Neutral Conductors and Equipment Grounds tied together a
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Re: Neutral Conductors and Equipment Grounds tied together a
Great thread guys, today i logged in exactly to find out more about bonding grounded to grounding and what i found???? This huge amount of information.
Being an aprentice, i often come here to learn more about the trade, and even tough sometimes things may look somehow confusing, i always end up learning from different experiences
Thanks
Great thread guys, today i logged in exactly to find out more about bonding grounded to grounding and what i found???? This huge amount of information.
Being an aprentice, i often come here to learn more about the trade, and even tough sometimes things may look somehow confusing, i always end up learning from different experiences
Thanks
Re: Neutral Conductors and Equipment Grounds tied together a
X'tian: Ignore my statements. I have been accused of misleading the new people that may be reading this thread. My reading comprehension has also been questioned.
Separate the neutral/ground, and equipment ground conductors in a panel after the service. This is the commonly accepted method, except in detached buildings. You will always be correct with everyone, except me.
I have the same code book as everyone else. I also have many technical, and engineering manuals, and books.
250.24 (5) has nothing to do with a panel after the service. The text is about single point grounding. To phrase it simply; Don't stick the neutral/ground in the dirt after the service.
A panel after the service, if supplied by three circuit conductors, must have the neutral/ground, and equipment/ground conductors bonded in the panel.
When supplied by four conductors, or paths, for current flow, the neutral/ground and equipment/ground conductors must be separated to prevent parallel paths for normal load current.
By installing four wires to a panel, you are increasing the ground fault path impedance. But it is accepted by most people. On a 200 amp feeder you are changing from a 4/0 to a No. #4.
The neutral/ground, with the feeder, of a three wire cable is completing the fault path for the equipment, supplied by the panel. The reference to the neutral not being a ground for equipment after the main, is addressed to branch circuits.
It may not be clearly stated in the code book, and implies the feeder neutral/ground can not be used for grounding purposes, but it is technically incorrect.
Now everyone can question my credibility and intelligence, but show me the math and facts.
X'tian: Ignore my statements. I have been accused of misleading the new people that may be reading this thread. My reading comprehension has also been questioned.
Separate the neutral/ground, and equipment ground conductors in a panel after the service. This is the commonly accepted method, except in detached buildings. You will always be correct with everyone, except me.
I have the same code book as everyone else. I also have many technical, and engineering manuals, and books.
250.24 (5) has nothing to do with a panel after the service. The text is about single point grounding. To phrase it simply; Don't stick the neutral/ground in the dirt after the service.
A panel after the service, if supplied by three circuit conductors, must have the neutral/ground, and equipment/ground conductors bonded in the panel.
When supplied by four conductors, or paths, for current flow, the neutral/ground and equipment/ground conductors must be separated to prevent parallel paths for normal load current.
By installing four wires to a panel, you are increasing the ground fault path impedance. But it is accepted by most people. On a 200 amp feeder you are changing from a 4/0 to a No. #4.
The neutral/ground, with the feeder, of a three wire cable is completing the fault path for the equipment, supplied by the panel. The reference to the neutral not being a ground for equipment after the main, is addressed to branch circuits.
It may not be clearly stated in the code book, and implies the feeder neutral/ground can not be used for grounding purposes, but it is technically incorrect.
Now everyone can question my credibility and intelligence, but show me the math and facts.
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie, that was so clearly stated that I think we can have a rational conversation. You say that if you use a 3-conductor feeder (2 hots and a neutral), you then bond the EGCs to the neutral in the subpanel, and all fault currents go back on the neutral.
My thoughts: first, NEC requires the equipment ground to run with the feeder, i.e., you MUST run four conductor, unless you use the conduit for the EGC. So all other discussion on this is theoretical, since it is a Code violation. But theoretical is fine as long as you don't claim Code compliance.
So my thoughts on the theoretical question are these: granted that a fault will be conducted by the neutral in a three wire feeder, with no problem and perhaps more efficiency. But that's not the problem.
The problem as I have encountered it (I get paid to correct it) is that in normal operation the neutral currents from the branch circuits come to the subpanel where you have the neutral bus accepting both neutrals and EGCs. The neutral current then has the option of returning to the main panel by way of your feeder neutral but also any metallic paths that may be in contact with the subpanel or any equipment grounds using that subpanel. The paths are water pipes, gas pipes, building steel, HVAC ducts, etc etc. So you have set up unplanned parallel paths and caused magnetic fields all over the place, and particularly in the feeder cable.(NEC doesn't like this in part because of the possibility of arcing in hidden places).
