Electrical Grounding

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  #1  
Old 07-06-04, 01:51 AM
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doingitmyself
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Electrical Grounding

I just can't seem to get this in my head.

First, some indication as to where I am right now in my understanding - it involves the following electrical terms:
  • EGC: That conductor which runs from an appliance to the main panel grounding bus.
  • GEC: That conductor which runs from the main panel to the ground rod. This is usually a #4 bare wire; Also known as the Grounding Conductor
  • Grounded Conductor: The white neutral which goes back to the transformer.
  • Gounding Conductor: The bare wire in the panel which runs to the ground rod. Same as GEC, above.
  • Gounding Electrode: The Ground Rod, to which all bare and green wires in the panel are connected.

It has been said: The purpose of the Grounding conductors, and the ground rod are not to provide protection from fault current. It's purpose is for lightening and surges.

My Question: What's so special, then, (if not for the protection from a ground fault, and beyond the purpose of a GFCI, which can be used with or without a grounded system), for kitchen appliance ground requirements? Surely, this serves no particular protection for the kitchen area, unless, of course, lightening picks on kitchen circuits particularly often.

So much is being said of the importance of a grounded system. That importance being said to protect against lightening. What protects against a ground fault? The neutral, right? So what's the need for all the EGC, GEC, etc. etc. etc.?

I've seen John N's frequent disclaimers that (paraphrased) the EGC's, and the GEC's, and etc. has nothing at all to do with connections to dirt and earth. Yet, they are all connected either directly or indrectly to the dirt.

-Terry
 
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  #2  
Old 07-06-04, 04:16 AM
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Originally Posted by doingitmyself
So much is being said of the importance of a grounded system. That importance being said to protect against lightening. What protects against a ground fault? The neutral, right? So what's the need for all the EGC, GEC, etc. etc. etc.?
No, the neutral or "grounded conductor" does not protect against a ground fault.

During the normal use of a circuit, the neutral conductor carries current.
During the normal use of a circuit, the EGC does not carry current.

In the case of a "ground fault" the EGC carries current to prevent the chassis and other metal parts of grounded (3-prong plug) appliances from becoming dangerously energized. If these chassis were tied to neutral they would always be energized, and a shock hazard.

Now, if a GFCI is present, then the EGC should never be used, as the GFCI will disconnect the circuit. But how many dishwashers, disposals, gas ranges, vent hoods, etc have GFCI? Remember, GFCI protection is only required for countertop outlets.

The grounding system for a kitchen is no different from anywhere else in the house, except that is is probably (next to the bathroom) the most likely place for the combination of high-current device usage, and potential wiring faults (water, sticking a fork in the toaster, etc). That's why additional attention is paid to this area (and why GFCIs are required).

Originally Posted by doingitmyself
I've seen John N's frequent disclaimers that (paraphrased) the EGC's, and the GEC's, and etc. has nothing at all to do with connections to dirt and earth. Yet, they are all connected either directly or indrectly to the dirt.
They are connected to dirt, but most importantly, they are connected to the neutral circuit from the transformer. That is, barring a failure of the neutral service conductor, where 99+% of the current carried by the "grounding" system will go.

The additional grounding provided by grounding rods and bonding to water services works to provide an additional path for the current in the case where the neutral is compromised, or, for whatever reason (electrical storms) the incoming neutral is energized above the normal "ground" potential.
 
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Old 07-06-04, 06:59 AM
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I've seen John N's frequent disclaimers that (paraphrased) the EGC's, and the GEC's, and etc. has nothing at all to do with connections to dirt and earth. Yet, they are all connected either directly or indrectly to the dirt.
That's not what I said. Clearly the GEC has everything to do with connections to dirt. It's the EGC that doesn't need a connection to dirt to do its main job.

GEC: ... Also known as the Grounding Conductor.
I don't have my NEC with me, but I'm guessing that the GEC is not also known as the "grounding conductor".

