Purpose of Grounding Electrode System

[ActionDave]

this?

~RJ~

this

https://sites.auburn.edu/admin/facilities/spw-bid-calendar/11-150%20AU%20Regional%20Airport-Construct%20a%20Self-Supporting%20Radio%20Tower/Project%20Documents/1/Motorola_R56_2005_manual.pdf

 

[ptonsparky]

this

https://sites.auburn.edu/admin/faci...ject Documents/1/Motorola_R56_2005_manual.pdf

Ah, some light reading this evening. Thank you.

 

[romex jockey]

this

https://sites.auburn.edu/admin/facilities/spw-bid-calendar/11-150%20AU%20Regional%20Airport-Construct%20a%20Self-Supporting%20Radio%20Tower/Project%20Documents/1/Motorola_R56_2005_manual.pdf

section 4 is very specific

and this caught my eye>

• Perform a soil resistivity test at the site as described in Appendix B, “Soil Resistivity
Measurements”
• Calculate the resistance of a single ground rod as described in “Interpreting Test Results” on
page B-10.
• Determine the resistance requirement of the grounding electrode system, based on the site type
(“Light Duty” or “Standard Duty

~RJ~

 

[kwired]

Could you take an AC system, complete from generator to outlet, and have it function properly floating on a blimp, not connected to the earth?

Yes, and this is frequently done on aircraft. What you don't have with this situation is a network of conductors connecting it to other objects. Lightning striking one aircraft isn't going to send a surge of voltage through the supply network and to other objects on the network.

I think you should be careful thinking that the NEC required GES does much, if anything, to help with lightning. I think it's definitely the case that some people who've had a hand in writing the code think that. But my understanding is that in reality it's not going to help all that much.

...

By the way, the NEC allows some systems to be ungrounded by design. But those systems should still have a GES, and the NEC requires it.

A GES is not a lightning protection system, direct hit can still happen and damages from such hit can result. It can help reduce voltage rise seen at a premises when there is a nearby strike. The more structures you have between you and that strike, each with a grounding electrode, gives you more chance of seeing little to no rise on the conductors supplying your premises.

And yes even an ungrounded system still requires a GES and EGC's. EGC's are probably more important than the GES, this makes all the non currrent carrying conductive items on the premises all same potential.

 

[rambojoe]

I'm not saying there's a better way- although we've found out there is in the Norway/OR example which is expensive. I'm saying I've gotten into too many debates with electricians who think ground rods are for clearing faults or that when they get shocked it's electricity passing through them to the earth.

Electricity always returns to it's source. We bond the metal parts to neutral to clear a fault and that's usually the same reason we get shocked.

We drive ground rods for lightning.

just curious, so does this and other statements mean you are a electrical engineer? and again, this is not meant to be rude or "troll" as they say, but are you a college student? a few other things you stated made me curious...

 

[daytonajim00]

Never mind the blimp or hospital OR. lol.

The overall point is I've come across too many electricians, inspectors, and more that don't understand the purpose of the grounding electrode system. Either that or I'm wrong. So let me explain one more time.

The MBJ is responsible for carrying fault current to neutral where it wants to go (source).

The grounding electrodes are mainly for lightning, static, other foreign over voltages and to stabilize the voltage during normal conditions- though I don't understand what we are stabilizing it from.

The GEC to a water pipe is the lone wolf in that it can potentially become energized by our ungrounded conductors and that's why we size it in proportion to our service. All other connections with our GE's are usually significantly smaller because they are NOT responsible to carry a fault.

So we are 5 pages in, and it seems like many on here are endorsing the idea that ground rods have something to do with faults and/or something to do with protection from getting shocked by our system.

What's interesting is it's literally explained in one of the first NEC articles in Grouding: we make a connection to earth for lightning, static...

I think the confusion comes from the word 'ground fault'. It should be called "non-energized conductive surface fault", we should call our EGC's "equipment bonding conductors" and there should be an explanation for why we size our water pipe GEC according to service size. Grounding should be understood and treated as our connection to earth for foreign overvoltages and bonding should be our connection to all building conductive surfaces to clear faults.

