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 Post subject: 130.3 Ex.1 (2) The circuit is supplied by one Transformer.
PostPosted: Mon Jul 20, 2015 12:01 pm 
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Joined: Mon Jul 20, 2015 11:47 am
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I am reviewing an Arc Flash study.
The Utility is using three single 25kva transformers
for a 75kva 240v delta transformer bank.
Will this installation meet NFPA 70 E Article 130.3 Exception 1?
Are the three single phase transformers provided by the Utility ,
meeting the intent of Paragraph (2)?


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 Post subject: Re: 130.3 Ex.1 (2) The circuit is supplied by one Transform
PostPosted: Mon Jul 20, 2015 4:06 pm 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 439
Location: Wisconsin
rsuhadolc wrote:
I am reviewing an Arc Flash study.
The Utility is using three single 25kva transformers
for a 75kva 240v delta transformer bank.
Will this installation meet NFPA 70 E Article 130.3 Exception 1?
Are the three single phase transformers provided by the Utility ,
meeting the intent of Paragraph (2)?


The exception you mention was last seen in 2009, you really should get a new copy of NFPA70E
This exception also does not exist in the previous version (2012) of NFPA70E. Instead there is a recommendation to look at IEEE1584 for transformers <240V.

So in summary:
Yes three interconnected single phase transformers units are considered to be the same as a single 3-phase transformer. The prohibition is against paralleled 3-phase transformers.
240V secondary transformers need to be considered.


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 Post subject: Re: 130.3 Ex.1 (2) The circuit is supplied by one Transform
PostPosted: Tue Jul 21, 2015 7:49 am 
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We will review again with NFPA 70 E 2015 Table 130.7 (C) (15)(A)(b)


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 Post subject: Re: 130.3 Ex.1 (2) The circuit is supplied by one Transform
PostPosted: Tue Jul 21, 2015 9:46 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 679
Location: Rutland, VT
rsuhadolc wrote:
We will review again with NFPA 70 E 2015 Table 130.7 (C) (15)(A)(b)


I noticed in your original post you mentioned you are reviewing an arc flash study. That implies an actual was done using IEEE 1584 methodology. Therefore, the incident energy levels should have been calculated and therefore you cannot use the NFPA Table mentioned above. See NFPA 70E-2015 130.5(C)

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