Grounding VS Bonding

[GoldDigger]

Maybe, maybe not.
I'd like to think that I am doing those things. I follow the rules I've been taught. But it still doesn't mean I understand all of the reasons why.
The quote I replied to said this "the "EGC" is serving more than one purpose - it is fault clearing AND connecting equipment to earth." I don't understand at all the earthing part. As I understood it (until now) the EGC was to carry fault current back to the neutral buss, which is in turn connected to earth via the GEC thru the water service which is connected to earth. The current would flow thru the earth to the wire that runs up the side of the utility pole.
Please correct all that you see fit.
Thanks
Mike

I will make one correction, and leave any more for others.

In the case of a fault from hot to some exposed metal connected to the EGC, the fault current will follow the EGC back as far as the main panel where the EGC is bonded to the service neutral and will follow that path back to the X0 terminal of the POCO transformer. Some small portion of that may instead follow the earth-based path you describe.

Only if the POCO neutral is compromised will all of the current be forced to go via the earth either to the POCO ground rod or more likely to the working utility neutral attached at another nearby house on the same water supply or other common ground electrode.

 

[electrofelon]

Maybe, maybe not.
I'd like to think that I am doing those things. I follow the rules I've been taught. But it still doesn't mean I understand all of the reasons why.
The quote I replied to said this "the "EGC" is serving more than one purpose - it is fault clearing AND connecting equipment to earth." I don't understand at all the earthing part. As I understood it (until now) the EGC was to carry fault current back to the neutral buss, which is in turn connected to earth via the GEC thru the water service which is connected to earth. The current would flow thru the earth to the wire that runs up the side of the utility pole.
Please correct all that you see fit.
Thanks
Mike

Look at 250.4(A) 2008 code. It lays out the three things that "grounding" generally refers to and describes what each accomplishes - in theory. I would like to elaborate on several with my opinions. There may be different opinions out there.

System grounding. the two major benefits of system grounding are: 1) if i high voltage line falls on your overhead service drop's neutral and the high voltage system is a grounded system, the earth will be a fault path back to the source (due to the very high voltage) and trigger a utility OCPD. If this were to not happen, almost every metal thing in the structure would be raised to thousands of volts. 2) grounded systems are more idiot proof when it comes to faults because the system will not function after a fault until the problem is fixed where ungrounded systems require monitoring and will keep functioning after the first fault. "limit voltage imposed by line surges" and "stabilize the voltage to earth" are kinda BS or misleading

Equipment earthing is not very important and generally doesnt do much, nonetheless it is required.

It is bonding that is really important - connecting everything conductive together so everything remains at the same potential.

So think of these three things - system grounding, equipment grounding, and fault clearing - and think about the EGC, the main bonding jumper, and the GEC, and you will see that each are doing two jobs (assuming a grounded system).

 

[ActionDave]

Maybe, maybe not.
I'd like to think that I am doing those things. I follow the rules I've been taught. But it still doesn't mean I understand all of the reasons why.
The quote I replied to said this "the "EGC" is serving more than one purpose - it is fault clearing AND connecting equipment to earth." I don't understand at all the earthing part. As I understood it (until now) the EGC was to carry fault current back to the neutral buss, which is in turn connected to earth via the GEC thru the water service which is connected to earth. The current would flow thru the earth to the wire that runs up the side of the utility pole.
Please correct all that you see fit.
Thanks
Mike

I agree with Gold. Omit the earth connection and if everything else is correct a fault will clear. Otherwise I see things the way you do.

I have heard of things like capacitance and transients as reasons to connect to earth. I let the guys with capital letters after their names worry about that.

 

[mike1061]

Only if the POCO neutral is compromised will all of the current be forced to go via the earth either to the POCO ground rod or more likely to the working utility neutral attached at another nearby house on the same water supply or other common ground electrode.

I meant that, I just forgot to type it. Sorry.
Thanks
Mike

 

[mike1061]

Look at 250.4(A) 2008 code. It lays out the three things that "grounding" generally refers to and describes what each accomplishes - in theory. I would like to elaborate on several with my opinions. There may be different opinions out there.

System grounding. the two major benefits of system grounding are: 1) if i high voltage line falls on your overhead service drop's neutral and the high voltage system is a grounded system, the earth will be a fault path back to the source (due to the very high voltage) and trigger a utility OCPD. If this were to not happen, almost every metal thing in the structure would be raised to thousands of volts. 2) grounded systems are more idiot proof when it comes to faults because the system will not function after a fault until the problem is fixed where ungrounded systems require monitoring and will keep functioning after the first fault. "limit voltage imposed by line surges" and "stabilize the voltage to earth" are kinda BS or misleading

Equipment earthing is not very important and generally doesnt do much, nonetheless it is required.

It is bonding that is really important - c8onnecting everything conductive together so everything remains at the same potential.

So think of these three things - system grounding, equipment grounding, and fault clearing - and think about the EGC, the main bonding jumper, and the GEC, and you will see that each are doing two jobs (assuming a grounded system).

2) grounded systems are more idiot proof when it comes to faults because the system will not function after a fault until the problem is fixed where ungrounded systems require monitoring and will keep functioning after the first fault.


It is bonding that is really important - connecting everything conductive together so everything remains at the same potential.

Those two parts I already understood.

Equipment earthing is not very important and generally doesnt do much, nonetheless it is required.

This is the one I don't understand at all.

1) if i high voltage line falls on your overhead service drop's neutral and the high voltage system is a grounded system, the earth will be a fault path back to the source (due to the very high voltage) and trigger a utility OCPD. If this were to not happen, almost every metal thing in the structure would be raised to thousands of volts.