 

[kwired]

Never mind the blimp or hospital OR. lol.

The overall point is I've come across too many electricians, inspectors, and more that don't understand the purpose of the grounding electrode system. Either that or I'm wrong. So let me explain one more time.

The MBJ is responsible for carrying fault current to neutral where it wants to go (source).

The grounding electrodes are mainly for lightning, static, other foreign over voltages and to stabilize the voltage during normal conditions- though I don't understand what we are stabilizing it from.

The GEC to a water pipe is the lone wolf in that it can potentially become energized by our ungrounded conductors and that's why we size it in proportion to our service. All other connections with our GE's are usually significantly smaller because they are NOT responsible to carry a fault.

So we are 5 pages in, and it seems like many on here are endorsing the idea that ground rods have something to do with faults and/or something to do with protection from getting shocked by our system.

What's interesting is it's literally explained in one of the first NEC articles in Grouding: we make a connection to earth for lightning, static...

I think the confusion comes from the word 'ground fault'. It should be called "non-energized conductive surface fault", we should call our EGC's "equipment bonding conductors" and there should be an explanation for why we size our water pipe GEC according to service size. Grounding should be understood and treated as our connection to earth for overvoltages and bonding should be our connection to all building conductive surfaces to clear faults.

The confusion is the many terms that have a common root word "ground(ed)(ing) in them, and many people thinking they all mean the same thing because of that common root word. Suggestions of using "earth" and other terms instead of "ground" IMO would still be just as confusing. One has to remember those terms are multi-word terms and you need to understand the specific definition of each one of them and not lump them all together because of a common root word.

The GEC to a water pipe is not the only one that is larger than other electrodes, so is the GEC to building steel. The reasoning isn't so much because an ungrounded conductor might contact it, but rather that water pipe and building steel typically have low enough resistance to earth that any current imposed on them can potentially be higher than the current imposed on other electrode types.

Rod and pipe electrodes only require 6AWG copper max because their resistance is never low enough that the electrode will carry more current than that size of a conductor can deliver to it. If you bottleneck a freeway down to one lane, you only get one vehicle at a time through the bottleneck even if you have 4 lanes leading up to it.

CEE's the same thing, except they have been determined to be able to carry more current as a general rule and #4 is the max size required.

 

[rambojoe]

again i hate to pry daytona... but are you a engineer? also the #6 awg keeps coming up. the table goes by largest service entrance conductor,are we not? I believe the true answer comes from why the utility xformer uses a grounding electrode...

edit- i see the jumper was refered to as #6, not the gec... anyhow...

cee? you mean egc?

 

[JPinVA]

Forget man made sources for a moment. Let's just talk the universe writ large. The universe is full of charged particles. They are in space. Around planets. In orbit. In the clouds. The air. The ground. In us!!! EVERYWHERE. We live...indeed our very universe of existence...is a cauldron of particles...many with net charges.

Like charges repel. Opposite charges attract. Charges build up on your body..or your desk...or house. As long as these charges build up together...or are able to equalize in an orderly fashion...we don't even know they are there. But let these charges build up in two different places...and then bring those places close enough then...zap!!!! This happens when you walk across a carpet in winter...and touch that door knob. Painful sometimes...but not lethal. Or, sometimes the places move...the collection of particles are moving. A cloud of charged particles flows over your neigborhood...and want to connect with the ground. Boom Lightning. Very dangerous and sometimes fatal. Nature. Charged particles. Coming together.

The grounding electrode systems is how your house (and everything in it that is conductive) is electrically connected to the earth. "Bonded" together to provide a relatively smooth and orderly flow of electrical charges. Under most conditions, it's just the normal everyday equalization. Under severe conditions, in the midst atmospheres filled with charged particles, such as a thunderstorm, it shunts charged particles to the earth...keeping both equipment and humans relatively safe. Note that charges during a thunderstorm are everywhere. Lightning that hits miles away can induce current in the line...and all sorts or charges can land on systems in the house.

