Clarify 240.5, current protection on secondary

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fastline

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midwest usa
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Regarding an OCPD on an Xfmr secondary. Code mentions a 3 wire and a delta/delta as not needing secondary protection, but 4 wire does? Does this mean if a 4 wire capable Xfmr is not tapped for a neutral, it is a 3 wire? I am trying to wrap my head around the potential safety issue that would make the Neutral issue into code? How would that get overloaded?

I've seen a LOT of 208/120sec Xfmrs within secondary protection other than going right to a load center.
 
If the neutral point is grounded it is 4W even if the load does not use it.

I believe the NEC requires the neutral point to be grounded if it can keep L-G voltage below 150V.
 
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