Electrons

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Karl H

Senior Member
Location
San Diego,CA
I would like to ask the wise people of this forum for clarification,dealing with Grounding/Bonding.
Electrons leaving a power supply are always trying to return to the same power supply.
Take a separtely derived system,Ie. 3 phase transformer.
The electrons leaving Phase A,B,and C hopefully, thru a compliant pathway
will return to XO. We provide a low-impedance fault-current path for all metal conductive materials back to XO to clear a ground fault by lowering the resistance of the current path so that the fault current can be elevated to a high enough level that will trip or blow the OCPD as quick as possible.
We are required to Ground Xfers according to 250-52.So if we bond the water pipe and or structural steel.Arent we just providing a low-impedence path to XO incase of a ground fault or objectional current on the pipe or steel?Not Grounding but Bonding or is it both? So if electrons are always trying to return to the source and not to earth.Why do we Earth? Are ground rods at services just for lightning or utility faults and not to clear ground fault currents on the premises systems? I'm old school we used to ground,Now we Bond and Ground. Now, my friend says;" Visualize electron flow!" Is it because of my stupidity why my head hurts? lol
Thanks Guys
 

mdshunk

Senior Member
Location
Right here.
Among the couple reasons to earth is to give a lightning strike an easy place to go to the earth, so that hopefully less of it will come in to blow up your equipment. Has really nothing to do with the normal function of the installed system.
 

eric stromberg

Senior Member
Location
Texas
250.4(A)(1)
Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, ...and that will stabilize the voltage to earth during normal operation.

250.4(A)(3)
Bonding of Electrical Equipment. Non-current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

250.4(A)(4)
Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.

Grounding is to connect systems to the Earth for the purposes of giving the systems a reference. Stabilizing system voltages from transients and lightning. 250.4 (A)(1)
Bonding is to establish a low-impedance path back to the source for tripping overcurrent protective devices such as circuit breakers or fuses in order to reduce the possibility of touch-potential. 250.4(A)(3)

:cool: :smile:
 

eric stromberg

Senior Member
Location
Texas
250.2 Definitions

Effective Ground-Fault Current Path. An intentionally constructed, permanent, low-impedance electrically conductive path designed and intended to carry current under ground-fault conditions from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground fault detectors on high-impedance grounded systems.

250.4(A)(5)
...The earth shall not be considered as an effective ground-fault current path.
250.4(B)(4)
...The earth shall not be considered as an effective ground-fault current path.
250.54
...but the earth shall not be used as an effective ground-fault current path
 

stickboy1375

Senior Member
Location
Litchfield, CT
eric stromberg said:
250.4(A)(1)
...and that will stabilize the voltage to earth during normal operation.

So it will be unstable during normal operation with out ground rods? :roll:

I never understood what the heck they are talking about with that statement..:-? Any hints appreciated...
 

Karl H

Senior Member
Location
San Diego,CA
I've memorized the "Code" reffrences.I would like a better description or any for that matter.Why do we "Earth" to stabilize voltage?What does that mean?
I understand clearing fault current or objectionable current.My buddy is on my S...List for making me now think about electrons instead of life safety.lol
 

sparky_magoo

Senior Member
Location
Reno
stickboy1375 said:
So it will be unstable during normal operation with out ground rods? :roll:

I never understood what the heck they are talking about with that statement..:-? Any hints appreciated...
I read the ECM segment about grounding an bond. It took place over several issues. I kept the magazines. Mike also had a grounding/ bonding thing going on this website. No surprize, Mike probably wrote the ECM stuff.

Mike had a grounding/ bonding test I took online and failed miserably. I took the test over and over until I could ace it.

Now, what is this about? Does a ground rod stabalize voltage? I used to believe this.

I am a product of the eghties, where isolated grounds reined supreme.

