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
Rafiq Bulsara
http://www.srengineersct.com
RE: 480 Delta, 120/208Y Question
RE: 480 Delta, 120/208Y Question
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
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"Why not the best?"
Jimmy Carter
RE: 480 Delta, 120/208Y Question
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
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.