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"Why can't you just Ground at the Pump or Lamp to a Nearby Ground Rod?"
At times this invites every Civil engineer and idle idiot to pipe up.

I don't mean to be disrespectful to my colleagues, but sometimes....:sick:
 
What isn't quite fully explained in the picture jumper posted is the fact that a ground rod seldom (as in almost never) has as low of resistance as an equipment grounding conductor. In that picture they show a voltage of 90 amps between the pole and "earth" and a current of 4.8 amps. 90/4.8 = 18.75 ohms. This resistance limits the amount of current that can flow. Not that earth isn't a low resistance but it is difficult to make a low resistance connection to it with just a single rod.

Run an EGC to that light pole and resistance is likely an ohm or so at the most, which will allow for much more current to flow during a fault.

you asked :But how does this work? Does the Source Panel breaker somehow know that the fault has returned on its Ground Bar because the Ground Bus is to the Neutral Bus.

it isn't that the breaker knows where that fault is returning it is just that if we insure as low of resistance path as possible for such returning current then that current will be higher - the higher the current the faster the breaker will respond to the condition.

The 18.75 ohm rod limited current to 4.8 amps - would never trip even a 5 amp fuse in that situation and leaves exposed components with voltage to "ground". Put in only a 1 ohm return path and apply 120 volts - fault current reaches 120 amps (or whatever impedance of the source will allow) easily and breaker trips almost instantaneously. The pole is still energized during that time but is a very limited exposure in comparison.
 
Installer said:
I know intuitively that you can't tie the ground conductor to a nearby Ground Rod and it has to go back to the source panel.

But how does this work? Does the Source Panel breaker somehow know that the fault has returned on its Ground Bar because the Ground Bus is to the Neutral Bus.

Exactly what happens in the Panel when that Fault comes back through the Ground conductor?
Click to expand...

Basically, when you have fault to a very low impedance path back to the source, there is a sudden very sharp rise ( to 7-30x or more of the rating of the ocpd) in current on the ckt that the fault occurred on---thus the ocpd opens very quickly, denenergizing the ckt and eliminating the danger.

The lower the impedance of a path back to the source, the more current will flow down that path.

Other members can chime in w/ a more detailed version of the physics.:)



ETA: Kwired beat me to it.:)
 
The “normal” flow of current starts at the panel, goes through the breaker, travels along the “hot” (i.e., ungrounded) conductor, to and through the load, travels along the “neutral” (i.e., grounded) conductor to the neutral bar at the panel, and at that point we can say that it has returned to its source. Now I will address your questions. Let’s say we are talking about a light pole.
Installer said:
Several innocent people have said with good intentions, "Why can't you just Ground at the Pump or Lamp to a Nearby Ground Rod?"
Click to expand...
Installer said:
Exactly what happens in the Panel when that Fault comes back through the Ground conductor?
Click to expand...
Suppose there is a failure internal to the light pole, such that a live wire comes into contact with the metal exterior parts. The current path I described above is still in effect, and the light is still operating. But now there is a second current path. It starts the same way, going through the breaker and the hot conductor. Once inside the light fixture, the current will flow along the faulted wire to the metal pole, from there to the wire you have attached to the case and also attached to the local ground rod. The current will travel along that wire, to the ground rod, into planet Earth, along the dirt to the location of the building’s grounding electrode system, into and up that system’s ground rod, up the grounding electrode conductor to the neutral bar inside the main panel, and at that point we can say that it has returned to its source. The amount of current that will flow along this path is limited by the resistance of this path. Others have already talked about this. The result is that the amount of current that this fault path adds to the total current seen by the breaker will not be enough to trip the breaker. That is why the suggestion made by the several innocent people whose intentions are good is absolutely guaranteed to fail.

It is also important to note that with the local ground rod in place, and with the fault I describe above, if a person touches the pole, it will create yet again another current path. In addition to current flowing from the metal pole to the local ground rod, current will flow through the person’s hand, along the body to the feet, into the dirt, and back to the source via the building’s ground rod. Once again, this extra current will not be enough to trip the breaker. But it will be enough to kill the person.

The only way to make this installation safe is to install an equipment grounding conductor, as others have already mentioned.

 
I'll just add that if politeness doesn't work, move on to impoliteness.
 
charlie b said:
The only way to make this installation safe is to install an equipment grounding conductor, as others have already mentioned.
Click to expand...