Mike broke thoses myths I held on so dearly to.
 

mdshunk

Senior Member
Location
Right here.
Karl H said:
.Why do we "Earth" to stabilize voltage?What does that mean?
It MIGHT help stabilize the voltages a tiny bit during certain failure conditions, like an open or loose utility neutral. A municipal water pipe GEC will certainly have this effect, but a driven ground probably won't very much. That's my best stab at a guess about what they mean by "stabilize". Other than that, I think it's confusing language that needs removed from the corpus text.
 

eric stromberg

Senior Member
Location
Texas
stickboy1375 said:
So it will be unstable during normal operation with out ground rods? :roll:

I never understood what the heck they are talking about with that statement..:-? Any hints appreciated...
Not necessarily. I suppose you could think of the GEC as a sort of "bungie cord" that keeps tension on the system. If there are stimuli that are stronger than the bungie cord, they will stretch the cord.

Even in an ungrounded system (like a delta/delta), the system is 'centered' by the capacitance of the cables. A very weak 'bungie' cord. It doesn't take much to cause this system to drift off of center. I have heard a description of a transformer secondary as being a 'bead on a string.' I like this picture. The secondary can move around to wherever you want it. You have a 120 Volt secondary? Ok. Connect one side to the Earth and call it Zero volts. The other side will be 120V. If you have a 1400 volt system nearby, you could connect one side of your 120V transformer to the 1400 Volts and the other side would either be 1520 Volts or 1280 Volts, depending on how it was connected. The point is, the only thing you really know about the transformer secondary is that there are 120 Volts across the windings. How you connect it determines everything else. One of the things you have to be careful about, however, is the insulation rating of the conductors. Consider a typical Neon sign transformer. These might have a 12,000 Volt (or 15,000 Volt) secondary. The insulation of the conductors, however might be 7.5kV or 8kV. If you connected one end of the secondary to Earth, you would have a transformer with 0 and 12,000 Volts on the secondary. This would require you to have 15(or so)kV insulation. If, on the other hand, you have a center-tap on the secondary and connect it to Earth, you now have 6000 Volts on each end, with respect to Earth (Zero Volts). Easily within the rating of 7.5kV insulation.

Ungrounded systems can build up static charges (e.g. from lightning strikes nearby) and can drift off center. They can drift enough to cause the insulation rating of one of the conductors to be exceeded and can result in arcing through the insulation. Connecting the system to the Earth gives this build-up of static charges a path to the Earth and results in a 'stabilized' system.
 

Karl H

Senior Member
Location
San Diego,CA
Ok in my understanding the Utility provides multiple ground refrences "Ground Rods" along there system for voltage drop,open neutral,short ckt. etc..But,how does "Earthing" stabilize a customers voltage supply? When the Utilities do that for us?480 208 systems on customers side.I'm not talking about grounding a 12000v customer owned substation.Wich i've done 4 times but under direction of the utilites company.Am i even close to being correct about Electrons returning to there power supply and not the earth.If so i dont see the purpose of Earthing but i do see how important Bonding is.I'm talking about Earthing private systems not utilities over long distances.Was'nt the Uffer Ground invented because of lightning strikes to ammo dumps in AZ?
 

sparky_magoo

Senior Member
Location
Reno
Karl H said:
Ok in my understanding the Utility provides multiple ground refrences "Ground Rods" along there system for voltage drop,open neutral,short ckt. etc..But,how does "Earthing" stabilize a customers voltage supply? When the Utilities do that for us?480 208 systems on customers side.I'm not talking about grounding a 12000v customer owned substation.Wich i've done 4 times but under direction of the utilites company.Am i even close to being correct about Electrons returning to there power supply and not the earth.If so i dont see the purpose of Earthing but i do see how important Bonding is.I'm talking about Earthing private systems not utilities over long distances.Was'nt the Uffer Ground invented because of lightning strikes to ammo dumps in AZ?
I thought it was NM.
 

Karl H

Senior Member
Location
San Diego,CA
I think you're right. I just remember a desert so the first thing that came to mind was AFRICA.But, it was in the USA so it had to be AZ that's the closest desert i know lol
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
There is a reasonable explanation for the notion of a ground (earth) connection stabilizing the voltage on a power system. But I have to run off shortly, and don't have time just now to write it up. I'll get back to you on this.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
I wrote this up some time ago, in response to a question about the purpose for ground rods and the manner in which they “stabilize the voltage to ground.” I wanted to write this for an audience with no formal training in electrical engineering concepts. Unfortunately, as a result I was not able to give a short answer. So bear with me, if you will.

