When bonding and grounding transformers

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joeyww12000

joeyww12000

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Chatsworth GA
When you guys bond and ground your transformers what is your normal procedure? Lets say its just a small 45kva 480 to 120/208v. I take from XO a GEC to building steel or proper GE, bonding jumper to case frame, neutral conductor to 120/208 panel. From case frame EGC with transformer feeders, main system bonding jumper with derived phase conductors to 120/208panel. The reason for asking is foreman told me I needed to take my GEC from building steel to case frame instead of XO. Im not sure if he's wrong because it's bonded anyway when you install a bonding jumper from XO to case frame, but I dont think the way I do it is wrong either? I just get alot of different ways to do things from different people and I know there are more than one way to skin a cat, but I like to know my way is right to.
 
IMO the NEC requires the GEC to go directly to XO or directly to the grounded terminal bus or the first disconnecting means, whichever location the system bonding jumper is installed.

See 250.32(A)(3).
 
250.30(A)(1) permits the system bonding jumper to be installed at any single point on the SDS from the source to the first system disconnect.
250.30(A)(3) [last sentence], requires the connection of the GEC to be at the same location you choose to make the connection.

It can be made at either location.
 
Here's a graphic to depict what Pierre posted regarding 250.30(A)(3):

1113853482_2.jpg
 
Pierre C Belarge said:
It can be made at either location.
Click to expand...

I agree, but in either location the GEC can not go to the 'case' it must go to the grounded conductor. :smile:

However I did not realize that the bonding could be anywhere from the source to the first disconnect, I thought is was one place or the other. Thanks.
 
As in Mike's graphic the GEC can be connected at the same point where the system bonding jumper is connected. From the wording that would be on either end.

250.30(A)(3) Grounding Electrode Conductor, Single Separately 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 and shall be used to connect the grounded conductor of the derived system to the grounding electrode as specified in 250.30(A)(7). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected.
Click to expand...
 
I picture the GEC termination can be literally like the graphic in post #6, on the equipment ground bus/frame.

Check out the exception #1 to 250.30(A)(3), this graphic supports the termination to be on the equipment grounding terminal when the bonding jumper is a wire type:

1113857619_2.jpg
 
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