Now, back to man-made electrons. That's the purpose of that jumper in the SE panel. All the stuff I mentioned in the paras above pretty much ride the EGC to the ground bus, and the GEC to the grounding electrodes...and to the earth. But that power at the transformer...the "low impedance" path is via the neutral. And if a fault occurs to the EGC, then the EGC is the path to the SE, but it needs that connection to the neutral to get back to source. So these man-made source faults need the neutral to trip the OCPD.

Granted, as all paths are taken, some of that man-mad EGC current will run down the GEC to the ground and along the 25 ohm path back to the transformer ground and back to source. But, as others foot stomp over and over....a 25 ohm path isn't enough to create enough current to trip the OCPD.

Back to the original question. Purpose of the grounding electrode system? We live in a universe of charged particles. Keeping those charges relatively constant around us makes for a much more pleasant life, both for us physically as well as the devices we use. And a good connection to ground...and good bonds with that ground...make it so.

Bonding (that eventually gets to ground..earthing) is needed to keep things pleasant in our universe.
Bonding (that eventually gets back to source) is needed to keep us alive when our man-made charged particles get out of the corral.

Key point is the EGC is used for BOTH. It provides the path to ground. And provides the load side path back to source..with the bonding jumper (ground bar to neutral bar) being the key ingredient in that regard.

 

[jaggedben]

Never mind the blimp or hospital OR. lol.

The overall point is I've come across too many electricians, inspectors, and more that don't understand the purpose of the grounding electrode system. Either that or I'm wrong. So let me explain one more time.

The MBJ is responsible for carrying fault current to neutral where it wants to go (source).

The grounding electrodes are mainly for lightning, static, other foreign over voltages and to stabilize the voltage during normal conditions- though I don't understand what we are stabilizing it from.

You keep ignoring 250.4(A)(2). Limiting the voltage between normally non-current-carrying materials and ground. I believe this is about preventing shocks. The primary situation where it would be needed in this country is an open neutral, which is something any seasoned electrician on this forum will have experienced responding to.

The GEC to a water pipe is the lone wolf in that it can potentially become energized by our ungrounded conductors and that's why we size it in proportion to our service. All other connections with our GE's are usually significantly smaller because they are NOT responsible to carry a fault.

As I stated above, we're probably a bit more concerned about something else becoming energized, and developing a potential to the water pipe because both the water and the neutral at the transformer are grounded. If the water pipe doesn't qualify as an electrode we still bond the water pipes so that in case they become energized they serve as a fault path. If the water pipe serves as an electrode then we also use it as a ground.

So we are 5 pages in, and it seems like many on here are endorsing the idea that ground rods have something to do with faults

I don't recall anyone in the thread saying that.

and/or something to do with protection from getting shocked by our system.

I stand by my opinion that this is one of the purposes, particularly when the system isn't operating properly.

What's interesting is it's literally explained in one of the first NEC articles in Grouding: we make a connection to earth for lightning, static...

and to 'limit the voltage to ground.'

I think the confusion comes from the word 'ground fault'. It should be called "non-energized conductive surface fault", we should call our EGC's "equipment bonding conductors" and there should be an explanation for why we size our water pipe GEC according to service size. Grounding should be understood and treated as our connection to earth for foreign overvoltages and bonding should be our connection to all building conductive surfaces to clear faults.

Sometimes it is literally a ground fault. Like when an ungrounded conductor makes contact with a tree, or a buried conductor becomes exposed. As Dave said earth is the ship we are on, and it's hard to keep everything isolated from the ship all the time.

 

[jaggedben]

Here's another example...

Somewhat recently I came upon a subpanel in a detached garage, and there was no EGC from the main house to the subpanel, as is required today (but wasn't when it was installed). But there was also no neutral-to-ground bond at the subpanel. So if there had been a circuit faulting to the panel or any conduit bonded to it, no breaker would have tripped. But at least there was a ground rod. That greatly reduced the chances that, if there had been such a circuit, and I had touched the panel housing, any current wanting to flow would have found a happier path through me than through the ground rod.

