Neutral Conductors and Equipment Grounds tied together a
- Thread starter shanz
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russ
Senior Member
- Location
- Burbank IL
Re: Neutral Conductors and Equipment Grounds tied together a
250.6 Objectionable Current over Grounding Conductors.
I can't remember it being any different than it is now.
I've been in the trade for more than 30 years, but I don't have the resources to look up something like this.
Somebody here probably can add a lot more to this.
Russ
250.6 Objectionable Current over Grounding Conductors.
I can't remember it being any different than it is now.
I've been in the trade for more than 30 years, but I don't have the resources to look up something like this.
Somebody here probably can add a lot more to this.
Russ
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
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- ESI, PI, RBO
Re: Neutral Conductors and Equipment Grounds tied together a
Karl
Didn't you have a reference to this going back to the 30's? I thought I had it book mark.
Mike P.
Karl
Didn't you have a reference to this going back to the 30's? I thought I had it book mark.
Mike P.
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Actually, the article governing this prohibition is (2002) "250.24(5)Load-Side Grounding Connections. A grounding connection may not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article."
I don't know when this first went into the NEC, but suspect it was many decades ago. Perhaps Bennie has this data, or someone else. I have never heard anyone claim that a particular subpanel with a bonded neutral bus was grandfathered.
Karl
Actually, the article governing this prohibition is (2002) "250.24(5)Load-Side Grounding Connections. A grounding connection may not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article."
I don't know when this first went into the NEC, but suspect it was many decades ago. Perhaps Bennie has this data, or someone else. I have never heard anyone claim that a particular subpanel with a bonded neutral bus was grandfathered.
Karl
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
In the article I quoted. Is there a problem with the wording?
In the article I quoted. Is there a problem with the wording?
G
Guest
Guest
Re: Neutral Conductors and Equipment Grounds tied together a
Sounds like more nomenclature confusion. When the rules get voluminous it's difficult to use consistent and proper nomenclature when describing things with words.
../Wayne
PS: Hey, I just noticed a Speall Check button at the bottom of the REPLY text box! WooHoo! Or, have I had my head in the sand again?
[ September 07, 2003, 05:22 PM: Message edited by: awwt ]
Sounds like more nomenclature confusion. When the rules get voluminous it's difficult to use consistent and proper nomenclature when describing things with words.
../Wayne
PS: Hey, I just noticed a Speall Check button at the bottom of the REPLY text box! WooHoo! Or, have I had my head in the sand again?
[ September 07, 2003, 05:22 PM: Message edited by: awwt ]
Re: Neutral Conductors and Equipment Grounds tied together a
The confusion is from the use of "ed" and "ing" in the text.
There has never been a requirement that the neutral/ground and equipment ground bus be isolated in a panel.
The only requirement is to prevent parallel load current flow. Adding the fourth wire created a parallel path. The cure was to separate the neutral/ground from the enclosure.
A cable assembly can be 3 wires and there will not be a parallel path. A metal conduit, will require the neutral to float.
There was no need to add the fourth wire, other than to market more wire.
The confusion is from the use of "ed" and "ing" in the text.
There has never been a requirement that the neutral/ground and equipment ground bus be isolated in a panel.
The only requirement is to prevent parallel load current flow. Adding the fourth wire created a parallel path. The cure was to separate the neutral/ground from the enclosure.
A cable assembly can be 3 wires and there will not be a parallel path. A metal conduit, will require the neutral to float.
There was no need to add the fourth wire, other than to market more wire.
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie
What about this.
Panel A we will call it the main.
Panel B we will call it the sub.
Panel A feeds one branch circuit in a four gang box. The box is not metal.
Panel B feeds another branch circuit in this same box.
Grounded conductors are seperate as required.
All egc are connected as required.
In your 3 wire setup and my example Panel B "neutral" current could return via the egc's. Parallel path?
Am I correct or am I not understanding your point?
Mike P.
Bennie
What about this.
Panel A we will call it the main.
Panel B we will call it the sub.
Panel A feeds one branch circuit in a four gang box. The box is not metal.
Panel B feeds another branch circuit in this same box.
Grounded conductors are seperate as required.
All egc are connected as required.
In your 3 wire setup and my example Panel B "neutral" current could return via the egc's. Parallel path?
Am I correct or am I not understanding your point?
Mike P.
Ed MacLaren
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Objectionable current is any current other than the temporary currents which are set up under fault conditions while the grounding conductors are performing their intended protective functions.
There shouldn't be any need for another rule.
I'm sure you must remember the days before equipment grounding conductors, when ground faults in equipment didn't often trip breakers or blow fuses. I remember a lot of "live" washer and dryer enclosures.
