hey moderators,I am happy to finally be here as I have been a guest/lurker for too long. I have an easy question you have been through before. We are installing a number of mini-power zone,single phase, 25 kva load centers. Fed from the busway. The contention is certain individuals feel it is unnessary to exothermic bond the transfomers sec. to the buiding steel. They say the equipment ground is sufficient to connect to as it runs back to the bus equipment ground terminal. I am asking for validation as code references are considered not related to the occupancy. Your opinion would be helpful as I try to convince the supervisor it is nessasary. Thank you for your input.
mini-load center bonding
- Thread starter Phaulty
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Welcome to the forum. I believe you are correct as the transformer is an separately derived system and must be connected to the electrode system. I will have to search for the article and perhaps someone else will have it before I find it.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I believe 250.30 is what you need-- 250.30 (A)(4) is for grounding electrode
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Am I correct in interpreting that even "Exception No. 2 to (1) and (2):" there would not allow an EGC rather than a GEC to be used to supply the ground bond for the panel?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I am not sure what it means, to be perfectly honest.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
I am not sure what it means, to be perfectly honest.
Whew! It is not just me. I read it 3 times and gave up.
I think this is an excellent question.
My first reply was that an separate grounding electrode conductor to a suitable electrode was needed for the transformer secondary.
I always thought exception 2 applied only to mini-power zones that were used as service equipment, however, on closer read, the exception states in "listed equipment suitable as service equipment".
IMO, which could be incorrect if the OP's mini-zone equipment is listed as suitable for service equipment and, if his equipment grounding conductor is sized as noted in the exception, the EGC can be used as the GEC.
side note to OP: The only time I know that the GEC termination must be exothermic is covered in 250.68(A) Exception 2.
My first reply was that an separate grounding electrode conductor to a suitable electrode was needed for the transformer secondary.
I always thought exception 2 applied only to mini-power zones that were used as service equipment, however, on closer read, the exception states in "listed equipment suitable as service equipment".
IMO, which could be incorrect if the OP's mini-zone equipment is listed as suitable for service equipment and, if his equipment grounding conductor is sized as noted in the exception, the EGC can be used as the GEC.
side note to OP: The only time I know that the GEC termination must be exothermic is covered in 250.68(A) Exception 2.
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Gus, how is that gonna fly given this?
250.121 Use of Equipment Grounding Conductors. An
equipment grounding conductor shall not be used as a
grounding electrode conductor.
Thanks Derek..,,,,,
I have now flip-flopped again
Reading the exception for the 4th or 5th time, it appears a grounding electrode conductor would need to be present.
(although it does mention from the service or feeder equipment).
I guess a mini-zone that had a supply grounding electrode (such as actual service equipment) would qualify.
(I hate 'exceptions')
I have now flip-flopped again
Reading the exception for the 4th or 5th time, it appears a grounding electrode conductor would need to be present.
(although it does mention from the service or feeder equipment).
I guess a mini-zone that had a supply grounding electrode (such as actual service equipment) would qualify.
(I hate 'exceptions')
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Except for ones that allow what you need to do to make things work?:lol:
I guess there is such a thing as an exceptional exception. :blink:
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Thanks Derek..,,,,,
I have now flip-flopped again
Reading the exception for the 4th or 5th time, it appears a grounding electrode conductor would need to be present.
(although it does mention from the service or feeder equipment).
I guess a mini-zone that had a supply grounding electrode (such as actual service equipment) would qualify.
(I hate 'exceptions')
I think that section has more exceptions than rules.:rant:
The best option I can think of is to ban Goldy for asking this headache question....
Better yet: Tar and the feather the guy.
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Would you consider diluted bitumen instead?
That is apparently an exception to the laws regulating oil pipelines and it sets up much like tar when the solvent evaporates.
Also, no feathers from endangered species please.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I found this in the handbook but not sure it pertains to except. 2
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
I found this in the handbook but not sure it pertains to except. 2
That looks like a 647 install to me.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Yep it is and I am wondering if the OP is involved with that and that is why it came up.
I have no idea what a mini-power zone is all about
I have no idea what a mini-power zone is all about
- Location
- Illinois
- Occupation
- retired electrician
Prior to the 2011 code, I could see no reason why you could not unsize the primary EGC and use it both as the primary EGC and the GEC for the secondary of the transformer. Yes, you would have to comply with the rules for both conductors, but it was doable...now comes the 2011 code and they specifically tell us that you cannot use the EGC as a GEC.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
So Don do you know what the exception#2 in 250.30(A)(4) is all about
- Location
- Illinois
- Occupation
- retired electrician
The main rule in (A)(4) requires the use of a local water pipe or local building steel as the SDS grounding electrode. The exception permits you not to use those local electrodes and in place of that run a GEC to the building grounding electrode if the SDS "originates" in the service equipment. However it is not completely clear. I read it as permitting the SDS to be remote from the service equipment and running the GEC to the service equipment. I think that may not be what the intent is. I think the intent may be that the SDS is physically installed in the service equipment. Sometimes you will have a 480 volt service and in one of the sections you will have a transformer and 208/120Y panel...that may be what the section intends.
robbietan
Senior Member
- Location
- Antipolo City
I have the same interpretation here
- Status