what is the code article that specifically states where and when bonding bushing is required for transformers?
I am installing a transformer with concentric knockouts that
I won't knock all out, usually I knock out my own eccentric and don't need one.

I beleive it is only required on the load side?

What if I bond XO at panel where I punch my own, would I still need one in x-former?

Thanks,
H20

I think the general rule you use bonding bushings on raceways containing unfused conductors like services. I suppose if you have a transformer secondary conductor before it gets to the first O/C device it should have bonding bushings but I am not sure that is code.

I think Soares is the source of this.

I think in terms of the bonding bushings being used on the 'service' side of any separately derived source, over that portion where the 'ground' is lacking and before the neutral bond.

Don't forget 250.97 2014 N.E.C. . Bonding over 250 volts to ground .