I am working on some roadway lighting that will be fed from an existing 240V-480V single phase utility transformer. The utility has tapped this transformer so it's 480V to ground. I have been told that on a 480V to ground system that the peak voltage is 480V*1.4=672V and this falls into the "over 600V" system which requires over 600V insulation on the conductors and likewise for the equipment ratings. But looking at NEC 300.2(A) it defines the voltage limitations to nominal voltage, not peak voltage, so wouldn't this be consider a nominal 480V system? Am i missing a piece to this puzzle or am i getting incorrect information, or possibly other code sections that might be applicable or supersede 300.2? Thanks in advance,
240-480V transformer
- Thread starter solarEI
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- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
What you've described seems rather odd. My guess is that the system is probably a 3 phase corner grounded Delta. Between either of the phase conductors and the grounded conductor you will have 480 volts.
jtester
Senior Member
- Location
- Las Cruces N.M.
You would not deal in peak voltages, only nominal. So you don't need to worry about being over 600 volts. One caution is to be sure that your gear is rated for 480 volts to ground. Much 277/480 volt stuff is not rated for 480 volts to ground.
Jim T
Jim T
Thanks!! But i still don't think i understand the transformer set up. The utility company said it is a 240/480V single phase transformer tapped so it is a 2-wire system with 480V to ground. If it's a 2-wire system with 480V to ground, how could you get 240V, wouldn't it need to be a 3-wire system? And then wouldn't it be 240V to ground with 480V phase to phase? I have searched all over trying to find a 2-wire wiring diagram but i can't find one anywhere, please help... Thanks in advance,
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
solarEI said:
The transformer has two separate 240V windings.
If they are connected in parallel you have a 2-wire 240V output, one wire may be grounded.
If they are connected in series you have a 2-wire 480V output, one wire may be grounded.
If they are connected in series and the center point is also brought out you have a 3-wire 240/480V output, the center wire may be grounded.
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