×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

480 Delta, 120/208Y Question

480 Delta, 120/208Y Question

480 Delta, 120/208Y Question

(OP)
Hi all, in the grander scheme of things, I am very new to the electrical engineering field having only a few years of experience under my belt and I've run into a question that none of my superiors have been able to answer, but has been left on my shoulders regardless.  Please forgive me if this sounds naive, but I have a generator in one building that I want to tap off of and feed a neighboring building on the same site with 480V.  I've been told that the service disconnect requires a neutral, but the transformer just downstream of that disconnect is a delta-wye 480V to 120/208V formation.  What do I do with that neutral at the transformer?  I've atatched a sketch (I work so much better with pictures) for reference and if anyone knows of a solution or just has some ideas I would be very grateful!

RE: 480 Delta, 120/208Y Question

Talk to your seniors or look up the NEC ( I presume you are in the NEC world.  This is seeking free design to me. If you have some technical difficulty that would be different.

Rafiq Bulsara
http://www.srengineersct.com

RE: 480 Delta, 120/208Y Question

(OP)
Oh, sorry about that.  Thanks anyways.

RE: 480 Delta, 120/208Y Question

You have a couple of choices.
Extend the generator neutral and ground it at the service disconnect.
Use a four wire delta, 240:480/40 and ground the center tap on the 240:480 phase.
Install an artificial neutral. (Often a last choice when all other options are more expensive.)
But, if the generator feeds grounded neutral loads in the existing building, you need some onsite help to comply with the NEC in regards to grounding systems.
On the other hand if you can reclassify the installation as a sub feed rather than a service entrance some of the issues will go away. I work to the CEC rather than the NEC so I am not sure of the NEC details.
I try to avoid switching neutrals in a transfer switch but sometimes it must be done to comply with codes, specifically one connection between the neutral and ground in a separately derived system.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 480 Delta, 120/208Y Question

Unless the generator belongs to the utility, you're really talking about a generator disconnect, not a service disconnect.

In any case, the requirement for a service disconnect is to disconnect all conductors.  If there is no neutral, then disconnecting the phase conductors is disconnecting all conductors.
 

RE: 480 Delta, 120/208Y Question

I don't see why you need the neutral or why any inspector would require it. The delta primary of the step-down transformer does not require it.

If you decide you do need one, it must come from the generator, not the transformer. You can't create a 480V service neutral inside the new building.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources