What is the requirement for grounding of a 15Kw permenently installed generator on a residence. The generator is already grounded with a factory installed #8 equipment grounding conductor from the transfer switch, but the manufacturers instructions require an additional bonding connection of a #12 be connected to a ground rod. Sounds like Mikes favorite pet peeve
generator grounding
- Thread starter careco1
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grandpapastu
Member
Re: generator grounding
Is a connection, including that of a solidly grounded neutral, between the two systems present?
A simple way to determine this is to examine the transfer switch.
Reason I ask is that the code is very specific about the grounding electrode used for seperately derived systems.
I have here the NFPA 70 2002 Edition and it seems to me that according to the NEC 2002 provisions of the Art. 250.30 (A)(2)(a) applies:
Single seperately derived system. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived phase conductors...
Research it a bit of course; but, an 8 AWG GEC sounds a lot better than a 12 AWG.
[ July 18, 2005, 10:35 PM: Message edited by: grandpapastu ]
Is a connection, including that of a solidly grounded neutral, between the two systems present?
A simple way to determine this is to examine the transfer switch.
Reason I ask is that the code is very specific about the grounding electrode used for seperately derived systems.
I have here the NFPA 70 2002 Edition and it seems to me that according to the NEC 2002 provisions of the Art. 250.30 (A)(2)(a) applies:
Single seperately derived system. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived phase conductors...
Research it a bit of course; but, an 8 AWG GEC sounds a lot better than a 12 AWG.
[ July 18, 2005, 10:35 PM: Message edited by: grandpapastu ]
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
Re: generator grounding
Also remember that if the generator and service neutrals are solidly tied together (i.e., not switched), the generator is not a separately-derived system.
Edited to apologize to Stu for redundancy.
[ July 18, 2005, 10:56 PM: Message edited by: LarryFine ]
Also remember that if the generator and service neutrals are solidly tied together (i.e., not switched), the generator is not a separately-derived system.
Edited to apologize to Stu for redundancy.
[ July 18, 2005, 10:56 PM: Message edited by: LarryFine ]
Re: generator grounding
I might be wrong but it sounds as if the manuf. wants an external case ground on the tranfer going back to the system "earth" ground. I have run into this where electronic controls are installed in an industrial setting. Especially scales, etc. Seems like it would create a ground loop or alternate path to ground, but I guess the manuf. covers the warranty.
I might be wrong but it sounds as if the manuf. wants an external case ground on the tranfer going back to the system "earth" ground. I have run into this where electronic controls are installed in an industrial setting. Especially scales, etc. Seems like it would create a ground loop or alternate path to ground, but I guess the manuf. covers the warranty.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: generator grounding
It sounds to me like the manufacturer wants to make sure there's little potential for potential ( :roll: ) difference between the genrator case and the surrounding earth.
That the manufacturer specs the rod in the instructions makes the discussion moot. If it's required, it's required.
It sounds to me like the manufacturer wants to make sure there's little potential for potential ( :roll: ) difference between the genrator case and the surrounding earth.
That the manufacturer specs the rod in the instructions makes the discussion moot. If it's required, it's required.
Dnkldorf
Senior Member
Re: generator grounding
I thought the ground rod installation hinged on 2 things.
The transfer switching the nuetral, and the bonding jumper inside the generator.
If the generator is internally bonded, and the transfer swich switches the nuetral, then a ground rod would be required at the generator loctaion.
But if the bonding jumper is removed from the generator, and the nuetral in the transfer switch is unswitched, then no ground rod is required.
Or do I have this backwards?
I also thought either way, a EGC is required.
Dnk...
I thought the ground rod installation hinged on 2 things.
The transfer switching the nuetral, and the bonding jumper inside the generator.
If the generator is internally bonded, and the transfer swich switches the nuetral, then a ground rod would be required at the generator loctaion.
But if the bonding jumper is removed from the generator, and the nuetral in the transfer switch is unswitched, then no ground rod is required.
Or do I have this backwards?
I also thought either way, a EGC is required.
Dnk...
busman
Senior Member
- Location
- Northern Virginia
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- Master Electrician / Electrical Engineer
Re: generator grounding
Sorry to dig up an old post, but I was searching for information on the requirement for permanent generators at a residence to have a ground rod (when they are not an SDS). I am wondering if this is because the generator could be considered a separate structure under 250-32? Would this explain the ground rod?
Anyone have experience with this?
Thanks,
Mark
Sorry to dig up an old post, but I was searching for information on the requirement for permanent generators at a residence to have a ground rod (when they are not an SDS). I am wondering if this is because the generator could be considered a separate structure under 250-32? Would this explain the ground rod?
Anyone have experience with this?
Thanks,
Mark
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: generator grounding
There is no NEC requirement to drive a ground rod at this generator. It may be required by the instructions that came with the generator.
You may drive one and connect it to the frame of the generator, but it won't do anything much. It is a supplementary electrode.
There is no NEC requirement to drive a ground rod at this generator. It may be required by the instructions that came with the generator.