So the problem isn't a fault traveling on the neutral, but neutral traveling on multiple paths.
I think all this has been stated many many times, but your post was so clear I thought I would state it one more time, as an experiment.
Karl
Bennie, that was so clearly stated that I think we can have a rational conversation. You say that if you use a 3-conductor feeder (2 hots and a neutral), you then bond the EGCs to the neutral in the subpanel, and all fault currents go back on the neutral.
My thoughts: first, NEC requires the equipment ground to run with the feeder, i.e., you MUST run four conductor, unless you use the conduit for the EGC. So all other discussion on this is theoretical, since it is a Code violation. But theoretical is fine as long as you don't claim Code compliance.
So my thoughts on the theoretical question are these: granted that a fault will be conducted by the neutral in a three wire feeder, with no problem and perhaps more efficiency. But that's not the problem.
The problem as I have encountered it (I get paid to correct it) is that in normal operation the neutral currents from the branch circuits come to the subpanel where you have the neutral bus accepting both neutrals and EGCs. The neutral current then has the option of returning to the main panel by way of your feeder neutral but also any metallic paths that may be in contact with the subpanel or any equipment grounds using that subpanel. The paths are water pipes, gas pipes, building steel, HVAC ducts, etc etc. So you have set up unplanned parallel paths and caused magnetic fields all over the place, and particularly in the feeder cable.(NEC doesn't like this in part because of the possibility of arcing in hidden places).
So the problem isn't a fault traveling on the neutral, but neutral traveling on multiple paths.
I think all this has been stated many many times, but your post was so clear I thought I would state it one more time, as an experiment.
Karl
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Yes, the exception is when the feeder goes to a separate building with NO METALLIC PATHS for the neutral to diverge to.
Karl
Yes, the exception is when the feeder goes to a separate building with NO METALLIC PATHS for the neutral to diverge to.
Karl
G
Guest
Guest
Re: Neutral Conductors and Equipment Grounds tied together a
Again, per NEC but not theoretically required.
Per the NEC the outbuilding would require 4-wire 240-volt circuits, or 3-wire 120-volt circuits too (i.e.- the N-G could not be bonded on say a dryer, receptacle, or switch).
[ September 20, 2003, 07:52 PM: Message edited by: awwt ]
In which case the NEC would require the outbuilding on a 3-wire circuit (assuming a non-conductive conduit or sheathing) to have its own driven ground rod.
Again, per NEC but not theoretically required.
Per the NEC the outbuilding would require 4-wire 240-volt circuits, or 3-wire 120-volt circuits too (i.e.- the N-G could not be bonded on say a dryer, receptacle, or switch).
[ September 20, 2003, 07:52 PM: Message edited by: awwt ]
Re: Neutral Conductors and Equipment Grounds tied together a
The outbuilding panel, with any current path, other than the neutral/ground will require separation of the neutral and equipment ground bus.
Driving a ground rod, on a three wire feeder, will create a parallel load current path through the earth.
A ground rod on a four wire system, with neutral and ground separation, will not provide a parallel path for load current.
The outbuilding panel, with any current path, other than the neutral/ground will require separation of the neutral and equipment ground bus.
Driving a ground rod, on a three wire feeder, will create a parallel load current path through the earth.
A ground rod on a four wire system, with neutral and ground separation, will not provide a parallel path for load current.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
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- ESI, PI, RBO
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie
I disagree.
The earth is a parallel conductor.
Mike P.
Bennie
I disagree.
The earth is a parallel conductor.
Mike P.
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Re: Neutral Conductors and Equipment Grounds tied together a
Mike
When using a 4-wire feeder to a separate building the grounding electrode (ground rod) is connected to the equipment ground buss not the neutral buss. There shouldn't be any load current on the grounding electrode.
Mike
When using a 4-wire feeder to a separate building the grounding electrode (ground rod) is connected to the equipment ground buss not the neutral buss. There shouldn't be any load current on the grounding electrode.
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie, awwt diverted the discussion to ground rods. Back to what we were discussing, your reply indicates to me that you do not dispute my post. Very good. We can discuss and agree.
I think you are a visionary, as seen in your post about the future. That's where your intellect flies. And I agree with the post, especially the umbrella. Busses might be expensive, but plug-ins are the way to go.
(For readers, check out Bennie's post on the Engineering section).
Karl
Bennie, awwt diverted the discussion to ground rods. Back to what we were discussing, your reply indicates to me that you do not dispute my post. Very good. We can discuss and agree.