The fact is, in terms of safety, the Equipment Grounding Conductors (ECGs) are much more important than the Grounding Electrode Conductor (GEC) in an installation.
Ed
[ September 07, 2003, 08:36 PM: Message edited by: Ed MacLaren ]
There are already rules specifying the measures to be taken to ensure that objectionable (load) current does not flow in grounding (includes equipment grounding) conductors.
Objectionable current is any current other than the temporary currents which are set up under fault conditions while the grounding conductors are performing their intended protective functions.
There shouldn't be any need for another rule.
Bennie, I am surprised that you would make such a statement. There are many folks here that might actually think that it is accurate.
I'm sure you must remember the days before equipment grounding conductors, when ground faults in equipment didn't often trip breakers or blow fuses. I remember a lot of "live" washer and dryer enclosures.
The fact is, in terms of safety, the Equipment Grounding Conductors (ECGs) are much more important than the Grounding Electrode Conductor (GEC) in an installation.
Ed
[ September 07, 2003, 08:36 PM: Message edited by: Ed MacLaren ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Neutral Conductors and Equipment Grounds tied together a
I think that one thing that is not understood is that when we run just three conductors L1,L2,N to a sub panel we forget that the voltage drop on the neutral will be imposed on the grounding of this sub-panel and because of grounding in a dwelling the water pipes and other things will be at the main service potential this will give you a voltage between these two grounds and or cause multiple grounding if accidental contact comes into play. which in-turn will parallel the sub-panel neutral with most likely a grounding conductor that will only be a #12,14 AWG.
I think this was why we are still allowed to run three conductor to a remote out building when no other grounded path's exist.IE. a water pipe
[ September 07, 2003, 08:49 PM: Message edited by: hurk27 ]
I think that one thing that is not understood is that when we run just three conductors L1,L2,N to a sub panel we forget that the voltage drop on the neutral will be imposed on the grounding of this sub-panel and because of grounding in a dwelling the water pipes and other things will be at the main service potential this will give you a voltage between these two grounds and or cause multiple grounding if accidental contact comes into play. which in-turn will parallel the sub-panel neutral with most likely a grounding conductor that will only be a #12,14 AWG.
I think this was why we are still allowed to run three conductor to a remote out building when no other grounded path's exist.IE. a water pipe
[ September 07, 2003, 08:49 PM: Message edited by: hurk27 ]
jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Re: Neutral Conductors and Equipment Grounds tied together a
Dennis
I think I found it.
The 1937NEC. My reference is Karl Riley, Magnetic Field Guide 2nd Revised Edition
Karl am I giving the correct reference.
Mike P.
Dennis
I think I found it.
The 1937NEC. My reference is Karl Riley, Magnetic Field Guide 2nd Revised Edition
Karl am I giving the correct reference.
Mike P.
Re: Neutral Conductors and Equipment Grounds tied together a
I am making reference to a feeder to a subpanel. I am not addressing equipment grounding conductors.
A three wire cable to a panel will not permit neutral load current to be in parallel with anything except air.
The voltage drop, on a neutral, will be insignificant.
The only reason to float a neutral is to prevent parallel paths for load current.
The supply to a panel can be exactly the same as a service, the neutral/ground is the fault carrying conductor. This is much safer than depending on conduit integrity.
Read section 250.24(5) for accuracy of my opinion.
I am making reference to a feeder to a subpanel. I am not addressing equipment grounding conductors.
A three wire cable to a panel will not permit neutral load current to be in parallel with anything except air.
The voltage drop, on a neutral, will be insignificant.
The only reason to float a neutral is to prevent parallel paths for load current.
The supply to a panel can be exactly the same as a service, the neutral/ground is the fault carrying conductor. This is much safer than depending on conduit integrity.
Read section 250.24(5) for accuracy of my opinion.
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie
I don't see how 250.24(5) validates your opinion here. It says that a grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article.
If you connect the equipment ground conductors to the grounded conductor in a sub panel you would be in violation of this section.
P.S. Congratulations on post 2000!
Bennie
I don't see how 250.24(5) validates your opinion here. It says that a grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article.
If you connect the equipment ground conductors to the grounded conductor in a sub panel you would be in violation of this section.
P.S. Congratulations on post 2000!
