I have a 200amp meter loop with a four space sub feed. If I sub feed a 100amp main breaker panel in a de-tached garage, do I need to bond the gounded conductor to the equipment ground bar or is it seperate at that point. It is bonded at the 200amp meter loop and there is no egc ran with the sub feed to the garage. I read 250.32 but still not sure where this fits in. I am thinking it needs to be bonded.
Sub Feed Ground
- Thread starter Samz
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bphgravity
Senior Member
- Location
- Florida
Re: Sub Feed Ground
If you meet the provisions of 250.32(B)(2), you must bond. In short, you treat it like a service and provide a grounding electrode system as well.
If you meet the provisions of 250.32(B)(2), you must bond. In short, you treat it like a service and provide a grounding electrode system as well.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Sub Feed Ground
Samz, can you elaborate on the point in the process at which your confusion starts?
Do you understand why you shouldn't bond the grounding and neutral conductors twice (once @ service, and again @ detached building) unless there are no metallic paths between them? That is key, at least when I think about it.
Once the "whys" are understood, the "whens" and "whats" fall into place.
Samz, can you elaborate on the point in the process at which your confusion starts?
Do you understand why you shouldn't bond the grounding and neutral conductors twice (once @ service, and again @ detached building) unless there are no metallic paths between them? That is key, at least when I think about it.
Once the "whys" are understood, the "whens" and "whats" fall into place.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Sub Feed Ground
As George pointed out the key here is metallic paths between the two structures. If none exist than you may eliminate the EGC between the garage and the meter loop. If a metallic path does exist, say as a phone line for example, than the EGC must be pulled and must be separate from the grounded conductor at the garage. This will prevent a parallel path for the current to flow on the phone line etc. The safest bet would be to simply pull the EGC with the feeder conductors and separate the grounded and grounding conductors at the panel.
As George pointed out the key here is metallic paths between the two structures. If none exist than you may eliminate the EGC between the garage and the meter loop. If a metallic path does exist, say as a phone line for example, than the EGC must be pulled and must be separate from the grounded conductor at the garage. This will prevent a parallel path for the current to flow on the phone line etc. The safest bet would be to simply pull the EGC with the feeder conductors and separate the grounded and grounding conductors at the panel.
- Location
- Massachusetts
Re: Sub Feed Ground
....that are bonded to the grounding system in both buildings or structures.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Sub Feed Ground
You're right Bob, they would need to be bonded to form a parallel path. And if they were properly installed than they would be bonded at both structures. I was making an assumption. Thanks for the correction.
Trevor
You're right Bob, they would need to be bonded to form a parallel path. And if they were properly installed than they would be bonded at both structures. I was making an assumption. Thanks for the correction.
Trevor
- Location
- Massachusetts
Re: Sub Feed Ground
What I posted is part of 250.32(B)(2).
Not sure what you mean by properly installed.
A chain link fence between two structures is a continuous metallic path but is not usually bonded to the structures although it could be and that would make a difference.
Is a phone line bonded to both structures?
Morning Trevor.
What I posted is part of 250.32(B)(2).
I think that many times "bonded to the grounding system in both buildings" is forgotten about when we talk about 250.32(B)
Not sure what you mean by properly installed.
A chain link fence between two structures is a continuous metallic path but is not usually bonded to the structures although it could be and that would make a difference.
Is a phone line bonded to both structures?
Re: Sub Feed Ground
Here's a graphic with some commentary from Mike Holts material.
This subsection added a new requirement and it reads:
(B) Grounded Systems
(2) Grounded (neutral) Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.
The size of the grounded conductor shall not be smaller than the larger of:
(1) That required by 220.22 (maximum unbalanced neutral load), or
(2) That required by 250.122 (equipment grounding conductor size). Figure 250?10
Intent: The new sentence specifies how to size the grounded (neutral) conductor to a building or structure, when an equipment grounding conductor is not run to the separate building or structure.
Author?s Comment: When an equipment grounding conductor is not run to a separate building or structure, the grounded (neutral) conductor must be used to provide the effective fault current path required to clear any line-to-case faults in addition to carrying any unbalanced neutral current.
Roger
[ January 15, 2006, 09:40 AM: Message edited by: roger ]
Here's a graphic with some commentary from Mike Holts material.
This subsection added a new requirement and it reads:
(B) Grounded Systems
(2) Grounded (neutral) Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.