I think you are a visionary, as seen in your post about the future. That's where your intellect flies. And I agree with the post, especially the umbrella. Busses might be expensive, but plug-ins are the way to go.
(For readers, check out Bennie's post on the Engineering section).
Karl
G
Guest
Guest
Re: Neutral Conductors and Equipment Grounds tied together a
I did not divert the thread to ground rods. Bennie said that a three-wire feeder would be OK or even better. I noted that if you add a ground rod a 3-wire feeder to an outbuilding would be permitted by the NEC.
Bennie countered with: A ground rod would create a parallel load current path.
I am having a valid discussion here too. Please do not belittle or disparage my remarks unless it's really warranted. As a moderator I hold you to a higher standard of conduct than that. I felt that you are asking others to ignore my "diversion". I am not here to divide and conquer. I apologize for not fitting into your mold of how this thread should metamorphose. My ground rod comment is not an unwarranted tangent. It's not a tangent at all. It's integral to the matter at hand.
I take this business very seriously and the consequences are serious. Getting everything out in the open is the best way to find the defects in the thesis. Please don't squash my creative thinking. We all bring something to the table. Many others have a leg up on me. My hope is that no one feels compelled to exert their superior knowledge or power in a belittling fashion.
You are always free to contact me offline too if you have any personal issues with my posting style. I am flexible to change and I am here to learn.
Respectfully,
../Wayne C.
[ September 11, 2003, 11:12 PM: Message edited by: awwt ]
Karl, (paraphrased for brevity):
I did not divert the thread to ground rods. Bennie said that a three-wire feeder would be OK or even better. I noted that if you add a ground rod a 3-wire feeder to an outbuilding would be permitted by the NEC.
Bennie countered with: A ground rod would create a parallel load current path.
I am having a valid discussion here too. Please do not belittle or disparage my remarks unless it's really warranted. As a moderator I hold you to a higher standard of conduct than that. I felt that you are asking others to ignore my "diversion". I am not here to divide and conquer. I apologize for not fitting into your mold of how this thread should metamorphose. My ground rod comment is not an unwarranted tangent. It's not a tangent at all. It's integral to the matter at hand.
I take this business very seriously and the consequences are serious. Getting everything out in the open is the best way to find the defects in the thesis. Please don't squash my creative thinking. We all bring something to the table. Many others have a leg up on me. My hope is that no one feels compelled to exert their superior knowledge or power in a belittling fashion.
You are always free to contact me offline too if you have any personal issues with my posting style. I am flexible to change and I am here to learn.
Respectfully,
../Wayne C.
[ September 11, 2003, 11:12 PM: Message edited by: awwt ]
Re: Neutral Conductors and Equipment Grounds tied together a
Wayne: I have always believed that another ground electrode system on the same premises should not be installed.
I go by section 250.50, specifically if the ground rod in the separate building can not be bonded to the service ground electrode system, then it should not be installed. The panel will be grounded either by the neutral/ground, or the equipment ground conductor of the building ground(service).
Feeding the separate electrodes is not bonding. It is multi point grounding.
Karl's EMF meters will go crazy. :roll:
[ September 11, 2003, 11:29 PM: Message edited by: bennie ]
Wayne: I have always believed that another ground electrode system on the same premises should not be installed.
I go by section 250.50, specifically if the ground rod in the separate building can not be bonded to the service ground electrode system, then it should not be installed. The panel will be grounded either by the neutral/ground, or the equipment ground conductor of the building ground(service).
Feeding the separate electrodes is not bonding. It is multi point grounding.
Karl's EMF meters will go crazy. :roll:
[ September 11, 2003, 11:29 PM: Message edited by: bennie ]
G
Guest
Guest
Re: Neutral Conductors and Equipment Grounds tied together a
Got it! Carry on Captain!
../Wayne C.
Got it! Carry on Captain!
../Wayne C.
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Wayne, you are right, I should not have been annoyed at the introduction of ground rod stuff. You are right to chide me for that.
To get back to the electrical question, I wanted to see if Bennie would agree that subpanels had to have EGCs. I knew I had to mention the exception to keep the discussion on target. The exception of separate buildings does not change the NEC intent of keeping neutral off metallic grounding paths, since 3-wire feeds are not allowed if if there is a metallic path.
The use of a ground rod at the building is irrelevant because the rod/earth impedance is too high to make any difference. Bennie says "Karl's EMF meter will go crazy", but not so. I regularly clamp an ammeter around the GEC to rods just to verify what is happening. It is always too negligible to mention, with the one exception being when the rod was embedded in a salt water stratum at an estuary.