Now, if a GFCI is present, then the EGC should never be used
I understand what you meant, but this could be misinterpreted so I'll add a clarifying note. If you install a GFCI on a circuit with a grounding conductor, you should certainly connect that grounding conductor to the green screw on the GFCI. If the hot wire were to contact the chassis of the appliance, we want the breaker to trip immediately--not wait until somebody touches that chassis which will bring the GFCI into play. No sense taking that kind of a chance.

What's so special, then, (if not for the protection from a ground fault, and beyond the purpose of a GFCI, which can be used with or without a grounded system), for kitchen appliance ground requirements? Surely, this serves no particular protection for the kitchen area, unless, of course, lightening picks on kitchen circuits particularly often.
The kitchen has no specific grounding requirements. The kitchen's grounding requirements are the same as the rest of the house. And as already indicated, the EGC has nothing to do with lightening protection.

What protects against a ground fault? The neutral, right?
As vector already said, the neutral play no role in protecting against a ground fault, except in the case of a GFCI where it provides a comparison current for the GFCI electronics.
 
  #4  
Old 07-06-04, 10:30 AM
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Originally Posted by John Nelson
I understand what you meant, but this could be misinterpreted so I'll add a clarifying note. If you install a GFCI on a circuit with a grounding conductor, you should certainly connect that grounding conductor to the green screw on the GFCI. If the hot wire were to contact the chassis of the appliance, we want the breaker to trip immediately--not wait until somebody touches that chassis which will bring the GFCI into play. No sense taking that kind of a chance.
I did phrase that badly. What I should have said was:

If a GFCI is present, then the EGC should never carry current, as the GFCI will disconnect the circuit.

Of course the EGC should still be connected to the receptacle.
 
  #5  
Old 07-06-04, 10:41 AM
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From the 2002 NEC

Grounding Conductor. A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.
Grounding Electrode Conductor. The conductor used to connect the grounding electrode(s) to the equipment grounding conductor, the the grounded conductor, or to both, at the service, at each building or structure where supplied from a common service, or at the source of a separately derived system.
These sound similar, but I believe that the Grounding Electrode Conductor is a specific instance whereas Grounding Conductor is a general reference. That is to say that all G-E-Cs are Grounding Conductors, but not all Grounding Conductors are G-E-Cs.
 
  #6  
Old 07-06-04, 11:26 AM
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doingitmyself
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Originally Posted by Vector
No, the neutral or "grounded conductor" does not protect against a ground fault.
I didn't mean to say that the neutral "protected" against a ground fault. I mant to say that, in the case of a fault, the current would use the neutral, and not the GES as the path of least resistance back to the source, and would, therefore trip the CB. Having fault current travel long distances and through different soil conditions of the earth back to the source would provide more resistance, would it not?

Originally Posted by Vector
In the case of a "ground fault" the EGC carries current to prevent the chassis and other metal parts of grounded (3-prong plug) appliances from becoming dangerously energized.
It would carry the current back to the panel to the point where the EGC and the neutral are bonded. It would then use the neutral, as the path of least resistance, back to the transformer, through the transformer windings, back to the circuit breaker on the hot wire and trip the breaker.

Originally Posted by Vector
If these chassis were tied to neutral they would always be energized, and a shock hazard.
I think I can see that, with the exception of three-wire Dryer and Stove circuits, the neutral is not bonded to the chassis.

Originally Posted by Vector
The grounding system for a kitchen is no different from anywhere else in the house, except that is is probably (next to the bathroom) the most likely place for the combination of high-current device usage, and potential wiring faults (water, sticking a fork in the toaster, etc). That's why additional attention is paid to this area (and why GFCIs are required).
A very interesting fact about the toaster: It is absolutely not allowed to be grounded due to the shock factor of having a path between the knife and grounded chassis of the toaster.

Thanks for the replies. I'll keep trying to understand this
 
  #7  
Old 07-06-04, 11:46 AM
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It is not useful to refer to an unnamed "fault" as if all faults were the same. There are many different kinds of faults, and different safety mechanisms come into play for different kinds of faults.
 
  #8  
Old 07-06-04, 05:44 PM
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doingitmyself
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Originally Posted by John Nelson
It is not useful to refer to an unnamed "fault" as if all faults were the same. There are many different kinds of faults, and different safety mechanisms come into play for different kinds of faults.
Ground Faults: Phase conductor contacts metal casing of an appliance. Or Phase conductor contacts grounding wire.
 