 

[al hildenbrand]

The grounding electrodes are mainly for lightning, static, other foreign over voltages and to stabilize the voltage during normal conditions- though I don't understand what we are stabilizing it from.

I'll chime in, along with the other great responses, with this anecdote.

Back in the 1800s, as we started to transmit power over wires run long distances, more than a 1/4 mile, or so, the nature of the Earth to be, simultaneously, an infinite sink, and an infinite source, of electrons (charge) began to show up.

Consider a hypothetical load, a 10 horsepower electric motor water pump, as the only load in a small rural community that was making a community water distribution system. The only electric load in the community is the water tower 10 horsepower pump.

20 miles away, another community has a community electric power plant that agrees to transmit power at 2400 Volts. The first transmission line was a Single Wire, Earth Return line, the engineers, at the time, thinking that the motor is going to draw less than 1/20th of an Amp, and, therefore, at 2400 Volts, the Earth would work just fine as a return conductor. To the engineer's surprise, even with both ends of the transmission line referenced to Earth, they found the pump end measured line-to-Earth voltage to be wildly unpredictable. That is, the voltage at the load was not stable.

Adding a second wire, a transmission line neutral, that also served as a form of lightning protection when mounted above the energized transmission conductor, a neutral that was solidly connected to Earth roughly every three poles, stabilized the pump-end voltage.

I think of the effect of the transmission neutral with many uniformly spaced connections to Earth as a low impedance path that can easily redistribute the differences in the Earth's local electrical charge. It is as if a level trough of electrical charge is created, a level trough on a field of fluctuating highs and lows.

 

[daytonajim00]

Here's another example...

Somewhat recently I came upon a subpanel in a detached garage, and there was no EGC from the main house to the subpanel, as is required today (but wasn't when it was installed). But there was also no neutral-to-ground bond at the subpanel. So if there had been a circuit faulting to the panel or any conduit bonded to it, no breaker would have tripped. But at least there was a ground rod. That greatly reduced the chances that, if there had been such a circuit, and I had touched the panel housing, any current wanting to flow would have found a happier path through me than through the ground rod.

Bingo jaggedben. All separate structures must have grounding electrode per. 250.32. Since it's a subpanel you do NOT bond. You connect your GEC for that seperate structure to the EGC's, add an EGC going back to the house panel and you're done.

If I'm not mistaken, the old code used to let us rebond (neutral-EGC's) in the subpanel at the seperate structure. That's probably why there wasn't an EGC at the garage you visited. Newer codes require the EGC just like any other subpanel. Now the reason we have to set new ground rods on a seperate structure is to offer equal potential between the electrical system at the seperate structure and earth for foreign over voltage, (lightning, static, high voltage utility) - we don't want to leave the GE's at the garage out and rely on the EGC that should be ran back to the main panel for that path.

Once again, the ground rods were not there for clearing a fault. It was an old wiring method you saw that still was out of compliance (with the old code) because it wasn't even bonded.

Hope that came out clear. Shot out to JPinVA for better explaining it.

 

[daytonajim00]

Big shout out to al hildenbrand for explaining the purpose of "stabilizing voltages under normal operation". I was always unsure about the tethering of transformer voltage to earth thing.

 

[jaggedben]

Bingo jaggedben. All separate structures must have grounding electrode per. 250.32. Since it's a subpanel you do NOT bond. You connect your GEC for that seperate structure to the EGC's, add an EGC going back to the house panel and you're done.

If I'm not mistaken, the old code used to let us rebond (neutral-EGC's) in the subpanel at the seperate structure. That's probably why there wasn't an EGC at the garage you visited. Newer codes require the EGC just like any other subpanel. Now the reason we have to set new ground rods on a seperate structure is to offer equal potential between the electrical system at the seperate structure and earth for foreign over voltage, (lightning, static, high voltage utility) - we don't want to leave the GE's at the garage out and rely on the EGC that should be ran back to the main panel for that path.

Once again, the ground rods were not there for clearing a fault. It was an old wiring method you saw that still was out of compliance (with the old code) because it wasn't even bonded.