You may drive one and connect it to the frame of the generator, but it won't do anything much. It is a supplementary electrode.
pierre
Senior Member
- Location
- Westchester County, New York
Re: generator grounding
"I thought the ground rod installation hinged on 2 things.
The transfer switching the nuetral, and the bonding jumper inside the generator.
If the generator is internally bonded, and the transfer swich switches the nuetral, then a ground rod would be required at the generator loctaion.
But if the bonding jumper is removed from the generator, and the nuetral in the transfer switch is unswitched, then no ground rod is required."
Dnkldorf, you have this correct.
The neutral conductor has to be switched at the transfer switch in order for the generator to be considered a separately derived system.
"I thought the ground rod installation hinged on 2 things.
The transfer switching the nuetral, and the bonding jumper inside the generator.
If the generator is internally bonded, and the transfer swich switches the nuetral, then a ground rod would be required at the generator loctaion.
But if the bonding jumper is removed from the generator, and the nuetral in the transfer switch is unswitched, then no ground rod is required."
Dnkldorf, you have this correct.
The neutral conductor has to be switched at the transfer switch in order for the generator to be considered a separately derived system.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: generator grounding
Edit to fix quote
[ January 02, 2006, 04:48 PM: Message edited by: georgestolz ]
I think a ground rod would only be permitted if the structural metal electrode or water pipe electrode were non-existent or not available. 250.30(A)(4)(3).
Edit to fix quote
[ January 02, 2006, 04:48 PM: Message edited by: georgestolz ]
ty
Senior Member
- Location
- 3rd Rock from the Sun
Re: generator grounding
Would it be better to say that it is determined by the generator neutral being bonded or not to consider it a SDS or not, and because of that, it is determined weather or not the neutral is to be switched or not in the transfer switch??
I keep hearing this explanation lately. And with all due respect, is this the proper way to explain it??
Would it be better to say that it is determined by the generator neutral being bonded or not to consider it a SDS or not, and because of that, it is determined weather or not the neutral is to be switched or not in the transfer switch??
- Location
- Massachusetts
Re: generator grounding
I would have to say your right.
pierre
Senior Member
- Location
- Westchester County, New York
Re: generator grounding
George
The OP says this is for a dwelling.
In order to have a separately derived system, the neutral conductor has to be not "solidly connected". This is also how to determine whether the neutral is bonded to the EG at the generator. The only way to determine all of this is to know if the neutral is switched or not at the transfer switch. So, the transfer switch is the determining factor here.
George
The OP says this is for a dwelling.
In order to have a separately derived system, the neutral conductor has to be not "solidly connected". This is also how to determine whether the neutral is bonded to the EG at the generator. The only way to determine all of this is to know if the neutral is switched or not at the transfer switch. So, the transfer switch is the determining factor here.
pierre
Senior Member
- Location
- Westchester County, New York
Re: generator grounding
"Bob
ARROGANT HACK DIY WANABE ELECTRICIAN
Massachusetts"
Bob
you should have told us this from the beginning
"Bob
ARROGANT HACK DIY WANABE ELECTRICIAN
Massachusetts"
Bob
you should have told us this from the beginning
- Location
- Massachusetts
Re: generator grounding
Saying it is the transfer switch is putting the cart before the horse.
Pierre I believe Ty was correct the bond or lack of bond at the generator determines SDS or not.
Saying it is the transfer switch is putting the cart before the horse.
- Location
- Massachusetts
Re: generator grounding
Sorry for my lack of honesty.
ROTFLOriginally posted by pierre:
"Bob
ARROGANT HACK DIY WANABE ELECTRICIAN
Massachusetts"
Bob
you should have told us this from the beginning
Sorry for my lack of honesty.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: generator grounding
Pierre, the aspect of the statement I was trying to cast light on (for my own benefit), was what type of grounding electrode is called for by the requirements for an SDS (when an SDS exists).
To say "drive a ground rod and you're done" doesn't seem accurate.
Pierre, the aspect of the statement I was trying to cast light on (for my own benefit), was what type of grounding electrode is called for by the requirements for an SDS (when an SDS exists).
I was saying that the original system's water pipe electrode is to be used when it is available, per 250.30(A)(4)(3).
To say "drive a ground rod and you're done" doesn't seem accurate.
busman
Senior Member
- Location
- Northern Virginia
- Occupation
- Master Electrician / Electrical Engineer
Re: generator grounding
My original question was - can the generator be considered a separate structure (like a light pole) and therefore require it's own electrode, even if it is not an SDS? There has been a lot of discussion of whether it is an SDS or not. I have not heard anyone yet address whether a genset can be considered a separate structure under 250-32?
Thanks,
Mark
My original question was - can the generator be considered a separate structure (like a light pole) and therefore require it's own electrode, even if it is not an SDS? There has been a lot of discussion of whether it is an SDS or not. I have not heard anyone yet address whether a genset can be considered a separate structure under 250-32?
Thanks,
Mark
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