  #9  
Old 07-06-04, 08:05 PM
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Rlfrazee
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Just thought I'd throw my 2 cents worth in the heap. Very controversial subject as we know. First I believe the distinction between the grounding conductor and the GEC (grounding electrode conductor) is the use of seperately derived systems such as generators where no ground exists at the equipment. Second I believe the EGC will indeed carry current with a gfci present. Meaning a direct short from the ungrounded conductor to the EGC or the grounded conductor (neutral) will carry such a massive inrush of current that the breaker will trip but not the GFCI. Many times the GFCI will be destroyed or severly damaged if this occurs. The toridal coils of the GFCI will burn up from this interrupting current or will be damaged to the point the GFCI will reset but will not monitor current leakage as is designed. Many times the contacts inside the gfci will weld making the gfci hot even though it is tripped. Well this is a little off subject but just my thoughts......RL
 
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Old 07-06-04, 09:02 PM
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That's an interesting definition, doingitmyself. But where'd you get it from?? There are certainly types of ground faults which don't fit either of those definitions (such as what happens when you throw a toaster into the bathtub), so it doesn't sound like a very good definition to me.
 
  #11  
Old 07-07-04, 12:29 AM
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doingitmyself
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Originally Posted by John Nelson
That's an interesting definition, doingitmyself. But where'd you get it from?? There are certainly types of ground faults which don't fit either of those definitions (such as what happens when you throw a toaster into the bathtub), so it doesn't sound like a very good definition to me.
I believe that the whole context of my post was aimed toward ground faults. The fact that I omited the prefix "ground" in some references shouldn't have implied that I was talking of all faults.

Two general types of faults that I've learned: (from Electrical Grounding 4th Edition, Ronald P. O'Riley - he has an updated 8th editon out also. I recommend it to everyone; very nicely priced!)

"Faults are generally divided into two types- direct shorts and ground fault."
Attention drawn to Section 110-10 of the 1996 NEC (yes, I know it's old).

    Phase to Phase (line to line, hot wire to hot wire)
    Phase to Neutral

    " These are accidental connections. Direct-short faults cause the largest fault current to flow".
      Phase to Ground
      Phase to Equipment

      "Ground faults occur when a phase conductor is connected to ground... an accidental connection between a phase conductor and any grounded surface, such as a grounded metal enclosure... will cause about 75% as much fault current to flow as a direct short." "When a ground fault takes place, the equipment grounding conductor serves a very important function. it furnishes a low impedance path for fault current to reach and cause the circuit overcurrent protective device to operate, thereby limiting the time the fault exists".

      Originally Posted by John Nelson
      Clearing a fault is not the purpose of the GEC.
      I'm still "Repeating the following as often as necessary:"

      "The GEC is useless for a fault situation."
      "The GEC is useless for a fault situation."
      "The GEC is useless for a fault situation."
      "The GEC is useless for a fault situation."
      "........."
      The toaster in the bathtub thing? I'm here to learn

      Thanks for the time,
      Terry
       

      Last edited by doingitmyself; 07-07-04 at 01:04 AM.
        #12  
      Old 07-07-04, 02:45 PM
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      Rlfrazee
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      Was wondering your interpretation of accidental connection in your definitions above. Was the author refering to a mistake during wiring or a field accident e.g. fork from hilo severing conduit run creating direct short between phase conductors? Just curious not questioning the accuracy of the author..... rl
       
        #13  
      Old 07-07-04, 10:47 PM
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      doingitmyself
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      rl,

      I believe the author is referring to the "field accident" you refer to, or an overcurrent situation. He goes on, in the same section, to deferentiate between "an Overload (which) occurs when electrical equipment or a conductor is operated in excess of its rated current" and an "Overcurrent (which) is an excessive current cause by a short circuit or a ground fault. Electrical faults current conditions". These definitions are from NEC 100, Definitions.

      Another part of the NEC states that equipment grounding bonding jumpers shall be large enough to conduct the fault current they may be exposed to.

      tw
       
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