This one I never thought of, but it makes perfect sence.
I'll re-read this later.
Thanks
Mike

 

[jcassity]

You were talking about the confusion so I mentioned where a lot of the confusion comes from. In electronics chassis grounds are also used adding to the confusion
.

No Sir! ~that actually solves it.

i highly disagree.
From my many years in avionics, the Navy Neets manuals solve all this confussion. I run into so many people who cant separate the concepts of this thing called <insert term here>.

I have to agree somewhat way back with electronfelon that we are talking about 3 different things but i am able to process Two catagories.

Its my belief and with the influence of my aviation electronics training, and now in communication facility powering that we can more easily call it two things...

Circuit Ground
~every circuit has a "circuit" ground conductor or path.

Chassis ground
~everything we deal with that moves electrons has a chassis/enclosure holding all the parts together and we are all smart enough to know metalic from non metalic

my implied third term would have been "return" conductor but in the low voltage high amperage DC power system designs, this may need to be avoided since all our "return" conductors have current.
We also in large DC power plants have something called "Reference Ground..... so in my opinion the two options i call out above will satisfy low voltage installations somewhat yet with uniqueness dedicated to this area.

in the AC world, chassis ground vs circuit ground more clearly identifies where you are in the schematic.
In my engineering scopes, i use the two terms all the time and our contractors get it when its worded that way.


doing it this way clealy opens the door to terminology like "ground field" "ground electrode" "ground ring" ect ect

 

[jcassity]

Now I am getting confused so this renaming is just not going to work. Ground, grounded, grounding all imply a connection to earth. Ground fault implies that a fault has occurred to earth.

The definition of ground, past, present, or future is earth. I remember this as a kid. Mom would say, "get up off that wet ground before I whip your butt."


If we are to rename the EGC then we must rename the neutral as the NEC now refers to it as the grounded conductor. This in itself implies that it is connected to earth.

glad you said it that way..

System / sub system "hot Conductors" = term - "CONDCUTOR"
System / sub system "neutral conductors"= term = "Return Conductor" , aka "neutral"
System / sub system green wire (for AC applications) = term "Circuit Ground"
System / sub system chassis or enclosure = term "chassis ground"

 

[electrofelon]

Those two parts I already understood.


This is the one I don't understand at all.

Do you mean that you dont understand how earthing equipment could not be beneficial? It is a little strange to talk about earthing vs not earthing equipment on a grounded system because it happens naturally - you cant really disconnect stuff from earth, unless you are getting rid of the fault clearing system too. Thus I feel it is better to discuss this topic in regards to an ungrounded system. When you think about it in terms of an ungrounded system, I guess it makes more sense and I could see its benefit from a bonding perspective, that is its just like other bonding where you want everything conductive (here we are calling the dirt conductive) connected together. Say you have an ungrounded system (and remember this means the system is not grounded, not that equipment is not grounded/earthed). In a perfect world, there would be no voltage between the ground and any raceways or equipment. However its not a perfect world and we have less than perfect insulation, induction, capacitance.....which could result in potential between a raceway and the ground. Presumably these current would be very low so the potentials would be equalized fairly well even distant from the grounding electrode - unlike a high current where the earth to raceway potential will be similar only very close to the grounding electrode. I welcome any corrections, disagreements, additions....

 

[mike1061]

Well say you had an ungrounded system. The only one I've ever seen was a 3? 240 volt system. Lets use that as the example. 3 hot wires and no neutral or ground (that I saw). It was a small industrial building of some kind.
So you are saying it should/could be connected to earth? I would think that the main disconnect cabinet should be connected to the water service. What if they have no water service? Would you then drive a rod into the earth? Would that be earthing or grounding?
Thanks
Mike

 

[electrofelon]

Well say you had an ungrounded system. The only one I've ever seen was a 3? 240 volt system. Lets use that as the example. 3 hot wires and no neutral or ground (that I saw). It was a small industrial building of some kind.
So you are saying it should/could be connected to earth? I would think that the main disconnect cabinet should be connected to the water service. What if they have no water service? Would you then drive a rod into the earth? Would that be earthing or grounding?
Thanks
Mike

So just to make sure we are on the same page, "system grounding" is when one leg of the power supply is connected to earth giving that conductor the same potential as earth. Connecting equipment to earth and bonding things back to the source for fault clearing are totally different things. An ungrounded system is required to have a grounding electrodes system just like a grounded system, but it used only to connect equipment to earth and not one leg of the system to earth - all of the conductors of the system "float" and are not connected to the GES. So yes as you say the disconnect cabinet would connect to the grounding electrode conductor and you would have to connect to any grounding electrodes that are present and if none are then you have to make them which is usually two ground rods. According to the NEC article 100 definition, this would be equipment grounding. Note the FPN under the definition of "grounding conductor, equipment" which states that "it is recognized that the egc also performs bonding" That gets back to when I was talking about the dual role of the EGC. IT is not always clear in the NEC which type of grounding they are talking about. For example look at part VI of article 250, "equipment grounding and EGC's". According to the definitions and description in 250.4(A)(2), this section is concerned with connecting equipment to earth. Do you really think that is the sole intent of this section is connecting equipment to the earth? They are discussing bonding too, or that is when they mean. It says right in 250.110 "...equipment likely to become energized..." which means they are talking about bonding back to the source to clear a fault as connecting a energized piece of equipment to the earth wouldnt do much. I guess it is that FPN that saves the day and makes this not a glaring error, but IMO still confusing.