The History the Name Equipment Grounding Conductor

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JPinVA

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Does anyone know the historical traccability of the the name EGC, as well as its definition, as it has evolved in the NEC over the years.

I ask this question because at the state we are today, the 2017 code, we have a name of a conductor that does not reflect its primary purpose. The primary purpose (by NEC definition) of the EGC is not the grounding (grounded) state of the EGC, but its role in clearing a fault. It's role is a low impedance path back to source. That path is not ground. In fact, it cannot be ground per NEC. The path is via the neutral. It's the connection to the neutral, not to ground, that establishes the low impedance path that clears the fault.

I ask also because Mike foot stomps the problems the industry has regarding the misunderstanding of the ground's role in clearing a fault. Yet, here we are in 2017 code, with the name of the conductor used to clear a fault being described using the very word (grounding) that cause the misunderstanding of its role.

Is the EGC term a carry over from the days when "grounding" was the thinking of the era, with the definition changing to reflect our better understanding of its role? Or is it something different. I would be interested in the history of the term and how we got where we are today. And, if anyone knows, where we might be headed in the future.
 
180920-0902 EDT

AM
JPinVA:

I have no idea of the history, but 3 prong plugs appeared in the early 1950s.

I believe the purpose was to make exposed conductive surfaces at or near ground (earth) potential to protect people from getting shocked. This would mean that leakage currents would not raise said conductive surface voltage much above earth potential, and thus the difference in potential between surrounding objects that are generally at earth potential, as an example water pipes, would be small. Note below that this protection is a relative matter. High voltages can occur under dead short circuit conditions.

Even with EGCs connected to earth and to exposed conductive surfaces you can get a high voltage between earthed things and the conductive surface when there is a low impedance short from a hot line to the conductive surface.

With a #12 hot and #12 EGC and a short between hot and EGC you will get about 1/2 the source voltage of hot at the point of shorting relative to earth. Based on the EGC being connected to neutral and earth at the main panel.

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180920-0950 EDT

To simplify my previous statement.

The reason EGC is named Equipment Grounding Conductor is that its purpose is to ground (earth) exposed conductive surfaces.

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MIke Holt has been a vocal proponent of changing the name from EGC to EBC (equipment bonding conductor) which is IMO the correct term.
 
180920-1015 EDT

infinity:

I believe the original purpose of the EGC was to reduce shock hazards. In particular from leakage currents. Thus, the name is appropriate.

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gar said:
180920-1015 EDT

infinity:

I believe the original purpose of the EGC was to reduce shock hazards. In particular from leakage currents. Thus, the name is appropriate.

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Click to expand...

That may be true but it no longer holds water when we apply the current NEC defintions. Once we go past the MBJ in the service the objective is to provide a low impedance path for the fault current back to the neutral through the MBJ not to the earth which is the NEC definiton of "grounding". After the MBJ we "bond" everything together.
 
gar said:
180920-1015 EDT

infinity:

I believe the original purpose of the EGC was to reduce shock hazards. In particular from leakage currents. Thus, the name is appropriate.

.
Click to expand...

Leakage currents today are very small, much less than decades past. In most appliances you can unhook the EGC, stand on a grounded surface, touch the frame, and not feel anything. Not that you should try it though.
 
infinity said:
MIke Holt has been a vocal proponent of changing the name from EGC to EBC (equipment bonding conductor) which is IMO the correct term.
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Yes, EBC would make it much better. And it would be just a one letter change on the acronym. Not to mention avoiding the typo/dyslexia problem between the EGC and GEC. And the problem with typing "grounded" for the EGC instead of "grounding" thereby raising confusion with the grounded conductor (i.e., neutral). And, of course, the fact all three...EGC, GEC, and Grounded Conductor...are all connected. EBC would help these issues in multiple ways.
 
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I don't find it that big of a deal. 100 yrs. why change now; call one Vern and the other Willy.
 
About a year ago, I had a disagreement with Mike on this topic. He convinced me I was wrong. What I am about to type is not the way Mike explained it to me, but rather my own take on the subject (after having agreed with Mike). So here is one way you can look at it, if you are willing:
  1. The primary purpose of the EGC is, in fact, to connect the motor's case to planet Earth. That way, there will be no difference in potential between your hand, as you touch the case, and your feet, which are standing on the Earth.
  2. A side benefit (and it is a very important one!) is that the EGC allows a high fault current to flow in the event of a fault, which causes the OCPD to open the fault path, thereby terminating the event.

I had originally argued that item 2 was the only EGC function. But now I see that we are indeed connecting metal stuff to dirt.
 
charlie b said:
A
  1. The primary purpose of the EGC is, in fact, to connect the motor's case to planet Earth. That way, there will be no difference in potential between your hand, as you touch the case, and your feet, which are standing on the Earth.
  2. A side benefit (and it is a very important one!) is that the EGC allows a high fault current to flow in the event of a fault, which causes the OCPD to open the fault path, thereby terminating the event.