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Voltage is the difference in “potential” between two points. “Potential” can only exist in the presence of an electric field. Suppose you had in your hand a charged object (i.e., metal ball to which a charge had been applied and that you hold with insulating gloves). Suppose you are surrounded by an electric field (the source of which need not be known, so let’s just assume it is there). Finally, suppose you intend to walk across the room, while holding the charged object. Depending on the orientation of the field (i.e., which way is Plus and which way is Minus), and depending on the nature of a packet of charge (i.e., again, whether it is plus or minus), the field will either help you by pushing the charge in your direction of travel, or it will fight you by pushing it in the other direction. Some amount of energy will be needed, in order to move this charged object through the field. The notion of “voltage between two points,” or “potential difference between two points,” has to do with the amount of energy it takes to move a charge from one point to the other.

“Potential” is a bit of an obscure concept. But you can look at it like this.

Suppose we live in separate houses on the same road. It is a very, very long road, and it is straight and level. There are no turnoffs available, no intersections of other roads. There is a town somewhere way, way beyond your house. I am not going to tell you the name of the town, nor how far that town is from your house. Suppose that if a car started at “that town” and drove to your house, it would take 70 gallons of gas for the trip. Suppose that if the same car driving the same way under the same conditions drove from “that town” to my house, it would take 90 gallons of gas to make the trip. Can you tell me how much gas it would take for that car to go from your house to my house? Did you guess “20 gallons”? Did you need to know the location of “that town,” in order to arrive at your answer?

Now suppose there is an electric field in the vicinity of our two houses and all along the road. Suppose someone wants to move a packet of charge (let’s say it is one coulomb of charge) from “that town way, way over there” (the usual engineering term for this is “from infinity”) to your house. Let’s ignore the gasoline needed to move the vehicle that distance, and only look at the extra energy needed to move a charge that distance in the presence of the electric field. It will take some amount of energy to make that trip. Let’s say it took 70 joules of energy. Suppose instead they moved the same amount of charge from “that town way, way over there” to my house, and it took 90 joules of energy to make the trip. Can you tell me how much energy it would take to move the charge from your house to my house? Did you guess “20 joules”? Did you need to know the location of “that town,” in order to arrive at your answer?

So then, what is the voltage between your house and mine? It is a difference in potential of 20 joules for every coulomb of charge you try to move from your house to mine. A “Volt” is defined as “one joule per coulomb.” Thus, the voltage between your house and mine would be twenty volts.

Now to the question of how a ground rod “stabilizes” a power system. Consider first an ungrounded system (i.e., no ground rods). The Equipment Grounding Conductors are bonded to the neutral conductors (can’t call them “grounded conductors”) at the main service point. But that point is not connected (via a Grounding Electrode Conductor) to planet Earth.

Consider a coffee pot on the kitchen counter. It operates at 120 volts. Consider the wires that enter the coffee pot. If there are 120 volts between the hot conductor and the neutral conductor, then what is the voltage between the hot conductor and planet Earth? While we’re at it, what is the voltage between the neutral conductor and planet Earth? These are like asking the distance from “that town” to your house, or the distance from “that town” to my house. The answer is that you don’t know. And as far as a light bulb, a TV set, or our coffee pot are concerned, it does not matter. You could have a voltage of 1,120 volts from the hot wire to planet Earth, and a voltage of 1000 volts from the neutral wire to planet Earth, and the difference is still 120 volts, so therefore the coffee pot will work properly.

So why is this a problem? Because the internal wiring of the coffee pot is designed to stop current from leaking from the energized parts to the outside world, provided that the voltage between the energized parts and the planet is not over 600 volts (the standard insulation rating for most of what we deal with). But in my example, the voltage is almost double the insulation’s rating. That would not be safe. You could get current leaking from the internal wires to the outside of the coffee pot.