The size of the grounded conductor shall not be smaller than the larger of:
(1) That required by 220.22 (maximum unbalanced neutral load), or
(2) That required by 250.122 (equipment grounding conductor size). Figure 250?10
Intent: The new sentence specifies how to size the grounded (neutral) conductor to a building or structure, when an equipment grounding conductor is not run to the separate building or structure.
Author?s Comment: When an equipment grounding conductor is not run to a separate building or structure, the grounded (neutral) conductor must be used to provide the effective fault current path required to clear any line-to-case faults in addition to carrying any unbalanced neutral current.
Roger
[ January 15, 2006, 09:40 AM: Message edited by: roger ]
Re: Sub Feed Ground
I do understand that if there was an EGC ran with the other conductors and both were bonded that the unbalanced load would be returning on any path including any metallic path that was bonded. Its just hard for me to understand why it wouldn't do ths same thing since it is bonded at the second service. Does it just on the path to the ground rod?
I do understand that if there was an EGC ran with the other conductors and both were bonded that the unbalanced load would be returning on any path including any metallic path that was bonded. Its just hard for me to understand why it wouldn't do ths same thing since it is bonded at the second service. Does it just on the path to the ground rod?
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Sub Feed Ground
If you pull an equipment grounding conductor with the outside feeder, you don't bond at the detached building. The path is:
Neutral screw of receptacle > neutral branch circuit conductor > neutral bar of subpanel > neutral conductor of feeder > neutral bar of service, where the grounding system is bonded and disappears as the current gets to > Transformer XO.
What would the second path for neutral current be, if there were no other metallic paths?
If you pull an equipment grounding conductor with the outside feeder, you don't bond at the detached building. The path is:
Neutral screw of receptacle > neutral branch circuit conductor > neutral bar of subpanel > neutral conductor of feeder > neutral bar of service, where the grounding system is bonded and disappears as the current gets to > Transformer XO.
If an EGC is pulled with the feeder, the grounding electrodes are connected to that, not the neutral conductor, in the detached building. So no neutral current will flow on the ground rod, since they are not connected together (in a direct sense).
Re: Sub Feed Ground
Some of the confusion here may be why there is a ground rod needed at the detached building. I know that that part has me confused
That being said, can we all agree that it is a better installation to run an ECG with the other conductors regardless. Treat the detached building panel as a sub panel, and seperate the neutrals and grounds?
Some of the confusion here may be why there is a ground rod needed at the detached building. I know that that part has me confused
That being said, can we all agree that it is a better installation to run an ECG with the other conductors regardless. Treat the detached building panel as a sub panel, and seperate the neutrals and grounds?
- Location
- Massachusetts
Re: Sub Feed Ground
EGC run with the feeder or not there will always be (or the potential to be) current flowing through the earth between the separate grounding electrode systems.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Sub Feed Ground
Originally posted by iwire:
Not sure what you mean by properly installed.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Sub Feed Ground
How's that? There's nearly zero resistance between them, they're connected through the EGC of the feeder.
- Location
- Massachusetts
Re: Sub Feed Ground
The phone drop to my house looks like heavy 2 wire solid lamp cord.
Have you seen an instance where that would apply?
The phone drop to my house looks like heavy 2 wire solid lamp cord.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Sub Feed Ground
Originally posted by jbwhite:
Some of the confusion here may be why there is a ground rod needed at the detached building. I know that that part has me confused
- Location
- Massachusetts
Re: Sub Feed Ground
There's nearly zero resistance between them, they're connected through the EGC of the feeder. [/QB][/QUOTE]
There's nearly zero resistance between them, they're connected through the EGC of the feeder. [/QB][/QUOTE]
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Sub Feed Ground
It just occurred to me. The detached building predicament is the yen to the yang of 250.52(A)(1).
Yen: We can't really rely on the metal water pipe to interconnect electrodes, because a plumber might come along and stop the continuity.
Yang: We shouldn't rely on a neutral to perform bonding after the service, because a plumber might come along and add a metallic water pipe with continuity to the service.
Can we win?
Not once.
It just occurred to me. The detached building predicament is the yen to the yang of 250.52(A)(1).
Yen: We can't really rely on the metal water pipe to interconnect electrodes, because a plumber might come along and stop the continuity.
Yang: We shouldn't rely on a neutral to perform bonding after the service, because a plumber might come along and add a metallic water pipe with continuity to the service.
Can we win?
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