proper grounding of a wye-wye transformer to switchgear

[philhanna@comcast.net]

I am designing a switchgear installation (480Y/277) that will be fed by a Utility wye-wye 2500kva transformer. The utility intends on grounding the neutral to a ufer in the vault. They want me to bring my 11 sets of 4-500 kcmil to the transformer and connect the switchgear neutral bus to the switchgear ground bus. If I were to do that, how should I size the ground ring and electrodes at the switchgear and will that cause a problem with the neutral being grounded at two points?

 

[rbalex]

A couple of clarifications to make sure I understand your description. First, the transformer belongs to the utility; second, you are describing the transformer’s secondary neutral that the utility will be grounding.

If the above is true, effectively, the utility is installing the Grounding Electrode Conductor at the transformer and the “connection” they are asking you to make is actually the Main Bonding Jumper. [See Article 100 (Bonding Jumper, Main)].

Assuming all other Equipment Grounding Conductors properly originate at your ground bus, you may not need to do anything else unless there are other intrinsic grounding electrodes present that must be bonded to the Concrete-Encased Electrode (the“Ufer”). [See Sections 250.50 and 250.52] Unless lightning or possibly “Step and Touch” is an issue, you probably don’t need any other “made” grounding electrodes. [250.52(A)(4) to (A)(7)]

 

[philhanna@comcast.net]

proper grounding of a wye-wye transformer to switchgear

Yes, Bob, the transformer belongs to the utility and the neutral is on the secondary side, but they tie the secondary to the primary and to the vault ufer ground. It might help if I could e-mail you a sketch. My e-mail address is in the post.

 

[rbalex]

I would prefer you post the sketch here in the forums since others may want to share their insights.

Even with your added information though, my original response still stands. Tying the primary and secondary neutrals to a common electrode makes no difference.

 

[Smart $]

Yes, Bob, the transformer belongs to the utility and the neutral is on the secondary side, but they tie the secondary to the primary and to the vault ufer ground. It might help if I could e-mail you a sketch. My e-mail address is in the post.

The bearing factor here is the location of the service point.

Please post sketch here, if possible (if not, make it possible :roll

 

[philhanna@comcast.net]

proper grounding of a wye-wye transformer to switchgear

The file upload manager rejects my pdf scan as invalid, so I can't post the sketch. Thank you for your help, Bob.

 

[philhanna@comcast.net]

Smart$-any suggestions for attaching my pdf sketch to the post?

 

[philhanna@comcast.net]

When I right click the insert image icon, it asks for a url. I don't see a way to paste my pdf in the post.

 

[Smart $]

The file upload manager rejects my pdf scan as invalid, so I can't post the sketch. Thank you for your help, Bob.

Smart$-any suggestions for attaching my pdf sketch to the post?

When I right click the insert image icon, it asks for a url. I don't see a way to paste my pdf in the post.

The attachment function "supposedly" permits you to attach a pdf to your post... but I've never had any success doing so... always says failed to upload and never provides a reason why.

Rather than explaining what you have to do, I'll PM you with my email address, send me the pdf via email and I'll post it here in some fashion.

EDIT: On second thought, it appears your user name is your email address. I'll send you an email which you can reply to with the pdf attachment...

 

[philhanna@comcast.net]

That sounds good..Thank you

 

[philhanna@comcast.net]

Graphic courtesy of smart $. Thank you. I am interested in any comments on this proposed grounding/bonding scheme for a new installation.

http://i145.photobucket.com/albums/r204/Smart_S/grounding2.gif[/IMG

 

[philhanna@comcast.net]

Please try this link


http://i145.photobucket.com/albums/r204/Smart_S/grounding2.gif

 

[Smart $]

Please try this link


http://i145.photobucket.com/albums/r204/Smart_S/grounding2.gif

I added MBJ (inadvertently deleted from first graphic) and deleted file at link provided. Here' new edition...

 

[Smart $]

.... I am interested in any comments on this proposed grounding/bonding scheme for a new installation.

If the service point is the line terminals of the gear, as drawn is compliant under all code cycles, I believe.

 

[philhanna@comcast.net]

Thanks for all your help.

 

[Team-MEI]

You may need the two grounds to be at least twenty feet apart. Also, for further reading; please google Sorgel Communicator SC-6 (from 1977).

 

[LarryFine]

That's perfectly fine. There's no metallic connection between the POCO's GEC and yours.

 

[Smart $]

That's perfectly fine. There's no metallic connection between the POCO's GEC and yours.

Question is, would it be compliant if the service point is the xfmr's secondary terminals?

 

[kingpb]

What is the utility company? Grounded wye - Grounded-wye seems especially odd for a utility since it can inherent problems for there system. Usually only see this on a new install were you have interconnections with other systems where you might need to match a phasing.