"Grounding Electrode Conductor" vs. "Equipment Grounding Conductor"

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tankfarms

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"Grounding Electrode Conductor" vs. "Equipment Grounding Conductor"

This is one of those things that I thought I knew and then I read more from the NEC and then I get a bit more confused. So my questions are (based on the 2011 NEC)

1. What's the difference b/t "Grounding Electrode Conductor" vs. "Equipment Grounding Conductor"
2. Can someone elaborate a bit more on article 250.121?

Thanks.
 
The GEC- is used to bond the grounding electrode system together. Thus the water pipes, steel, ground rods, etc get connected to the GEC.

The egc is the wire in cable or conduit which grounds the equipment being served.
 
I will add that the GEC is all about connecting the electrical system to planet Earth, that is to say, connecting it to dirt. There are many good reasons for doing this, and many of them are open to debate. So I won't go into that discussion here.


The EGC is all about tripping the breaker (or blowing the fuse) on a fault situation, so as to prevent damage to equipment or to human bodies. Inside a metal tool, for example, the EGC would be attached to the tool's external metal case on one end, and (ultimately) to the N-G bond point in the main panel on the other end. If there is a short circuit inside the tool, such that the metal case becomes energized, then the EGC would carry a large fault current back to the source. Since that current flows from the panel via a circuit breaker (or fuse), it will cause the breaker to trip (or fuse to open), and that will stop the flow of current and thereby terminate the event.
 
tankfarms said:
2. Can someone elaborate a bit more on article 250.121?
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Continuing from my previous discussion, if you connect the EGC to the tool's metal case on one end, and to planet Earth on the other end (i.e., instead of to the N-G bond point, where it belongs), then the path for fault current returning to the source could include some amount of dirt. The resistance of a planet's worth of dirt is low enough by itself, but the resistance of the interface between dirt and ground rods is not so low. Thus, the total resistance of the fault path could be high enough to cause the amount of fault current to be too low to trip the breaker. That would essentially prevent the EGC from being able to do its job.
 
tankfarms said:
This is one of those things that I thought I knew and then I read more from the NEC and then I get a bit more confused. So my questions are (based on the 2011 NEC)

1. What's the difference b/t "Grounding Electrode Conductor" vs. "Equipment Grounding Conductor"
2. Can someone elaborate a bit more on article 250.121?

Thanks.
Click to expand...

Have you looked at the definitions provided in Article 100?

Grounding Conductor, Equipment (EGC). The conductive
path installed to connect normally non?currentcarrying
metal parts of equipment together and to the system
grounded conductor or to the grounding electrode
conductor, or both.
Click to expand...


Grounding Electrode Conductor. A conductor used to
connect the system grounded conductor or the equipment to
a grounding electrode or to a point on the grounding electrode
system.
Click to expand...

250.121?
 
charlie b said:
New in the 2011. "An equipment grounding conductor shall not be used as a grounding electrode conductor."
Click to expand...

Thanks, I don't know why I did not see that the first time. :ashamed1:

250.121 Use of Equipment Grounding Conductors. An
equipment grounding conductor shall not be used as a
grounding electrode conductor.
Click to expand...

Back to the OP.

Say you ran a feeder from a house to a detached garage, the feeder would have two hots and neutral and an EGC.

At the detached garage 250.32(A) requires a grounding electrode system. It would be tempting to use the EGC as a GEC in order to use the grounding electrode system back at the main house.

Up until the 2011 it was unclear if that would be acceptable or not, now with the addition of 250.121 it is clearly not allowed.

I think one of our forum members may have been the one whose code proposal resulted in this change.
 
iwire said:
Thanks, I don't know why I did not see that the first time. :ashamed1:



Back to the OP.

Say you ran a feeder from a house to a detached garage, the feeder would have two hots and neutral and an EGC.

At the detached garage 250.32(A) requires a grounding electrode system. It would be tempting to use the EGC as a GEC in order to use the grounding electrode system back at the main house.

Up until the 2011 it was unclear if that would be acceptable or not, now with the addition of 250.121 it is clearly not allowed.

I think one of our forum members may have been the one whose code proposal resulted in this change.
Click to expand...
So, if you didn't have a ground rod at the garage and you ran a ground wire from a subpanel in the garage and bonded it to the grounding system for the house, that would make that wire an EGC used as a GEC and therefore a violation? If you drove a ground rod at the garage and bonded it to the origination point of the aforementioned wire that would correct it?
 
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ggunn said:
So, if you didn't have a ground rod at the garage and you ran an EGC from the garage and bonded it to the grounding system for the house, that would make that wire an EGC used as a GEC and therefore a violation?
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That is my understanding of it.

If you really tried to do it you would have to start with the GEC unspliced from the detached garage all the way back to the grounding electrode. And then call that the EGC as well.
 
While this has been muddy waters for a while, if we look at 250.50 the words
at each building or structure served
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kind of seem to mean it is intended to only use electrodes at each building or structure served? this has come up at a few IAEI meetings, and this was the answer that was given, so to me this means running an GEC back to another building or structure would not meet this section?
 
charlie b said:
New in the 2011. "An equipment grounding conductor shall not be used as a grounding electrode conductor."
Click to expand...

The question is, can a grounding electrode conductor be used as an equipment grounding conductor?

Also, for anyone who would like to further confuse themselves ... take a look at 690.47(C). :p
 
hurk27 said:
While this has been muddy waters for a while, if we look at 250.50 the words kind of seem to mean it is intended to only use electrodes at each building or structure served? this has come up at a few IAEI meetings, and this was the answer that was given, so to me this means running an GEC back to another building or structure would not meet this section?
Click to expand...

What is 'at'?
 
hurk27 said:
... so to me this means running an GEC back to another building or structure would not meet this section?
Click to expand...
You mean grounding the neutral at a detached building is a violation?
 
iwire said:
What is 'at'?
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Here it is but that could be argued also.

250.50 Grounding Electrode System.
All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.
Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete.
Click to expand...
 
It has to do with the resistance of individual 'grounds'.If high and nearby bond together.If low and far apart,dispense with bonding.Just a thought.
 
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