Click to expand...



Regarding #1, more of an explanation is needed on how or why that is. I have a theory...
 
mbrooke said:
Regarding #1, more of an explanation is needed on how or why that is. I have a theory...
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It has to do with normal operations, not fault conditions. Current (think "motor windings") creates magnetic fields in the surrounding air, which in turn can induce current in nearby metal objects (think "motor case"). That in turn means that the metal objects can have a potential difference with respect to "ground" (meaning "dirt"). If you touch such a metal object while standing on dirt (or a concrete floor, which has dirt below it), that potential difference will cause current to flow through your body. The amount of current is most likely to be insignificantly small, but it will not be zero. In order to make sure it is zero, you connect a wire to the metal case and stick the other end into dirt. Well, actually, you connect a green wire to the case, run it back to the ground bar in the main panel, which is connected to the neutral bar, and there is another wire (the GEC) running from there to the grounding electrode system (i.e., to "dirt"). Thus, without regard to the presence of magnetic fields with and surrounding the motor, the potential difference between the motor case and the dirt will be zero.

 
charlie b said:
It has to do with normal operations, not fault conditions. Current (think "motor windings") creates magnetic fields in the surrounding air, which in turn can induce current in nearby metal objects (think "motor case"). That in turn means that the metal objects can have a potential difference with respect to "ground" (meaning "dirt").
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I disagree, magnetic fields will simply create circulating currents in what ever metal is nearby. This will not involve earth- think of the squirrel cage rotor inside an induction motor, there are heavy currents within it. Yet if I was to use plastic bearings, it would not shock me.




If you touch such a metal object while standing on dirt (or a concrete floor, which has dirt below it), that potential difference will cause current to flow through your body. The amount of current is most likely to be insignificantly small, but it will not be zero. In order to make sure it is zero, you connect a wire to the metal case and stick the other end into dirt. Well, actually, you connect a green wire to the case, run it back to the ground bar in the main panel, which is connected to the neutral bar, and there is another wire (the GEC) running from there to the grounding electrode system (i.e., to "dirt"). Thus, without regard to the presence of magnetic fields with and surrounding the motor, the potential difference between the motor case and the dirt will be zero.
Click to expand...

Assuming a leakage of 5ma through a resistor or capacitance coupling in an appliance, most leakage current will return through the service neutral.
 
mbrooke said:
I disagree, magnetic fields will simply create circulating currents in what ever metal is nearby. This will not involve earth- . . .
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Yes, with respect to the "nearby" eddy currents, however that is not the sole result of the generator principle.

The induced current will take ALL available paths. If this were not true, we would not be able to deliver power-at-a-distance, rather all a generator would do is create eddy currents in its "nearby" windings.

When the "circuit" floats we have the special case of an ungrounded system. In an ungrounded system, with current flowing in the circuit, when a "ground fault" occurs, voltage relative to ground will occur along the circuit as determined by V = I x R.
 
al hildenbrand said:
Yes, with respect to the "nearby" eddy currents, however that is not the sole result of the generator principle.

The induced current will take ALL available paths. If this were not true, we would not be able to deliver power-at-a-distance, rather all a generator would do is create eddy currents in its "nearby" windings.

When the "circuit" floats we have the special case of an ungrounded system. In an ungrounded system, with current flowing in the circuit, when a "ground fault" occurs, voltage relative to ground will occur along the circuit as determined by V = I x R.
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And in such a case, the minute voltage gradient across the surface of the motor from induced current remains floating. A person touching it odes not complete the circuit, but if you attach an ECG, now one side is earthed the other side of the frame through the person. You have a loop.


However, if you are talking about capacitive coupling, especially on a single phase motor ( I'd imagine a 3 phase motor is like a 3 phase wye cap bank with minimal neutral voltage to ground) then yes do have a frame that is technically above earth potential at a measurable point.
 
mbrooke said:
And in such a case, the minute voltage gradient across the surface of the motor from induced current remains floating.
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You're missing the point, IMO. This is about the Equipment Grounding Conductor (EGC) which is installed as a mesh, a web, a net-like set of multiple low impedance connections that includes reference directly to Earth. The point comes when there is an absence of any low impedance EGC connection to Earth.

While you may have a single motor connected to Earth only by a single wire-type EGC, you cannot rule out a current loop through interconnected conductive items, all of which floats, permitting a portion of an eddy current to leave the "un-Earthed" motor body at one point and return at another. NOW, introduce a ground fault at a distant-from-the-motor chassis point, and go measure the voltage from the chassis to Earth. . . can you guarantee that resultant voltage will never be physiologically significant?
 
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