[RE-wrenches] Neutral to ground bond in a wye wound secondary

[Richard L Ratico]

William,

The transformer creates a Separately Derived System. You need to bond the the
neutral, and the equipment ground there or at the first Disconnecting Means,
which would be the combiner panel. The chosen bonding point must also be
connected to a grounding electrode. Per2011 NEC 250.30.

Dick Ratico


--- You wrote:
Friends:

We came across an interesting situation in a local winery recently:

The service is 480 volts and the inverters are operating at 208 volts.  To 
make the two systems connect, the original installer integrated a 480 Delta 
to 208 Wye transformer, pretty standard procedure.

We found a stray voltage of 18 volts between the neutral and ground as 
measured in the AC combiner panel.  I noticed that there was no bond 
between the neutral and the ground in this panel.  I do not believe this is 
correct.  One reason is the stray voltage seems wrong.  Another, more 
important consideration is that I do not believe there is path for fault 
currents to return to the transformer.  In the case of a phase short to 
chassis, there would be no fault current to open the OCPD.

Is my analysis correct here?

Thanks in advance,

William Miller
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