I think I've completed my statements about running an EGC to subpanels, so I will bow out of this thread now.
Karl
Wayne, you are right, I should not have been annoyed at the introduction of ground rod stuff. You are right to chide me for that.
To get back to the electrical question, I wanted to see if Bennie would agree that subpanels had to have EGCs. I knew I had to mention the exception to keep the discussion on target. The exception of separate buildings does not change the NEC intent of keeping neutral off metallic grounding paths, since 3-wire feeds are not allowed if if there is a metallic path.
The use of a ground rod at the building is irrelevant because the rod/earth impedance is too high to make any difference. Bennie says "Karl's EMF meter will go crazy", but not so. I regularly clamp an ammeter around the GEC to rods just to verify what is happening. It is always too negligible to mention, with the one exception being when the rod was embedded in a salt water stratum at an estuary.
I think I've completed my statements about running an EGC to subpanels, so I will bow out of this thread now.
Karl
jcook980
Member
- Location
- Gresham, Oregon
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- Electrical Engineer
Re: Neutral Conductors and Equipment Grounds tied together a
Karl,
Karl,
Where is this stated in the NEC?
- Location
- Illinois
- Occupation
- retired electrician
Re: Neutral Conductors and Equipment Grounds tied together a
jcook,
See 250.32(B)(2).
Don
jcook,
See 250.32(B)(2).
Don
short circuit faulted
Member
- Location
- Columbia SC
Re: Neutral Conductors and Equipment Grounds tied together a
This posting surely was a long and winding road. I would be the first to admit the NEC could surely be written in simple english that many of tables should be organized to fit on on one page, some of the wording simplified, but as I understood the original question. To be when was the requirement to seperate "grounded" from "grounding" conductors at subpanels placed in the code? How did we get to not needing the fourth wire on a subpanel? Best example I can come up with was a service call to an industrial plant regarding ground fault breakers. Plant incoming service 2000A 480/277Y...addition was put on plant with 6 200 amp main lug panels...installed for lighting loads. GFI Breakers feeding panels were tripping. Investigating the problem, found equipment ground and neutral bars in sub panels bonded, causing lost current on grounded conductor and breakers to trip. Remove bonding strap and all is well with the world, and you have a code compliant installation. Have a good day, all!
This posting surely was a long and winding road. I would be the first to admit the NEC could surely be written in simple english that many of tables should be organized to fit on on one page, some of the wording simplified, but as I understood the original question. To be when was the requirement to seperate "grounded" from "grounding" conductors at subpanels placed in the code? How did we get to not needing the fourth wire on a subpanel? Best example I can come up with was a service call to an industrial plant regarding ground fault breakers. Plant incoming service 2000A 480/277Y...addition was put on plant with 6 200 amp main lug panels...installed for lighting loads. GFI Breakers feeding panels were tripping. Investigating the problem, found equipment ground and neutral bars in sub panels bonded, causing lost current on grounded conductor and breakers to trip. Remove bonding strap and all is well with the world, and you have a code compliant installation. Have a good day, all!
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Neutral Conductors and Equipment Grounds tied together a
short circuit faulted:
short circuit faulted:
This would be fine in an industral instalation with the feeders installed in metal conduit, but in a resedental install many use SER cable or other non-metalic type cable/race-ways, a three wire SER cable would not provide a short circuit fault path back to the source if the bonding was removed at the sub-panel. this is why there must be an EGC ran with the feeders.
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Hurk, you say "many" use 3-wire SER cable to subpanels in residential. Who are these "many"? Licensed electricians?
Karl
Hurk, you say "many" use 3-wire SER cable to subpanels in residential. Who are these "many"? Licensed electricians?
Karl
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Neutral Conductors and Equipment Grounds tied together a
Karl
No even though I have run into a few that have but most are done by DYS.
I was just commenting on what he said that it was a simple job to just remove the N/G bond at the sub panel. as we know in a dwelling this is not always the case. as when we run into this type of violation it is in most cases fed by only three conductors and the neutrals and grounds will be terminated on the same busses in the sub panel.
Karl
No even though I have run into a few that have but most are done by DYS.
I was just commenting on what he said that it was a simple job to just remove the N/G bond at the sub panel. as we know in a dwelling this is not always the case. as when we run into this type of violation it is in most cases fed by only three conductors and the neutrals and grounds will be terminated on the same busses in the sub panel.
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