In an industrial setting with a long metering history of loads can the neutral side conductor of a 12470-480Y/277 solidly grounded transformer be reduced to less than the phase conductors? Typically the phase load is 1200-1800 amps, typically within 5% balanced, and the neutral is less than 75 amps. The neutral load is majority lighting and less than 10% harmonics in the neutral current. The phase loads are motors, VSDs and the majority is 480-208Y/120 volt transformers.
Transformer neutral
- Thread starter bibell
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Cold Fusion
Senior Member
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I would be curious why one would want to reduce the size of the neutral of an existing installation.
But as to your question:
From a design standpoint (not even looking at the code):
As you said, the system is solidly grounded. So, depending on where the neutral is in the system, the neutral could carry fault current. If so, then make sure what ever size you pick will handle the available fault current without damage. If necessary, lay out the cable damage curve over the cb trip curve. Make sure the trip curve is inside of the damage curve.
Depending on where the neutral is in the system, the only protection could be the xfm primary OCP.
cf
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- Location
- Illinois
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- retired electrician
The neutral must be sized the larger of what is required by 220.61 or 250.24(C)(1).
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