Transformer, Stepping up.

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dave121

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Are there any rules against using a std. 480x240, dry type, single phase transformer to step up from 240 to 480 v? I've heard they would need to be listed for stepping up. ( not the normal every day step down ) Aside from sizing, and protection of the primary and secondary.

Thanks
 
Discussed in this forum several times, if you search for "step up transformer". In a nutshell though, it's done all the time and the 2014 code now makes mention of the transformer needing to be labeled or listed for that by the manufacturer.
 

From the 2014 code.
450.11(B) Source Marking. A transformershall be permitted to be supplied at the marked secondary voltage, providedthat the installation is in accordance with the manufacturer?s instructions.
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don_resqcapt19 said:

From the 2014 code.
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Finally just got my 2014, haven't had time to look for that yet. Thanks for giving out the section. This has been coming up a lot for me lately, even though we will not likely adopt the 2014 code until 2017 or 18, but the buzz on it has people scrambling a bit. It's done a lot with VFDs, where people get machines with 480V motors but have 208 or 230V supplies and then realize its cheaper to buy a 480V drive and put the transformer on the line side rather than change the motor and buy a VFD rated for twice the current.
 
dave121 said:
Are there any rules against using a std. 480x240, dry type, single phase transformer to step up from 240 to 480 v? I've heard they would need to be listed for stepping up. ( not the normal every day step down ) Aside from sizing, and protection of the primary and secondary.

Thanks
Click to expand...
Interesting that you omitted the kva rating
of the transformer though.
There is no issue with using a transformer to step up but depending upon the va rating you may not like the results as the HV may be lower than you had anticipated and then you ask another question which asked why.
From the 480x240 1ph leads me to believe that it is a machine tool or control power transformer.
 
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