I would prefer to bond the XO terminal in the transformer (120/208)housing. Doing so, I would need to float the neutral in the panelboard, but I know that semi-qualified staff will use this panel and they always seem to assume that neutral and ground busses are the equivalent.
Is there a disadvantage to bond the neutral in the panel instead? The secondary raceway is about 3' of 2" greenfield.
John, It would seem to me, if somehow, these semi- qualified individuals were to somehow add a second panel. Either add double lugs at the transformer or a feed through from your setup, they would be relying completely on that bond in the original panel to create the neutral. It is in my opinion the most practical, and safest method to bond your XO at the transformer. Suppose you do you bond at the first panel, and one of these qualified people remove the bonding jumper, because it should be bonded at the transformer. you may be opening up a can of worms.
Thanks Nuts! I know the facility and their people. They would not add a subpanel, but they will add branch circuits. And they will indiscriminately tie ground and neutral to either buss. I see it everywhere.
I know that the bonding can be done at either location as far as NEC goes, but other than my concern about the staff, I'm wondering what others prefer, and why.
It's generally best to ground the neutral as close to the source as possible, as this provides the most efficient path to ground. This will also keep voltage drop between the grounding point and X0 terminal as low as possible, which will keep the 3 phases better centered around ground. In practice, it's only going to make a few volts worth of difference, especially if you're only talking about 6', but it's still more efficient to bond at the transformer.
The particulat inspector on this job implied that it should be bonded at both places, which I believe to be a misunderstanding of the NEC.
I was thinking about bonding in the panel because he would be more likely to look there, as opposed in the transformer housing. (I know this approach may seem questionable, but I was just putting out feelers)