Hope that came out clear. Shot out to JPinVA for better explaining it.

But once again, like the open service neutral, I could lose the EGC between separate structures. And then the grounding electrode provides a measure of additional safety since your faults aren't being cleared by an OCPD.

I totally agree with JP's post btw. We are all giving you examples of why it's just plain a good idea to ensure that there isn't a voltage potential between the earth and the metal stuff in our buildings. There's lot's of different stuff that could put that there, both man-made and not, both related to the local system and not.

 

[mbrooke]

Food for thought- where the UK previously did not require earth electrodes, they now seem to be mandated in the latest edition:


https://youtu.be/MQGADrQRuhY?t=48s


UK experts will have to chime in- but this could be something to do with the increased use of TN-C-S, but that is just a guess. I'm curious why the IET thought to make this mandate.

 

[Adamjamma]

actually, if you check the 18th edition and check that video, you will find the video came out, like many concerning Arc Fault, before the 18th was released. T-T section has been changed to require extra work to bring it within the regs but no extra ground rods required and the section was finally modified to say we do not need to bond interior metal pipework for water or gas if the entry is plastic... unless the interior pipework is run in such a way as it could be energised.

Extra ground rods or CEE is only required in commercial if it meets certain requirements but TN-s and TN-C-S stayed the same... at least according to SparkChannel and JW...lol... Have not yet recieved my birthday present of the book , but have the onsite guide and the students guide.

 

[ActionDave]

...I think the confusion comes from the word 'ground fault'. It should be called "non-energized conductive surface fault", we should call our EGC's "equipment bonding conductors" and there should be an explanation for why we size our water pipe GEC according to service size. Grounding should be understood and treated as our connection to earth for foreign overvoltages and bonding should be our connection to all building conductive surfaces to clear faults.

This idea that if we change the name from grounding to bonding is a foolish one. The problem is not the wording, the problem is all the romance and superstition that surrounds grounding and lazy people that don't take the time to understand electrical systems.

We have a common vocabulary that works for anybody that cares enough to learn this stuff. If I say Equipment Grounding Conductor you know exactly what I mean.

These are the terms I use

Earth

Grounded - connected to earth

Equipment grounding - connecting all the non current carrying metal parts together

Bond - the one place in the whole system where connect the grounded conductor and equipment grounding conductors together

You go and start calling it bonding and people that screw up grounding are still going screw it up....It will just be a different set of questions-

What do you mean I float the neutral at a sup panel I thought everything needed to be bonded? Do I only bond at the main disconnect or do I bond everything?

 

[kwired]

If I'm not mistaken, the old code used to let us rebond (neutral-EGC's) in the subpanel at the seperate structure. That's probably why there wasn't an EGC at the garage you visited. Newer codes require the EGC just like any other subpanel. Now the reason we have to set new ground rods on a seperate structure is to offer equal potential between the electrical system at the seperate structure and earth for foreign over voltage, (lightning, static, high voltage utility) - we don't want to leave the GE's at the garage out and rely on the EGC that should be ran back to the main panel for that path.

A wrench in the gears... when we were allowed to ground the neutral at a separate structure, we still needed to connect it to a grounding electrode system at that separate structure.

Then (and now we still have) the single branch circuit to a separate structure that doesn't require a grounding electrode. A separate grounded and equipment grounding conductor are required in that branch circuit though.

 

[mbrooke]

actually, if you check the 18th edition and check that video, you will find the video came out, like many concerning Arc Fault, before the 18th was released. T-T section has been changed to require extra work to bring it within the regs but no extra ground rods required and the section was finally modified to say we do not need to bond interior metal pipework for water or gas if the entry is plastic... unless the interior pipework is run in such a way as it could be energised.

Extra ground rods or CEE is only required in commercial if it meets certain requirements but TN-s and TN-C-S stayed the same... at least according to SparkChannel and JW...lol... Have not yet recieved my birthday present of the book , but have the onsite guide and the students guide.

Thank you for clearing this up- I did not know that.