I know this issue has been discussed before but I need a little more clarification. I am currently working as a helper on a commercial job where we are installing a 30KVA transformer. The guy I am working with wants to install a ground rod for the GEC. with no connection to the service GEC system. Is this a violation? How would one make such a connecition?
Transformer GEC.
- Thread starter jes25
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mikeames
Senior Member
- Location
- Gaithersburg MD
- Occupation
- Teacher - Master Electrician - 2023 NEC
Re: Transformer GEC.
Is the building steel unavailable?
Is the building steel unavailable?
- Location
- Illinois
- Occupation
- retired electrician
Re: Transformer GEC.
First 250.30(A)(7) requires the use of "local" building steel or metal water piping system as the SDS grounding electrode. If neither of these are available, you must use any other electrode specified in 250.52(A)(2). There is no requiment that you install a bonding jumper back to the building or service grounding electrode system. They SDS and the building grounding electrode will be bonded together by the SDS primary EGC.
As far as the size of the SDS grounding electrode conductor it is sized per the rules in 250.66, just like for the service.
Don
First 250.30(A)(7) requires the use of "local" building steel or metal water piping system as the SDS grounding electrode. If neither of these are available, you must use any other electrode specified in 250.52(A)(2). There is no requiment that you install a bonding jumper back to the building or service grounding electrode system. They SDS and the building grounding electrode will be bonded together by the SDS primary EGC.
As far as the size of the SDS grounding electrode conductor it is sized per the rules in 250.66, just like for the service.
Don
dana1028
Senior Member
- Location
- San Francisco Bay area
Re: Transformer GEC.
You indicate the SDS and the building grounding electrode will be bonded together by the SDS primary EGC....sounds reasonable...except the primary EGC is sized per T250.122 and all other electrode conductors are sized per T250.66.
Everywhere else in the code, even in 250.104(A), this bonding is sized per T250.66....how is that this interconnection of the electrodes for the SDS and the building are permitted to be sized per T250.122?
I know if the building steel is effectively grounded there is already a satisfactory bond back to the building electrode system; I'm considering the situation of having to use a ground rod where bldg. steel and water are not avail.
Don I'm a bit confused; I always thought I had to bond back to the building service because of 250.58 [2002].
You indicate the SDS and the building grounding electrode will be bonded together by the SDS primary EGC....sounds reasonable...except the primary EGC is sized per T250.122 and all other electrode conductors are sized per T250.66.
Everywhere else in the code, even in 250.104(A), this bonding is sized per T250.66....how is that this interconnection of the electrodes for the SDS and the building are permitted to be sized per T250.122?
I know if the building steel is effectively grounded there is already a satisfactory bond back to the building electrode system; I'm considering the situation of having to use a ground rod where bldg. steel and water are not avail.
- Location
- Illinois
- Occupation
- retired electrician
Re: Transformer GEC.
Dana,
250.58 does not define "effectively bonded together". It is my opinion that the primay EGC provides the required bonding. What god would a larger bonding conductor do?
Don
Dana,
250.58 does not define "effectively bonded together". It is my opinion that the primay EGC provides the required bonding. What god would a larger bonding conductor do?
Don
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