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.