If you were to connect two panels to the secondary of the transformer (within 10?-0?) how would you size the grounding electrode conductor from the transformer to the building steel? if you are required to size it according to 250.66 the size of the largest ungrounded conductor is this correct because you essentially have two smaller conductors, or would you base it like you installed a single ocpd and use that conductor size? (ex. 75kva xfmr with two secondary feeds #1 to two panels with 125A mcb in each you run a #6ground to each panel board but what about from the xfmr to steel a #6 also or a #2 based on secondary fla conductors?)
xfmr grounding electrode conductor
- Thread starter Mike01
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- Logan, Utah
Take a look at 250.30(A)(3) If you have multiple sets of secondary conductors you will take the largest equivalent size of the secondary conductors by the largest sum of the corresponding conductors of each set. So if you have two sets of #1 AWG conductors you would have an equivalent size of 3/0. So you would look at Table 250.66 and you are required to have a #4 AWG copper GEC run to the building steel. Also the equipment bonding jumper that is run with the secondary conductor to the first overcurrent device need to be sized off of table 250.66 based on the largest ungrounded secondary conductor. (See 250.30(A)(2))
Chris
Chris I do not disagree with this statement.
But I had a discussion with my lead the other day about this very situation. It has been past pratice to size the EBJ as you would the EGC IE table 250.122. I did not necessary win the debate as it was said that either I or they will have to be retrained in process as this has become kind of a standard and not always easy to change the thought process.
raider1 said:
But I had a discussion with my lead the other day about this very situation. It has been past pratice to size the EBJ as you would the EGC IE table 250.122. I did not necessary win the debate as it was said that either I or they will have to be retrained in process as this has become kind of a standard and not always easy to change the thought process.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Bea said:
Is this not the case with a lot of the training provided in the field today!!!
- Location
- Logan, Utah
Bea said:
I have found this to be true in my area also. This is one of the most common violations that I see when inspecting transformers.
It can be very hard to change the way people have been trained.
Chris
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