I have a situation where the source is 120/240 and the load is about 600 feet away. I was considering stepping the voltage up to 480 and then dropping it down to 120/240 at the load. The real queston is it legal to pull the two 480 legs in PVC, Bond the transformer with one ground rod at the load and the neutral with another establishing a isolated system. The load is 200A at 120/240 so one can see the root of the question due to voltage drop and wire size. (Given seperation of the Ground rods) Normally I would say the neutral would have to be pulled thru at the sizing for the unbalanced load and the ground would have to be contigious.
Is contigious neutral required when stepping up voltage and stepping down
- Thread starter wsamuel
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Your source neutral would not need to be run to the secondary location, in fact, it would not even need to be present at your source (step up) transformer.
An equipment grounding conductor would need to be installed with your 480v conductors to provide an equipment grounding means for your step down transformer.
Your step-down transformer secondary would need to be wired per 250.30.
An equipment grounding conductor would need to be installed with your 480v conductors to provide an equipment grounding means for your step down transformer.
Your step-down transformer secondary would need to be wired per 250.30.
As Gus said...
240V 2W w/EGC > PRI{SU-XFMR}SEC > 480V 2W w/EGC > PRI{SD-XFMR}SEC > 120/240 3W w/SSBJ to disconnecting means (DM). GEC to XFMR or DM Neutral or Ground Bus. System bonding jumper (SBJ, not SSBJ) between neutral and ground in same enclosure as GEC connection.
240V 2W w/EGC > PRI{SU-XFMR}SEC > 480V 2W w/EGC > PRI{SD-XFMR}SEC > 120/240 3W w/SSBJ to disconnecting means (DM). GEC to XFMR or DM Neutral or Ground Bus. System bonding jumper (SBJ, not SSBJ) between neutral and ground in same enclosure as GEC connection.
fmtjfw
Senior Member
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- Fairmont, WV, USA
W = wire(s)I'm also a computer programmer and I have no idea what your post meanshmy:
w/ = with
EGC = equipment grounding conductor
> = connection
PRI = transformer primary
SU = step up
XFMR = transformer
SEC = transformer secondary
SD = step down
SSBJ = supply-side bonding jumper
SBJ =system bonding jumper
GEC = grounding electrode conductor
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Except under standard mathematical notation and programming language notation it should have been "--->" instead of ">".
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Feel free to substitute when you write it... :happyyes:
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
What you are missing in this plan is there would not be a low impedance fault path back to the source for a fault at the primary of the transformer (granted if everything else was done per code it would likely clear thru the GES, but this would not be code compliant). I have thought about using transformers for long wire runs over and over throughout the years and I have yet to find a situation where it is cost effective. Aluminum conductors are cheap, especially now........ If you did do this, why not go all the way to 600?
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- Placerville, CA, USA
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- Retired PV System Designer
At least the long run EGC would only have to be sized for the primary ( higher voltage) current source and not the secondary (lower voltage) current at the remote end, since the secondary fault clearing path is entirely local to the remote end.
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Perhaps, perhaps not. Depends on whether there is any secondary OCP for the step-up transformer. If there isn't, the EGC has to be sized per the step-up primary OCP.
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
Hmmm interesting: Despite have contemplated this a number of times, never got far enough along to consider what transformer and conductor protection would be required. Since the situation in the OP is single phase (and even in a three phase situation you would likely go delta-delta), you could go directly from the step up secondary to the step down primary with no OCP at all. IF sized properly, you could protect everything with the primary OCPD. IF this was the case, how do you size the "long run" EGC? Just by using 250.122 on the OCPD in front of the step up because there is no code section saying you can adjust by the turns ratio of the transformer I suppose?
That's how I look at it...
However, don't forget the EGC is not required to be larger than the circuit conductors.
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