Neutral Connection Requirements of Dual Utility Feeds

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UTA-EE

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I have a situation where there are two utility transformers with solidly grounded wye configured secondaries. We therefore have a 3 phase, 4 conductor service into the plant from each transformer. The service from each transformer is terminated in a transfer switch.

The question is this... Does this transfer switch need to be a 4-pole transfer switch with a switched neutral or is a 3-pole transfer switch with the neutral conductors from each service bonded together allowed? It seems like NEC section 250 covers this issue, but is open to interpretation.
 
This is design issue, unless you have GFP with a 1200 amp service, then you must transfer the neutral or you will desense the ground fault relay.
Good info on this in the IEEE Powering and Grounding Book
You are better off not transferring the neutral, it just causes a whole lot of issues.
But the grounding electrodes for each service must be tied together. See 250.58. If a new building this is easy with a CEE or ufer.
 
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