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie:
A house with a furnace fed from the main service panel and grounded from it too now homeowner adds a room or two on to this house and uses a sub-panel to pickup the circuits feeding these new rooms these circuits are ran in conduit and one touches the duct work from the existing HVAC this causes a parallel path between the sub-panel and the grounding of the HVAC which probably has a 14 awg ground wire ran to the existing service this 14awg wire is now sharing the neutral current of the sub-panel this will also apply to water pipes too what happens if the new addition has a new electric water heater fed off the new sub-panel installed to pickup the new bathroom the same thing will happen it will create a parallel path but this time the water heater's EGC and the water pipe will be in parallel with the sub-panel's neutral. Ok Ed where's the diagram. Boy I wish I had the soft-ware to do what he can it is always easer to view than to try to explain.
[ September 07, 2003, 10:13 PM: Message edited by: hurk27 ]
Bennie:
Think of it like this.
A house with a furnace fed from the main service panel and grounded from it too now homeowner adds a room or two on to this house and uses a sub-panel to pickup the circuits feeding these new rooms these circuits are ran in conduit and one touches the duct work from the existing HVAC this causes a parallel path between the sub-panel and the grounding of the HVAC which probably has a 14 awg ground wire ran to the existing service this 14awg wire is now sharing the neutral current of the sub-panel this will also apply to water pipes too what happens if the new addition has a new electric water heater fed off the new sub-panel installed to pickup the new bathroom the same thing will happen it will create a parallel path but this time the water heater's EGC and the water pipe will be in parallel with the sub-panel's neutral. Ok Ed where's the diagram. Boy I wish I had the soft-ware to do what he can it is always easer to view than to try to explain.
[ September 07, 2003, 10:13 PM: Message edited by: hurk27 ]
Re: Neutral Conductors and Equipment Grounds tied together a
The change to four wire feeders was made in 1996. It was made by the blue ribbon committee that changed the dryer and range circuit to four wire.
Prior to this three wire SE cable was used to supply other panels in a dwelling. There is many commercial panels with a neutral connected to the panel enclosure.
The neutral/ground conductor prior to 1996, in section 250.152, was permitted to be bare.
This bare conductor could be pulled in a conduit.
There was no concern with parallel neutral current until recently. It can't be for EMF reasons. EMF is not supposed to be a hazard to your health.
The change to four wire feeders was made in 1996. It was made by the blue ribbon committee that changed the dryer and range circuit to four wire.
Prior to this three wire SE cable was used to supply other panels in a dwelling. There is many commercial panels with a neutral connected to the panel enclosure.
The neutral/ground conductor prior to 1996, in section 250.152, was permitted to be bare.
This bare conductor could be pulled in a conduit.
There was no concern with parallel neutral current until recently. It can't be for EMF reasons. EMF is not supposed to be a hazard to your health.
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Mike P. - So the answer was in my book and I had forgotten about it! Well, I wrote it in '94, and these days my memory doesn't always go back that far.
Bennie, all your posts seem to be based on the idea that there is no EGC run with a feed to a subpanel? But you know this is not Code, right? (Except to a separate building that has no metallic connection to the first building.)
Are you saying the Code is wrong, or that you think the NEC says it is OK to bond neutrals and EGCs in a subpanel? I really don't follow you.
Karl
Mike P. - So the answer was in my book and I had forgotten about it! Well, I wrote it in '94, and these days my memory doesn't always go back that far.
Bennie, all your posts seem to be based on the idea that there is no EGC run with a feed to a subpanel? But you know this is not Code, right? (Except to a separate building that has no metallic connection to the first building.)
Are you saying the Code is wrong, or that you think the NEC says it is OK to bond neutrals and EGCs in a subpanel? I really don't follow you.
Karl
karl riley
Senior Member
Re: Neutral Conductors and Equipment Grounds tied together a
Bennie, we are writing simultaneously. You got yours in before mine, so they are out of sequence. Anyhow, the NEC concern with magnetic fields is not health-based. It is heat based. Magnetic fields induce currents/heat in conduits and other metal they are near. Heat is bad, right? The NEC is all about fire and shock.
Since the NEC does not concern itself with either health (other than quick death) or interference with electronics, some of us want to see the Code followed in relation to the heat concern, since it usually also takes care of our health and EMI concern. So please don't give anyone the idea that Bennie says it is OK to bond the neutral bus in a subpanel. Agreed?
Karl
Bennie, we are writing simultaneously. You got yours in before mine, so they are out of sequence. Anyhow, the NEC concern with magnetic fields is not health-based. It is heat based. Magnetic fields induce currents/heat in conduits and other metal they are near. Heat is bad, right? The NEC is all about fire and shock.
Since the NEC does not concern itself with either health (other than quick death) or interference with electronics, some of us want to see the Code followed in relation to the heat concern, since it usually also takes care of our health and EMI concern. So please don't give anyone the idea that Bennie says it is OK to bond the neutral bus in a subpanel. Agreed?
Karl
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