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
Paul, 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.
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)
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Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!