I was doing a job for someone in ohio, and I installed a 100a 240v subpanel in this guys detached garage that he is turning into a wood shop. Well when the inspector came to inspect it, she turned it down cause I did not drive a ground rod. I used direct burial cable in the ground, which she also stated that I only had to bury it 18". I found the code for direct burial cable (300.5) which says it must be 24" but I could not fine the article for the ground rod. But I know that there should not be a ground rod cause that would create a parrallel ground ... right?
grounding a sub panel
- Thread starter sparky157
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jxofaltrds
Inspector Mike®
- Location
- Mike P. Columbus Ohio
- Occupation
- ESI, PI, RBO
Re: grounding a sub panel
Sparky
She is correct. I am curious why you would understand paralleled and not grounding/bonding.
Mike P.
Sparky
She is correct. I am curious why you would understand paralleled and not grounding/bonding.
Mike P.
Re: grounding a sub panel
Sparky, you can use an EGC from your main building, and infact, you have to if you have any metalic paths between the buildings. The metalic path could be conduit, water piping, gas piping, or something as small as a phone line.
In the above case you would still supply a GE (rod) and connect it only to the EGC. The nuetral would be isolated from these. (think sub panel in this case)
Roger
Sparky, you can use an EGC from your main building, and infact, you have to if you have any metalic paths between the buildings. The metalic path could be conduit, water piping, gas piping, or something as small as a phone line.
In the above case you would still supply a GE (rod) and connect it only to the EGC. The nuetral would be isolated from these. (think sub panel in this case)
Roger
pierre
Senior Member
- Location
- Westchester County, New York
Re: grounding a sub panel
Sparky157
The reason for the ground rod that is required in 250.32, is for lightning. The equipment grounding conductor that you ran with the conductors is still necessary even with the ground rod that you will be driving at the 'separate structure', which we are all assuming the gararge is in this case.
Remember the ground rod is not going to help the 'effective ground fault path' in order to open an overcurrent protective device ( fuse or breaker).
If you or anyone else who is reading this do not understand this principle FULLY, than this is what you should study before anything else.
Pierre
Sparky157
The reason for the ground rod that is required in 250.32, is for lightning. The equipment grounding conductor that you ran with the conductors is still necessary even with the ground rod that you will be driving at the 'separate structure', which we are all assuming the gararge is in this case.
Remember the ground rod is not going to help the 'effective ground fault path' in order to open an overcurrent protective device ( fuse or breaker).
If you or anyone else who is reading this do not understand this principle FULLY, than this is what you should study before anything else.
Pierre
charlie
Senior Member
- Location
- Indianapolis
Re: grounding a sub panel
Pierre, great answer.
Steve, I don't understand your question. The 1999 and the 2002 editions both have the exception.
Pierre, great answer.
Re: grounding a sub panel
I guess that Pierre's answer confused me a little. If I understand it correctly he's saying that a ground rod is always required at a seperate structure. I was sincere in my question. IMHO, that exception is one of the few clear statements included in 250-32.
thanks
steve
I guess that Pierre's answer confused me a little. If I understand it correctly he's saying that a ground rod is always required at a seperate structure. I was sincere in my question. IMHO, that exception is one of the few clear statements included in 250-32.
thanks
steve
Re: grounding a sub panel
Per the exception we can actually supply a multi-wire branch circuit with out a GE to the seperate building.
This could be two or three OCPD's depending on single or three phase service.
Roger
[ October 04, 2003, 11:37 AM: Message edited by: roger ]
Per the exception we can actually supply a multi-wire branch circuit with out a GE to the seperate building.
This could be two or three OCPD's depending on single or three phase service.
Roger
[ October 04, 2003, 11:37 AM: Message edited by: roger ]
Re: grounding a sub panel
The only reason I was curious about driving a ground rod at the detached garage is that if it ends up being less resistance at the detached garage than at the main service then wouldn't the grounding electrode path be at my detached garage. Isn't that possible, it is only 30' of cable.
The only reason I was curious about driving a ground rod at the detached garage is that if it ends up being less resistance at the detached garage than at the main service then wouldn't the grounding electrode path be at my detached garage. Isn't that possible, it is only 30' of cable.
pierre
Senior Member
- Location
- Westchester County, New York
Re: grounding a sub panel
Sparky157
Answering for Roger, not because he doesn't know the answer, just I am responding first.
Roger meant that at a separate structure, you can run the phase conductors, a neutral and the Equipment Grounding Conductor is not required as long as there is no metallic path back to the building that is feeding this panel (phonewire, plumbing, cablewire, etc..).
The ground rod will not be for EGC purposes, the neutral conductor will serve two purposes. As the Neutral going to the garage, an as EGC back to the source if a groundfault should occur at the garage.
The ground rod is for lightning, not for EGC purposes.
Pierre
Sparky157
Answering for Roger, not because he doesn't know the answer, just I am responding first.
Roger meant that at a separate structure, you can run the phase conductors, a neutral and the Equipment Grounding Conductor is not required as long as there is no metallic path back to the building that is feeding this panel (phonewire, plumbing, cablewire, etc..).