There is another reason that this situation would not be safe. This time let’s presume the insulation system does its job, and there is no leakage current from the internal wires to the outside case. You normally think it to be safe to touch the metal outer case of the coffee pot. But is it safe? What is the voltage between the case and planet Earth (the planet by the way to which your feet are attached at the moment)? Well, there was 1120 volts from hot to ground, and 1000 volts from neutral to ground, and the neutral wire is attached (at the service) to the EGC, and the EGC is attached (internal to the coffee pot) to the external case of the coffee pot, so my guess is that there would be close to 1000 volts between the case (to which your hands are attached) and the planet (to which your feet are attached).

How do we stop that from happening? By connecting the neutral wire (at the main service) to planet Earth. That causes the voltage at the neutral and the voltage at the dirt to be almost the exact same value. That in turn causes the voltage between the hot conductor and planet Earth to be no more than about 120 volts. There may be some variation from moment to moment. But the voltage rating of the insulation systems of household electrical appliances will not be exceeded. In addition, the voltage between your hands and your feet, as you touch the external metal parts of kitchen appliances, will be close to zero at all times.

It is in this sense that the voltage has been stabilized.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
stickboy1375 said:
So it will be unstable during normal operation with out ground rods? :roll:

I never understood what the heck they are talking about with that statement..:-? Any hints appreciated...
I will take a stab at this. The earth bond stabilizes the voltage because it shorts out the capacitance between the conductor and earth. Otherwise you would hav an LC circuit formed by the conductor which can cause a "RINGING EFFECT" that detoriates the cable insulation and components of the systems. By bonding to earth shorts out the capacitance thereby removing it from the circuit.
 

72.5kv

Senior Member
You took the words right out of my mouth Dereck. One former EE professor explained to us that in essence there is no such thing as an ungrounded system. There is always the effects of coupling capacitance between the conductors and the earth. Voltage on an ungrounded system and the earth can be anywhere between 0 to several kilovolts thus placing alot of stress on the insulation. Also to minimize damage from lightening.
 
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Karl H

Senior Member
Location
San Diego,CA
Charles,
My hat is off to you sir.I might even bow .lol Thank you so much for your time,effort and explanation of one of the mystries that have eluded me for years.I'm a "By the rules" kind of guy.If the "Good Book" says,to do it, i do it to my understanding of the letter.But, i'll secretly obsess over the Why's,explanations,and mathmatical results.lol I've printed this out.I'll be reading your explanation every morning,break,during lunch in my truck,after work(when i should be mowing the lawn),I might even ask my wife to read this to me as a bedtime story.Until,i understand every word you said.lol
Thank you so much sir.
PS
After achieving "RainMan" status in regards
to your explanantion.I'd like to talk about
Electron Flow,and Electromagnetism etc...
lol
 

macmikeman

Senior Member
So now I have a question about some of the above explanations, since I am not an engineer and have not had the training in the higher voltage systems up above 600 volts. I have an ungrounded seperatly derived system installed in my house called a doorbell circuit. It runs off of a transformer that delivers what I thought to be approx. 16 volts ac across the two conductors. Are we now telling me that with respect to the land under my feet, the conductors could be possibly in the kilovolt range at times since it has no connection whatsoever to the grounding electrode conductor?
 

Karl H

Senior Member
Location
San Diego,CA
Ok Mac this is a very dangerous system.We are talking 16v here! So i would recommend running a 500kcmil conductor to the nearest grounded water pipe.Now make sure that the water pipe is uncovered or exposed it's entire length.Ok let's stay on the side of caution here. A 16V arc flash could exceed
50 degrees F.So i would recommend 12KV PPE's.Plus have your wife or friend ready with 911 on speed dial in the case of emergency.Please i beg you! Turn off the Main before making your connection to the Xfer using a listed bonding lug!Also, after turning off the power supply.Be sure to check the CKT with a 12KV rated Inductive Voltage Meter(Hot Stick)to ensure the power supply is in the open position. Good Luck Fella!!!! lmao:grin:
 

macmikeman

Senior Member
That was a nice funny answer Karl, but it only skirts the issue. My question was not posed since I thought there might be some real problem with the 12 volt system, but rather to provoke some logical answer since what I question is no different than Charlie's coffee pot at 120 volts. The fact is that I am skeptical by nature of any electrical theory that applies itself to one voltage but not the other. In other words, show me some tangible difference or I will be forced to condemn the whole connection to earth theory as gobbledygook.
 
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