Hello everyone. I don't believe that I have ever posted here before but I am stuck and need some help. I am considering using an auto-transformer to boost a single phase 240 volt circuit for a sign to 277 volts. Section 210.9 appears to prohibit this. Is there any way to make it work? I am feeding from a 120/240 volt single phase supply so I can't connect the service neutral to my auto transformer. Does the 277 volt branch have to have a grounded neutral? Thanks for your help!
Boost 240 to 277 Single Phase.
- Thread starter xlx
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Thanks Larry! It looks like I will be buying a standard transformer! 120 is not practical as the run is +- 500' and the sign company has specified a 3% voltage drop. The load is a large sign with (24) 250 watt metal halide ballasts. They run about 1.1 amps each at 277. Add a control circuit, A clock and some overhead and I plan on providing 40 amps.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
One more thing: with such a long run, you should transmit the highest voltage you can for the least voltage drop, so I suggest boosting the voltage as close to the source as you can, and not at the load end.
Added: For that matter, if you can, step up the 240v at the source to, say, 600v for the long run, and then from 600v down to any voltage you like at the load, even 120/240v. Don't forget to bond at the load end.
Added: For that matter, if you can, step up the 240v at the source to, say, 600v for the long run, and then from 600v down to any voltage you like at the load, even 120/240v. Don't forget to bond at the load end.
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