The ground rod will not be for EGC purposes, the neutral conductor will serve two purposes. As the Neutral going to the garage, an as EGC back to the source if a groundfault should occur at the garage.
The ground rod is for lightning, not for EGC purposes.
Pierre
- Location
- Massachusetts
Re: grounding a sub panel
You can add as many ground rods as you like, you could drive a rod for every outlet in you house and run a wire from each rod to each EGC in each outlet box.
A place where this might happen for real is site lighting poles, often the spec calls for ground rods at each pole and you tie it onto the EGC at each pole.
It could be, but what would it hurt if it was?
You can add as many ground rods as you like, you could drive a rod for every outlet in you house and run a wire from each rod to each EGC in each outlet box.
A place where this might happen for real is site lighting poles, often the spec calls for ground rods at each pole and you tie it onto the EGC at each pole.
Re: grounding a sub panel
Sparky, to put a picture to the sole reason for the ground rod.
As Pierre and Bob point out, the "rod" is only for lightning and surges. A rod would serve no purpose in safety at our voltages and in fact can create hazzards if the service neutral is not intact to provide a fault clearing path to source.
Roger
Sparky, to put a picture to the sole reason for the ground rod.
As Pierre and Bob point out, the "rod" is only for lightning and surges. A rod would serve no purpose in safety at our voltages and in fact can create hazzards if the service neutral is not intact to provide a fault clearing path to source.
Roger
Re: grounding a sub panel
I have four different scenarios with my interpretation regarding supplying power to a seperate structure, please comment and correct me if I'm wrong.
(1) The seperate structure is fed with ONE multi wire branch circuit that includes a grounded and grounding conductor. Grounded and grounding circuits are not bonded and Ground rod NOT required at seperate structure. 250-32.(a)Exception
(2) The seperate structure is fed with one 3 wire feeder circuit and no metallic path exists between grounding systems of each building. Main disconnect and Ground rod(s) IS required at seperate structure and grounded and grounding conductors to be bonded together at seperate structure along with panel enclosure and ground rod(s). 250.32(b(2)
(3) The seperate structure (under single management only) is fed with more than one circuit with remote disconnecting means. The feed circuits must include a grounded and grounding conductor. Grounded and grounding circuits are kept seperate. Ground rod(s) IS required and bonded (in required enclosure) to all grounding conductors and any non-current carrying equipment, interior metal piping and structural frames in the seperate structure. 250.32(d)
(4) A three wire feed is not allowed if there is a metallic path between the two grounding circuits in each structure.
I edited my original post after a weekend of studying 250-32 and re-reading definitions. I don't think that I'm the only one who finds this section un-clear. I understand how important it is to have a properly installed ground system.
Your response is appreciated.
Steve
[ October 07, 2003, 10:15 AM: Message edited by: hillbilly ]
I have four different scenarios with my interpretation regarding supplying power to a seperate structure, please comment and correct me if I'm wrong.
(1) The seperate structure is fed with ONE multi wire branch circuit that includes a grounded and grounding conductor. Grounded and grounding circuits are not bonded and Ground rod NOT required at seperate structure. 250-32.(a)Exception
(2) The seperate structure is fed with one 3 wire feeder circuit and no metallic path exists between grounding systems of each building. Main disconnect and Ground rod(s) IS required at seperate structure and grounded and grounding conductors to be bonded together at seperate structure along with panel enclosure and ground rod(s). 250.32(b(2)
(3) The seperate structure (under single management only) is fed with more than one circuit with remote disconnecting means. The feed circuits must include a grounded and grounding conductor. Grounded and grounding circuits are kept seperate. Ground rod(s) IS required and bonded (in required enclosure) to all grounding conductors and any non-current carrying equipment, interior metal piping and structural frames in the seperate structure. 250.32(d)
(4) A three wire feed is not allowed if there is a metallic path between the two grounding circuits in each structure.
I edited my original post after a weekend of studying 250-32 and re-reading definitions. I don't think that I'm the only one who finds this section un-clear. I understand how important it is to have a properly installed ground system.
Your response is appreciated.
Steve
[ October 07, 2003, 10:15 AM: Message edited by: hillbilly ]
Re: grounding a sub panel
Steve, if we are supplying the separate building with a branch circuit, single or multi-wire
there would not be a panel at the building. The branch circuit would go directly to the utilization equipment or receptacle.
This could cause a parallel path between the metalic path and the grounded conductor if a fault occured.
If I'm misinterpreting your scenarios I apologize.
Roger
[ October 05, 2003, 01:00 PM: Message edited by: roger ]
Steve, if we are supplying the separate building with a branch circuit, single or multi-wire
there would not be a panel at the building. The branch circuit would go directly to the utilization equipment or receptacle.
buildings
This could cause a parallel path between the metalic path and the grounded conductor if a fault occured.
If I'm misinterpreting your scenarios I apologize.
Roger
[ October 05, 2003, 01:00 PM: Message edited by: roger ]
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