I have a very small disagreement with this.

IMHO a GFCI would also make this install safe, although I don't believe that such an installation would be code compliant. While a ground rod at 120V will not carry enough current to trip an ordinary breaker, it is more than enough to trip a 6mA GFCI. Probably even with a neutral to soil fault.

To the OP:

As others have noted and repeated, soil is not a good conductor and not an infinite sink for electricity. With most normal soil a ground rod will not trip a normal breaker and will not significantly reduce the shock hazard of a 120V circuit.

Because soil does conduct electricity, for higher voltage lower current circuits (eg. utility distribution circuits) the current flowing through the soil can be enough to trip breakers. I bring this up not to confuse the issue, but as a possible source of the myth that 'ground' makes things safe in lower voltage circuits. As part of a polite explanation you could even make the point that different rules apply to different situations, and that in some circumstances a ground rod would provide enhanced safety, just not this situation.

You might find some of the videos that have been posted of people running 120V from a 20A breaker to a ground rod; the breaker doesn't trip, significant 'step potentials' can be measured, and it is a great way of cooking worms up out of the ground for fish bait.

-Jon
 
winnie said:
I have a very small disagreement with this.

IMHO a GFCI would also make this install safe, although I don't believe that such an installation would be code compliant. While a ground rod at 120V will not carry enough current to trip an ordinary breaker, it is more than enough to trip a 6mA GFCI. Probably even with a neutral to soil fault.
-Jon
Click to expand...

GFCI protection would make it safer, but that is not as good as having an EGC.

Safest... overkill-both.
 
When the engineer starts to say something, take him outside stick some scrap metal into the ground about 3' apart, hook one to the hot one to the neutral turn it on. You will see worms start coming out of the ground and the breaker will not trip and you are only 3' from being able to return to the panel to trip the breaker by the neutral (grounded conductor) so how could it ever trip?
 
sameguy said:
When the engineer starts to say something, take him outside stick some scrap metal into the ground about 3' apart, hook one to the hot one to the neutral turn it on. You will see worms start coming out of the ground and the breaker will not trip and you are only 3' from being able to return to the panel to trip the breaker by the neutral (grounded conductor) so how could it ever trip?
Click to expand...

Nah, that won't convince them----they'll just say that the scrap metal isn't deep enough for the electrons to be absorbed properly...:p

Had an argument once with a guy over this.

He said that the rod did indeed trip a breaker when hit with a wire out of the panel......I called BS and asked him to demonstrate and said nothing while he did his little experiment.
And he was right!!! It sure did, b/c he had still had the #4 (GEC) connected...:slaphead::slaphead::slaphead:

I said, "ok, now lift the GEC and try it"

Him: "but I tried that and it won't trip."

Me: "Now, what does that tell you about the value of the rod??":happyno:
 
sameguy said:
When the engineer starts to say something, take him outside stick some scrap metal into the ground about 3' apart, hook one to the hot one to the neutral turn it on. You will see worms start coming out of the ground and the breaker will not trip and you are only 3' from being able to return to the panel to trip the breaker by the neutral (grounded conductor) so how could it ever trip?
Click to expand...
What "engineer" are you talking about? This is pretty simple stuff. A high series resistance is going to limit the current in a circuit. Duh.
 
ggunn said:
What "engineer" are you talking about? This is pretty simple stuff. A high series resistance is going to limit the current in a circuit. Duh.
Click to expand...

jumper said:
A civil engineer that the OP is trying to shut up about ground rods.
Click to expand...

Yeah, ggunn, right down below.:)

V V V V

Installer said:
.

Several innocent people have said with good intentions, "Why can't you just Ground at the Pump or Lamp to a Nearby Ground Rod?" At times this invites every Civil engineer and idle idiot to pipe up.
Click to expand...
 
jumper said:
A civil engineer that the OP is trying to shut up about ground rods.
Click to expand...

"Several innocent people have said with good intentions, "Why can't you just Ground at the Pump or Lamp to a Nearby Ground Rod?" At times this invites every Civil engineer and idle idiot to pipe up."

I didn't read that as him speaking to a specific civil engineer. It's a swipe at civil engineers, for sure, but I'll hazard a guess that the OP doesn't know all that much about laying out highway rights of way, either.
 
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