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#164265 - 05/29/07 12:21 PM isolating transformer
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
I am installing an isolating transformer with electrostatic sheild for a music recording studio 240 volt(60 amps) in and 240/120 out. it is in a residential house that has no steel. my question is does this sound like proper application/installation for this job(haven't done x-former in ions)i pull 3-#8's(copper)two phases tied to primary (h1+h4 and h4+h10), one ground (to factory provided lug) from new sub panel(feeds non isolated loads) in music room through 3/4" EMT to jbox,then whip into x-former. at x-former i install a double barrel lug to frame of x-former and tie x2 and x3 from secondary to oneside of lug and feed isolated sub-panel neutral from this bonding point. then bond single lug on frame and run to ground bar of my isolated sub-panel and feed isolated sub-panel from x1 and x4. does this sound right? or did i miss something? thanks in advance,
H2o


Edited by watersparkfalls (05/29/07 12:30 PM)

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2014 / 2011 NEC & Related Books and Study Guides
#164290 - 05/30/07 02:51 PM Re: isolating transformer [Re: watersparkfalls]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
H2O Sparks:
Check out the Technical Area for schematics. Scott35 runs a tight ship over there, and that should answer all your needs.
John
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#164299 - 05/30/07 04:51 PM Re: isolating transformer [Re: watersparkfalls]
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
well i've researched my own question and since this is an isolating transformer i will actually use a tap block for x2 and x3 then intentially ground it to earth via ground rod and pull my isolated neutral from here(thus keeping it free from transient noises and keeping it isolated). for my equipment bond i will pull off frame grounding lug from transformer??
still reading....
H2o

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#164300 - 05/30/07 04:54 PM Re: isolating transformer [Re: HotLine1]
watersparkfalls Offline
Member

Registered: 03/08/05
Posts: 210
Loc: Washington...Not DC
john where is this tech area?
thanks
H2o

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#164448 - 06/03/07 04:14 PM Re: isolating transformer [Re: watersparkfalls]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
Go to the main forum page, then scroll down....technical section.......underneath the 'pics' area......
Sorry for the delay; I've been out of town.
John
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#164594 - 06/06/07 05:50 PM Re: isolating transformer [Re: HotLine1]
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
You can't really isolate it from the utility as the isolating transformer will require a primary EGC that will be connected to the case and the secondary grounded conductor will also have to be bonded to the case.
Don
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#164605 - 06/06/07 10:35 PM Re: isolating transformer [Re: resqcapt19]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Isolation transformers do not have a grounded secondary as a general rule. That is the point. IBM used them for the convenience outlets in all of our old mainframe machines. The secondary was completely floating. That actually accomplished 2 things. We never brought a grounded conductor into the computer room panels so that was the only way to get 120v and it also prevented electrocution or overcurrent in any line to ground contact ... at least the first one anyway. The cases of connected equipment still got grounded via the EGC. Usually the line filters in the first piece of plugged in equipment stabilized the voltage at +/- 60v. We tried to keep the customes out of there but an available NEMA 5-15 will get used.
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#164611 - 06/07/07 01:58 AM Re: isolating transformer [Re: gfretwell]
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
 Originally Posted By: gfretwell
Isolation transformers do not have a grounded secondary as a general rule. That is the point.


I do not believe that will be NEC compliant.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#164614 - 06/07/07 05:41 AM Re: isolating transformer [Re: iwire]
ghost307 Offline
Member

Registered: 05/09/05
Posts: 884
Loc: Chicago Illinois USA
Isolation transformers need to have their output referenced to ground just the same way as any other transformer.

NEC says that if it CAN be grounded, it SHALL be grounded.

What doesn't need a ground connection is an "isolated power system" such as is found in a Hospital. But then you've got to have monitoring equipment to tell you when there's a fault in the secondary. There are also a few other very limited exceptions, but isolation transformers aren't among them.
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Ghost307

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#164620 - 06/07/07 09:10 AM Re: isolating transformer [Re: ghost307]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
This was under the covers of listed equipment, not premisis wiring.
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Greg Fretwell

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