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#30754 - 10/27/03 02:24 PM Separately Derived System  
SJT  Offline
Joined: Jul 2002
Posts: 241
In a large industrial facility where you have transformers through-out the buildings, is each transformer considered separately derived? These would be a typical 45-100 KVA, with 480 primary and 110/208 secondary. The only place you bond the nuetral and ground would be at the main service. All panels after that, the nuetal bars and equipment grounds would be separate, right? An engineer wanted UPS panels treated like Main panels, and I was telling him that you have to treat them like sub panels. Just because a UPS feeds a panel, it's not the same as a separately derived system. It would be great if some one could clarify this. These transformers would all be in the same building. Thanks

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#30755 - 10/27/03 02:38 PM Re: Separately Derived System  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
The transformers are SDS and require a neutral to ground bond on the secondary side. UPS systems are, in general, also SDS and require neutral to ground bonds on the load side.


#30756 - 10/27/03 02:43 PM Re: Separately Derived System  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Are there cases in the U.S. where with a wye-wye xfmr you might ground the secondary neutral by connecting it to the primary neutral, rather than direct to ground?

#30757 - 10/27/03 04:18 PM Re: Separately Derived System  
George Corron  Offline
Joined: May 2001
Posts: 717
Lorton, Va USA
What is it about YOU and sticky questions???
Danged Brit troublemaker!!!!!!

Long contentious argument about primary/secondary applications. Yes, there are those types applications though most inside wireman never get into them.

Wye/Wye tend to get connected in the transformer and yes, they are the same as bolted together in these apps. Some engineers claim that the procedure is proper, and I have been involved in curing the subsequent problems by separation.

Regardless the code (seems) is clear that it is an SDS, and it appears grounded properly even though both ground to case. This, of course, renders so much current flow between the two as to render your suppression technique nearly useless, and your coordination practically impossible.

The correction is to isolate in the transformer (whichs SEEMS to be a violation of the NESC) and bond the secondary ONLY at the building served.

This flies in the face of most POCO manuals and unless you have the authority (it was nice that when I found this problem I was in that position) it is difficult to isolate the two and still have a meter in your installation.

Again, sticky question @@#$%$%^^@$ Redcoat.

#30758 - 10/27/03 08:54 PM Re: Separately Derived System  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
This topic comes up so often, that it might be a benefit for all of us if I compile as much information possible, plus draw some Schematics for several Scenarios, then post in the Technical Reference area.

Any information that memebrs can supply to me will be greatly appreciated!

I am looking for anything regarding the topic of SDS's; Codes, Best for UPS, anything at all!

Will use information that has been successfully debunked in said presentation post.

Send information to me via E-Mail by using the E-Mail icon at top of this message.
(FYI: address is adst at pacbell dot net)

Please begin the message's subject with "Per ECN Topic of SDS", and include your name/user name. (p.s. don't "Quote" the text as I have done in the above example)

I ask you to do this so your messages get filtered into a "Good Place" [Linked Image]



Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#30759 - 10/28/03 01:44 PM Re: Separately Derived System  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
It's all of you Colonials causing the problems! [Linked Image] Nothing but trouble ever since that little disagreement over some tea... [Linked Image]

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