Electrical Grounding
#1
07-06-04, 01:51 AM
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:
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
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
#2
07-06-04, 04:16 AM
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.?
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.
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.
#3
07-06-04, 06:59 AM
Member
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.
GEC: ... Also known as the Grounding Conductor.
Now, if a GFCI is present, then the EGC should never be used
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.
What protects against a ground fault? The neutral, right?
#4
07-06-04, 10:30 AM
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.
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
07-06-04, 10:41 AM
From the 2002 NEC
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.
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.
#6
07-06-04, 11:26 AM
Originally Posted by Vector
No, the neutral or "grounded conductor" does not protect against a ground fault.
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.
Originally Posted by Vector
If these chassis were tied to neutral they would always be energized, and a shock hazard.
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).
Thanks for the replies. I'll keep trying to understand this
#7
07-06-04, 11:46 AM
Member
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
07-06-04, 05:44 PM
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.
#9
07-06-04, 08:05 PM
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
#10
07-06-04, 09:02 PM
Member
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
07-07-04, 12:29 AM
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.
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 Neutral
" These are accidental connections. Direct-short faults cause the largest fault current to flow".
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.
"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
07-07-04, 02:45 PM
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
07-07-04, 10:47 PM
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
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
